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out, leaving it ready to be drawn up ugain empty by the wagons descending into the »haft. The winding drum over which the rope passe» 1ms generally to be started, and this is doue by a pair of 8-in. cylinder air-engines supplied from the turbine.

The number of hands employed in working the diamond-boring machine is four men—one to each drill—and a boy to look after the engine.—Engineering,

NOTES ON RECENT DISCOVERIES AND THEIR PRACTICAL APPLICATION.*

The Structure Op A Gas Flame.—The flame of a batswing or fishtail burner is seen to consist of two distinct parts—one, nearest the nipple, of s light blue colour, sometimes nearly invisible, and a fringe of luminous flame above. The relative proportions of these two parts depend partly on the quality of tin- gas, but more on the construction of the burner. Small holes or A narrow slit will give more of the blue and less of the luminous part of the flame, all allowance being made for rate of burning and pressure. The constitution of the blue part has been made the subject of study by M. Baudrimout. He finds in effect that it resembles somewhat the flame of a candle. He has not proved it to lie hollow, but he shows that the outer part is intensely hot, and the inner part of a very much lower temperature. A small platinum wire carefully brought to the outer part became white hot, and .even began to melt. The same wire placed across the blue part of the flame remained dark in the middle, and was only made white hot at the outer margins. M. Baudrimont endeavoured to estimate the exact temperature of this outer margin, but seems to have failed in the attempt.

A New Method Of Purifying Water.—Runge lins made some observations on the purification of water, which offer some interesting points. Briefly put. his assertion is that metallic iron offers the readiest and simplest means of disinfecting water, aud of preserving it fresh. With his explanation we shall not now trouble ourselves, but we may say he accounts for the fact that Thames water taken to sea in iron tanks soon becomes perfectly sweet, and remains so through a long voyage. One observation he has made may be of interest to many readers at this time of the year. It is that a small piece of sheet iron or some nails placed in the water in which cut flowers are put will keep the water sweet, and we may suppose the flowers fresh, for a long time. Runge also put some iron filings in a vessel with a very small quantity of water and placed a leech therein, and found the water quite fresh and the leech healthy after six months had passed. We may return to this subject, which bas much interest in a sanitary point of view.

Bleaching Wool.—A French patent, by M. Fregón, describes a novel process for bleaching wool and silk, for which until now we have had oidy the sulphurous acid method. A bath is made by dissolving 41b. of oxalic acid and 41b. of common salt in '200 quarts of water, and the goods to be bleached are left in this bath for an hour, after which they are drained and rinsed in soft water. Oxalic acid we knew to be a good bleaching agent for some animal matters, sponges, for instance, and it may perhaps answer for wool and silk.

To Whiten Yellow Flannel.—Dr. Artus tells us that flauuel which has become yellow with use may be whitened by putting it for some tune in a solution of hard soap, to which strong ammonia has been added. The proportions be gives are ljlb. of hard curd soap, 501b. of soft water, and twothirds of a pound of strong ammonia. The same object may be attained in a shorter time by placing the garments for a quarter of an hour in a weak solution of bisulphite of soda to which a little hydrochloric acid has been added. This latter process we dare say will be effectual, and probably the oxalic acid solution mentioned above would answer the purpose as well.

Bleaching Ivory.—We published last year a process for bleaching ivory which had turned yellow. That method did not appear to us very promising any more than the following, which we give for what they aie worth. The first directs the article to be placed for an hour in a saturated solution of alum, after which it is to be rubbed first with a woollen and then with a limn cloth until it is perfectly dry. The second process, which the writer we qviote from says he prefers, consists simply in digesting the ivory article in thin milk of lime kept hot until such article has assumed the desired whiteness. Then it is to be taken out, dried, and polished. How long it may possibly l>e necessary to continue the immersion the author does not inform us.

Chinese Gold Lacqier.—The gold-lacquer lining of a Chinese cabinet in the Museum at Cassel pealed off, and thus gave Dr. Wiederhold the opportunity of studying the composition of this substance. On examining it he found particles of tinfoil attached to the lacquer, so he comes to the conclusion that this material formed the ground upon which the lacquer varnish was laid. His attempts to iini

* From the Mechanic^ Magazine.

täte the varnish were perfectly successful, and he gives the following directionsfor the preparation of a composition which closely resembles the true Chinese article. First of all, two parts of copal and one of shellac are to be melted together to form a perfectly fluid mixture, then two parts of good boiled oil, made hot, are to be added; the vessel is then to be removed from the fire, and ten parts of oil of turpentine are to be gradually added. To give colour, the addition is made of solution in turpentine of gum gutta for yellow, and dragon's blood for red. These are to be mixed in sufficient quantity to give the shades desired.

Dyeing Horn.—According to С Burnitz, of Stuttgart, horu may be dyed black by a cold process in the following way :—The horn is first to be soaked in a solution of caustic potash or soda, until the surface is a little dissolved, and feels greasy. Then the article is to be washed and treated with Lucas's aniline black, after which it is to be slowly dried and again washed. By exercising a little care, we read that combs with fine teeth may be dyed in this way. The articles look of a dark brown colour by transmitted light, but seen by reflected light they are deep black.

Preserved Bread.—Preserved bread has been suggested by M. Maurice as a substitute for biscuits for the use of sailors, soldiers, and travellers. The bread is made in the ordinary way, and is then thoroughly dried. It is afterwards exposed to high pressure steam for a short time, and is subsequently submitted to hydraulic pressure to reduce the bulk. The cakes so produced will keep, it is said, for years if protected from moisture. Ihey are necessarily hard, but are masticated as easily as biscuits. The process by which these cakes are made is long and troublesome, and the only advantage that they can possess over biscuits consists in the circumstance that they have undergone the primary fermentation which some writers on dietetics allege is absolutely necessary to produce bread of a perfectly wholesome character.

Novel Sea-ooing Vessel.—The model of a seagoing vessel of very original build is now to be seen in the port of Algiers. A general idea of the construction is obtained if we imagine a steamer cut in two, and the severed parts made the support of a bridge four times the length of the original vessel. This bridge has an air-chamber in its entire length, so that if by accident it should become parted from the supports it cannot l>e submerged. It is destined for the cargo, but cabins in the form of boats are so arranged along the sides of the bridge that in case of accident to this latter they may be navigated separately. Thus there are three chances of safety if the construction goes to pieces. The supposed advantages are—first, great speed (since the larger part of the vessel not being in contact with the water the resistance is so much diminished), safety, and great space for cargo. Something of this kind has been projected for taking railway trains aeróse the Channel, but we do not remember to have seen it suggested for vessels going a long distance.

Iron And Hydrogen.—A curious observation has been made by M. Caron on an alteration produced in iron when it is kept melted for some time in an atmosphere of hydrogen. The metal, we read, somewhat increases in density and becomes soft and malleable as copper. Re-melted in a crucible it becomes scaly when cold, doubtless in consequence of the evolution of absorbed hydrogen. Are we to regard the softness and malleability as the properties of an alloy of hydrogen and iron?

Wings Of Birds.—By means of an ingenious little apparatus M. Marcy has proved that in flight the tip of the wing of a bird describes a simple helix. An instrument placed on the back of я bird follows the figure and registers it on a card. The wings of insects, the same authority shows, have only an np and down movement, the extremity of the wings describing only a wavy line.

Ortainino High Temperatures.—A very useful invention of Mr. Coffey is now to be seen in operation at Messrs. Donlton it Watts'», of Lambeth. It is a new mode of obtaining high temperatures for the evaporation of liquids without the use of high pressure or superheated steam, and is, in fact, a modification of the circulating system, heated w;ater being replaced by heavy paraffin oils. These circulate exactly like water. A close system being made, the oil heated in a coil of pipe placed in a furnace rises first to an air-tight tank, from which it runs through pipes and the jackets of pans, descending as it cools to the coil of pipe in the furnace. With this apparatus a temperature of 600° or 700° Fahr, may be safely maintained without any of the risks arising from the use of »team at high pressures, and, as will be easily seen, with a much less expenditure of fuel. A pyrometer is contrived to show the exact temperature of the oil as it leaves the tank, and means are provided for regulating and keeping the temperature uniform. We look on this invention as destined to achieve great resalte in many industries.

The fourth consecutive crop of wheat is now growing on sewage-mauured land at Barking. The stalks are ahnut 5ft. high, with ears of great length.

SCLENTLTia SOCIETIES.

BRIGHTON AND SUSSEX NATURAL HISTORY SOCIETY.

A MEETING of the Microscopical Section was held on the 23rd ult., Mr. Glaisyer, Vicepresident, in the chair. The subject for'the evening was " Infusoria," which Mr. Wonfor introduce«! by a few remarks. As all were aware, he said, if any vegetable or animal substance was placet! in water, in a few days the water would be found fuU of minute organisms, to which the name "infusoria," or infusion animalcules, had been given. Many forms, though figured and described as distinct species, had since been proved to be only the early stages of other animals, others had been classed among another group of animals, while a very large number were arranged among plants. ТЬн class infusoria was much more limited than at one time supposed, and increased knowledge and further research might prove that many more were only the early stages of other and higher types of life. Mr. Wonfor then proceeded to point out the nature of their substance, their mode of development, increase, and propagation. So widely were they distributed that scarcely anywhere could water be found which did not contain some infusoria. Many would live only in fresh water, others in salt or brackish water, while others were to be found only in water containing decomposing vegetable or animal substances. Hence water contaminated by sewage matter always showed certain types, while some occurred only in particular infusions others were common to several. Their appearance under certain conditions had led to theories on spontaneous generation, a much debated and debatable point; but as the atmosphere, according to Tyndall and others, appeared to be full of germs, their suddcu appearance under favourable circumstances was not surprising. The water in which cut flowers were kept was sure to yield some sorts ; in fact he had obtained an abundant supply of one kind from water in which mignonette had been only three days. Water in bird fountains and water bottles if not looked after and frequently changed, would be sure to contain infusoria.

ETHNOLOGICAL SOCIETY.

A Special meeting of this society was held at the Royal United Service Institution on the 21st ult.. Professor Huxley, LL.D., F.R.S., President, in the chair. Colonel Lane Fox mode some remarks on the Dorchester Dykes and Sinodun Hill, to which attention has recently been directed, and showed that the works are British and not Roman. He stated that the demolition of these works has been arrested for the present. Mr. David Forbes, F.R.S., read a paper "On the Aymara Indians of Bolivia and Peru." He described them as a small, massive, thick-set race, with large heads and short limbs. The trunk is enormously large, and the thorax extremely capacious, being adapted to meet the requirements of respiration in a rarefied atmosphere, as the Aymara lives at an altitude of from 8,000 to 16,000 ft. above the sea-level. The proportions of the lower limbs are curious, the thigh being shorter than the leg: the heel is inconspicnous. In colour the Aymara varies from copper-red to yellowishbrown and blackish-brown, according to the elevation at which he lives. Many of the customs of the Aymarás depend on their conditions of life. In consequence of the low boiling point of water at such great altitudes, beans are rarely used, and the food consists chiefly of potatoes peculiarly prepared. Clay is added to the food, not for any nutritious matter in it, but merely to increase the bulk of the meal. In religion the Aymarás are nominally Christians. They appear to have no system of writing.

The discussion on this communication was supported by the President, Mr. E. G. Squier, Mr. Cull, Mr. Dendy, Mr. Bollaert, Mr. Harrison, and Mr. C. Markbam.

At the same meeting Dr. A. Campbell exhibited tracings of certain rock-inscriptions from British Guiana, and the Hon. E. G. Squier displayed я large collection of drawings, photographs, &c, from Peru.

LONDONDERRY NATURAL HISTORY AND PHILOSOPHICAL SOCIETY.

At The concluding meeting for the season of this flourishing society Dr. Cuthbert read a paper on the Abnormal Arrangement of Organs in the Human Subject. A young soldier of the 28th regiment met with a fatal injury in the month of February, 1868, at Knocknlla Fort, near Rathmullan. On a post mortem examination of the body it was found tirât the liver was ruptured, which was the cause of death; that the liver occupied the left, and the stomach and spleen the right side—the parts being thus transposed, the intestinal canal was also abnormally arranged. In the chest a similar malposition of parts was found—the heart occupying the right side, and the great vessels proceeding from it as usual, but transposed. The man seemed to have been of a delicate constitution, and, as appeared from his history, was unable to bear mach fatigue. It does not appear, however, that he suffered from any ailment to which the unnsnal arrangement of his internal organs in any way contributed. The transposition of the viscera is certainly к sufficiently rare occurrence to warrant a notice of the point. We can only regard such abnormal arrangements as are occasionally met with as strange freaks of nature, with no appreciable influence on the health or habits of their subjects. It seems a strange circumstance that, in no instance that can be discovered, has an abnormal arrangement of the viscera, as the result of natural traneSosition, been ascertained, or even suspected during fe—a fact which would argue one of two conclusions, either the extreme rarity of the cases, or the exceptionally good health of those who are the subjects of such transpositions.

THE ROYAL IHISH ACADEMY. At the last meeting of the Boyal Irish Academy, June 13, Dr. Sigerson, F.L.S., read a paper entitled "Further Researches on the Atmosphere."

In order to obtain an accurate knowledge of what is usually and what is occasionally present, it appeared requisite to make a careful examination of particular atmospheres as well us of the general air. After detailing his mode of operation, he proceeded to describe the objects found in the sediment from the air taken from ledges above man's height, and observed likewise in the atmosphere.

Iron-factory air, a friable black dust ; on examination, this was found to be made up of particles of carbon, of ash, and of iron. The carbon formed the largest masses, the ash-particles were reddish, or white and opaque. Some transparent pieces with а glassy fracture were noticed, and were regarded as glass resulting from the fusion of sand used in the welding procès?.

The results of the study of the several other atmospheres, and their effects upon the health of those abiding in them, were described at length. A brief summary is all that con be given here. In "shirt-factory air," fine filaments and fragments of cotton and linen were found, with a few minute ova, not generally dispersed. The girls employed in the factory had become snuff-takers. In the atmosphere of " threshing-mills," fibres and fragments of chaff, awns, grain, together with some smut-balls, were found. In that of oat-meal mills, libres were seen in unexpected number, together with minute fragments of the pericarp of the caryopsis and starch-granules, with a rare spore and an acarus. This air was not so injurious as that of " flour-mills," the dust being less. The atmosphere of mills where flax is " scutched" was found to be so bad, that these mills could only be regarded as human slaughter-houses. In the air of printing-offices, from various symptoms observed, antimony was believed to be present. In consequence, some dust taken from a rafter eleven feet above the floor was submitted to the secretary of the Academy, Professor W. K. Sullivan, whose analysis confirmed the accuracy of the expectation. Antimony was found and no lead. In the " atmosphere of stables " were found moth-scales, some larva, eggs, spores, and a great quantity of cuticle-scales and fragments of fine hairs, with some corpuscles and fragments tinged blood-red. An acarus was present in the dust. Hairdressers had a similar atmosphere, so far as distinctive elements, scales and hairs, were concerned. The "machine-brush" increased thenamount.

Tobacco-smoke, with some difficulty, was got under the microscope. It was examined on entering and on leaving the mouth. Little globules of nicotine were discovered twirling and flitting about in it, like monads. Some remained on the walls of the month; when the smoke was breathed (by novices), more globules were retained in the lungs, and nausea and illness supervened. These globules, if found in the air, distributed by a cigar-smoker, might be mistaken for germs, as they would resist the iodine-test for amyloids.

In order to arrive at the cause of the ill-health of "tea-tasters," their special atmosphere was examined. In pursuing their avocation (selecting teas), they had to take a sip with quick inhalation, and thus a small shower of fine tea-drops entered their lungs. On examination of such tea-drops, a considerable quantity of libro.vascular and cellular tissue, from the leaves, was found which might aid to tease the lungs. "But the real agents of mischief were numerous droplets of essential oil, very plentiful in Assam tea, which was particularly severe on the tea-tasters. Nausea, disarrangement of the nerves, and sometimes syncope afflicted them.

As a result of numeroue observations, some of which ore here recorded, Dr. Sigerson considered himself justified in drawing the following conclusions :—

1st. That stomach signe—irritability, nausea, dyspepsia,—are frequently symptomatic of interference with the lungs; so that the stomach, in such cases, may obscure the symptoms, but will not cure the disease.

2nd. That the lungs have a power, not hitherto suspected, of absorbing or assimilating even solid matter.

3rd. That the theory of the panspermists seems unfounded on fact—that there are no hosts of germs always floating about in the atmosphere, invisible and maleficent as genii of Eastern stories. Air is not much better, but not generally worse than water.

5th. The "germ theory" asserts " that epidemic diseases are due to germs which float in the atmosphere, enter the body, and produce disturbance by the development within the body of parasitic life." It is opposed to the opinion that epidemic diseases are propagated by a kind of malaria, which consists of organic matter in a state of motor-decay. It is supposed to be supported by certain statements about the non-occurrence of putrefactive changes in closed vessels, which have been disputed and by the statement that retten malaria cannot act like leaven, because fermentation is caused by the growth of the yeast-plant. Now, the effect of the growth of parasitic plants in causing skin-diseases is well known; il they caused epidemics likewise, thenpresence would, in all probability, have been as soon detected.

THE NORTH STAFFORDSHIRE NATURALISTS' FIELD CLUB.

That portion of the Valley of the Manyfold which is nearest to the village of Wetton, was chosen for the third meeting for the season.

The party struck the valley, not far from the once celebrated Ecton mine. At a cavernous opening near Wetton Mill, Mr. Carrington, the veteran geologist and barrow-digger, was superintending an excavation in its floor. No proof was obtained in the shape of fragments of charcoal and such objects that the hollow had ever been inhabited by primeval man, but only clay and water-worn boulders of millstone grit, no doubt carried in when the surface of the country was very different, and the rivers larger and at a different level to what they are now. Pebbles from the same formation (the millstone grit) were pointed out by Mr. Carrington adherent to the sides of the limestone cavern. Later in the day bones were dug out of the clay, especially one large vertebra. In the cavern Mr. Carrington read a short paper on the duties of a field naturalist. He ended by exhibiting his original pen-and-ink sketches of the articles exhumed by himself in the floor of Thor's cavern, towards which the party now directed their steps. The instruments discovered were of the RomanoBritish period, in stone, bone, bronze, and iron. The cave was not a true bone cave, like those of Gibraltar or Kent's Hole for instance, with bones below a layer of stalagmites or imbedded in it, nor did it yield traces of primeval man, such as weapons of flint, but it appears to be a water-worn hollow filled below with clay and stones rounded or smoothed by water-transport or attrition, and more recently the haunt of our British forefathers.

LETTERS TO THE EDITOR.

[We do not bold ourselves responsible for the opinions of onr correspondents. The Editor respectfully requests that all communications should be drawn up as briefly as possible.]

*** All communications should be addressed to the Editor of the English Mechanic, ;il, Tavistockstreet, Covent Garden, W.O.

All Cheques and Post Office Orders to be made payable to J. Passxore Edwards.

"I wonld have every one write what he knows, and as much as he knows, but no more; and that not in this only, but in all other subjects: For such a person may have some particular knowledge and experience of the nature of euch я person or such a fountain, that as to other things, knows no more than what everybody does, and yet to keep a clutter with this little pittance of bis, will undertake to write the whole body of phy sicks: a vice from whence great inconveniences derive their original,"—Montaigne's Еыаув.

ASTRONOMICAL.

Sir,—There is a small comet (D'Arrest's) in Serpens now; but "W. R. " (4Ш> p. Й35, will scarcely see it with the naked eye.

The extract given by "Foreigner " (41ö0), p. 368, from a Brussels paper, ík just a little obscure. How in the world a comet " on the East of the Bun " can be seen "after midnight " passes my very limited comprehension. I have heard nothing of this comet of Winnecke's, inasmuch as the circulation of an Ephemeris of a newly discovered one among the English observatories, is quite beneath the dignity of the editor of the Royal Astronomical Society's publications. We are only too thankful, as a body, to get our " Monthly Notices " a month after the meeting at which the papers they contain were read. It is only some radical and revolutionary spirits who have dared to hint that we are entitled to early intelligence of recent discoveries in the heavens; but these obtrusive people, however, are crushed out by the sublime indifference of the editor referred to.

'• W. H. С." p. 358, puts two questions (4131 and

4133). With regard to the former, I may perhaps be forgiven for saying that, as it stands, it has to me no meaning whatever. With respect to the latter, if your correspondent will torn t •■ \>. 649 of Vol. 10, and to pp. 1 and 2 of Vol. 11, he will I hope there find the explanation which he seeks.

Mr. G. Firth is good enough to criticise my very unpretending "Astronomical Notes" for June. It i* quite right as to the pleonasm involved in the employment of the word "a.m. on the next morning,"'I have no means of knowing whether it was a lap$i§ calami on my part, or a printer's blunder. Certainly I am not responsible for the 7h. 12m. to which your correspondent refers, save to the extent, perhaps, of making my l's and 7's something alike. The word 11 afternoon" though, in the context, would suffice to show most people that 7 o'clock could not have been intended, as that is an hour usually and conventionally ascribed to the evening. With regard to Mr. Firth's remarkable peroration, it may su Шее to say, that as the so-called signs of the zodiac are only twelve divisions of the ecliptic, quite irrespective of any stars whatever, it certainly seems to me—in my weak-minded way—that the position of a planet can be better given by referring it to a known and (practically) unalterable constellation, then to an abstract and impalpable line. Doubtless the precession of the equinoxes is (from the Firth point of view) very annoying; but still, as an obvious result of the law of gravitation, I do not quite see how it is to be got rid of; and as its sole object, pro hoe vice, is to shift the origin of certain imaginary co-ordinates, I am unable to see what good I, or any other astronomer could do by asserting that a planet was in such and such a " sign," which no one could see, instead of saying that it was in a given constellation, known and visible to everybody. Does Mr. Firth imagine that the readers of the English Mechanic would find on object more readily from so eccentric a description? A Fellow Of The Royal Astronomical Society.

m

"BARTON'S PATENT SELF-ACTING FEED WATER HEATER FOR STEAM BOILERS."

Sut,—On page 302 of the English Mechanic. Jane 17th, I observe a portion of Mr. Basker ville'* letter devoted to criticisms on Llah's or Hall's économiser, implying doubt as to the general efficiency and economical results of feed-water heaters. He says, "The temperature of Che waste steam escaping from a non-condensing engine is 212 degrees or so, and that is the maximum of heat it can impart to the feed-water passing through it, but as a matter of fact it never does so by many degrees." So much depends upon surrounding circumstances in connection with this question, it wonld be premature to fix any given standard of heat to the steam at the outlet of the exhaust. Expansion of steam after out off, reducing its elasticity, and consequently loss of heat, with distance from cylinder to exhaust outlet, may be said to form primary canse of variation in changing the temperature of exhaust steam imparted to the feed water. Deductions and calculations made by figures, from & scientific point of view, are all very well in theory; unfortunately they do not always harmonise in practice. Again he says, "There is no appendage of the steam engine which is less understood than the feedwater heater." This we quite agree wit.li. If it weit» better understood, it would be more hugely adopted, to the great satisfaction of steam tubers доиегаЦу. I can assure Mr. Baskerville (whatever his ligures may say to the contrary) that the " inevitable" 23 per cent, saved in fuel is not " a delueion," but a practical fact with feed-water heated to 212 degrees. I have, by careful and trustworthy experiments, proved the truth of those statements, by weighing the coal used week for week, doing the same amount of work with the engines in both experiments ; that is to say, one week with cold water, the other week with water heated to 212 degrees by the économiser ; in all oases the statements have been fully confirmed. Having had charge of one of these heaters for over twelve months (" Barton's," as represented by the above illustration).

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I will, Sir, by your peraiission, endeavour to enlighten your correspondent on what he calls the overrated results of these contrivances. The fallacy of using theoretical argument in opposition to practical results requires no further comment.

The means by which the feed-water is heated by Mr. Barton's plan, is by using the waste or exhaust steam;

Elacing on some portion of the exhaust-pipe a cistern. ato this cistern, the exhaust steam is admitted at the end, and the exit from the other. The admission of cold water into the cistern is regulated by a float placed in the inside, and this float is always being moved by the force of the exhaust steam blowing upon it, thereby securing the constant supply of feed water. The engine blowing the exhaust on the water in the heater under my charge in 14 horse-power nominal, pressure on the boiler4ШЫ. to tho square inch, making 60 revolutions per minute, length of stroke "2ft. tun., cutting off at half stroke, passing through the heater about 6,009 gallons of water per day, with a continuons temperature of 212 degrees.

The efficiency, simplicity, and durability of this heater will be best understood by consulting the following description. (See diagram.)

A. Tank for the heated water.

B. Pipe for conveying exhaust steam into the water.

C. Tap for cold water supply.

D. Float.

E. Test-rod.

F. Hot water supply for the feed-pump.

(т. Pipe for conveying away the surplus eteam.

H. Guage showing the height of water.

I. Thermometer showing the temperature of water.

J. Man-hole.

K. Lever for opening tap С

1». Cold water supply-pipe.

G. Tap which is coupled to a lever К and flout D. where the water in the heater raises the float D, and closes the tap G, and so reduces or shuts off the supply; and when the water-line is lowered by increased withdrawal through F, the float D failing, and opens the tap C, augmente the supply of cold water flowing through C. The nozzle of the tap G is arranged to deliver into the beU-mouthed steam-pipe It, directly on the cold water heating to boiling point. E, test rod, whereby it can be ascertained, without »moving the man-hole J, whether the tap С i-* working freely. It is impossible for the tap G to get out of order, for every stroke the engine makes it moves the plug G.

When we consider the extent to which ae a nation we are dependent for our commercial prosperity on steam power, and that this power is increasing every day, prejudice, or lack of information ought not to stand in the way of any modern invention, having for its object (as thin invention has) the improvement, if not the perfecting of a system the want of which has long been felt. The many existing proofs Rent to the patentee, Air. Barton, in the form of testimonials, as well ae verbal declaration« personally made of the great utility ae an économiser of fuel und water, would in thamselvee be a sufficient justification for its introduction to the public. There are other results, as follows, though of leas importance individually, yet no less momentous as a whole.

1st. Its safety to the boiler, by preventing the sudden and unequal expansion which takes place when cold or partially heated water is introduced.

2nd. By relieving the engino of back pressure produced by heaters of other construction. By purifying the water, and precipitating deposit before it enters the boiler. By using the exhaust steam for heating the feedwater, and giving to the boiler a regular supply at boiling point, thereby saving 25 per cent, in fuel. It supplies a practical safeguard against explosion, by making it impossible while the engine is running to introduce cold water into the heated boiler. It increases the staanxmg and working capacity of the boiler, the generation of gteam with a given amount of fuel being much greater than when the boiler is supplied with water cold or partially heated. It saves water by the condensation of steam, which takee place in the heater, again returning to the boiler. It is perfectly selfacting, thereby doing away with constant personal attention. It frees the boiler of old scale, and other incrustations, and prevents the same from re-forming. It has other advantages, and is easily adapted to engines of any construction. I know that it is becoming extensively patronised by engineers, iron forges, boat-builders, steam sawyers, and steam user* generally. I see by a testimonial from Messrs. Laird Brothers, Birkenhead Iron Works, that they adopted one of these beuters еошо months ago, and found the saving so considerable, and the working so satisfactory, they have now applied it to all the principal engines in the establishment.

Engineers, boiler-makers, and steam users of every class, would do well by making themselves thoroughly acquainted with the many advantages to be derived from the use of this heater.

Though simple in its construction, it accomplishes in the most perfect and satisfactory manner an astonishingly large number of very important results. Space would not be allowed me, or I would have forwarded to you for the information of Mr. James Busk er ville und others, a tabulated statement of the saving in coal and water, extending over a period of three months, with three single fire fined Cornish boilers, supplying steam for engines of 50 horse-power with u number of steam hammers. Should Mr. Boskerville or any other of your correspondents require any further information in reference to this heater, Ï should feel great pleasure in replying to anv such request.

S. Crompton, Birkenhead.

[3]

THE TELESCOPE, Etc.

Sib,—There is a qucrr, headed "Object Glass" (4088), on p. 885, which at the first blush is unintelligible. On reading it over, however, two or three times, I have a dim notion that it has to do, not with tin object glass, but with the terrestrial eyepiece of a telescope, and (assuming that I understand the nature of the question), I may inform "О. B." that his lenses 1 and 3 should be ljin. apart. At ¿in. from No. 1 a stop must be placed to define the field of view. His lenses Я and 4 may be placed 4jin. apart. The distance between Nos. 2 and S may bo Varied within considerable limits. The farther they are separated the higher will be the power. 7in. would be a good working die*

tance, with the considerable focal length of the component lenses in your correspondent's possession. I may add that I do not believe that the dimness of whioh he complains has anything to do with the interval separating the two combinations in his eyepiece, which, as I have said, admita of considerable variation. If his object glass be not faulty, I ehould unhesitatingly attribute the defect of which he complains to the disarrangement or imperfection of the little stop between his third and fourth lenses. The adjustment of this must be made with scrupulous care, and the opening be otjust sufficient size to let the creasing ravs pass through it. If it be too small it will diminish the effective aperture of the object glass. If it be too large it will let a quantity of false light through, which will fog and obscure the image. I question the ability of any one possessing the somewhat limited knowledge of your querist to make this adjustment for himself, and should advise him, by all means, to send his eyepiece to some working optician.

I may answer "Urämie" (4109), same page, by telling him that Chance's price for their warranted optical crown and flint glass of the size that he requires is £7 4s. per disc, so that a pair of 6in. in diameter would cost him £14 Be. His trap tools may be a little larger in diameter than his lens; his polisher should be rather smaller. He may go on grinding his lens with very finely washed emery until the image of a candle can be seen in it. He can then transfer it to the polisher. I have strong reason to believe that alpaca is the best material for that polish. I really cannot tell how many hours a lens occupies in taking a polish, as I have never worked at one except in a desultory way, but I know that polishing is very tedious work. Some of our opticians, who can speak ex cathedra on this eubject, may probably give "Uranus" the information he requires on this sub ject.

Regarding the inqniry of "Urban," on p. 881, as а quasi-optical one, I may tell him that my knowledge of bisulphide of carbon prisms is to a great extent theoretical, my practical experience of them having been confined to the employment of two belonging to a friend.

"W. C." (4183), p. 848, has done pretty fairly in seeing Jupiter within 9° of the Sun with his 84-inch mirror—albeit, he has not achieved anything very surprising. I have more than once seen Venus with a much smaller instrument, when the glare of direct sunlight was just beginning to be perceptible in the field. I do not think that he would see Mars any nearer to the Sun than he could see Jupiter, but Mercury he certainly ought to be able to follow nearer to the Solar limb. He will find a very constricted field a great help in viewing a planet under such circumstances.

"E. G." (41Ü6), also on p. 858, can do nothing with his object glass. It must be re-ground and polished to get rid of the scratches upon it; and this, if it be of any value, would assuredly ruin its figure. The process of grinding and polishing has been described over and over again in your commits, but is certainly beyond the capability of any one who, like your correspondent, knows nothing at all about it. If he should choose to risk spoiling its figure he had better take his glass to a practical optician, who would, at all events, eliminate the scratches for him.

Л Fellow or The Royal Astronomical Socxxtt.

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Stn,—Your readers are too numerous, and like all the public, too little informed upon the subject of the production and consumption of gae, to allow such remarks as those of "C. D. E.," p. 354, to pass unnoticed; and as I happen in the course of my life to have had practical acquaintance with the eubject, I take on myself to inform your readers that " C. I). E." evidently knows nothing whatever about the matter. He says, " good coal gas is rich in these vapours as it passes out of the retorts, but the gas companies find it expédient to extract a greater part of these condensable vapours and supply their customers with a very low power illuminating gas." A more misleading statement was never uttered, even by the gas quacks, who for years have made it their business to go about making false statements in order to get up squabbles between gas companies and their customers, and particularly with the corporate bodies who con pay "expenses."

The companies are bound to supply a gas of a power which was fixed as being the limit obtainable from Newcastle coals; as a matter of fact they are obliged to use a portion of expensive cannel coal in order to insure the gas being up to that standard. The vapours they remove are those which, being condensable, would otherwise form deposits of napthaline, Ac, in the mains and services, and gas manufacturers are doing all they can to secure these vapours being made into condensable gases.

A little anecdote which I can vouch for is a good answer to such a statement. A certain company was summoned for allowing condensed liquids, removed from the mains, to pass into the sewers, and some marvellous statements were made as to the danger of such a course. An eminent witness, who ought to have known better, asserted that the gas companies put naphtha in the mains to raise the illuminating power of the gas clase to the services, and that it was naphtha thus inserted which was the source of the danger. "In that case," said the company's engineer, "Why do we pump it out into the sewers?" It is needless to say the witness looked somewhat foolish.

The fact is that almost every complaint made by gas consumers may be traced to their owu mismanagement, and the want of care and knowledge by gas-fitters. Bad burners are used, and small pipes expected to supply

endless lights, while half the lights arc allowed to burn with ragged flames and the gas hissing away, giving nothing like its proper light, and the fault is of course hud upon the gas company. As to price, I can tell Londoners as a fact, that they now pay (id. and per. haps !M. a thousand more for their gaa than would be the case but for their so-called friends, who, saddling the companies every year with the law expenses of a parliamentary fight, put that cost on the gas, for every effort is made to reduce cost and priée, in order to increase cou sumption. As to carburetting gaa, the beat evidence that it is not a practical process at present, is that numerous as are the patents and processes, none have established themselves in use. Siaxa.

THE CLAVICHORD, ITS CONSTRUCTION, KTC, Sir,—The loudness of the sound« of tarns, and, indeed, all other stringed musical instrumenta» must, emtêrim paribus,he in proportion to the force with which its string s are struck ; and as this will be, c<rt*tri* paribus, in accordance with the velocity communicated to the tangent or string-striker, it would appear that the direction of improvement—so far as the action is concerned—will be to insert the tangent in the key м far from what is termed the key balance (i.e., the surface on which the key rotates), as is consistent with a reasonable width of case. For carrying ont this it is preferable to make the key balance as near as can conveniently be done to» the ivory, say within fin.; and if the strings of the instrument be disposed like those of a horizontal grand piano (which is far preferable to arranging them like those of a square piano) the tangent-may be as much us three or four times as far behind the key balance as the linger acts on the key in front of it.

With an instrument which has but little width from back to front, whose strings are disposed obliquely like those of an old clavichord, virginal, spinet, or the square piano, it is impossible to insert the tangent far behind the key balance in the bass. This, beside* much weakening the force of the blow, has the disadvantage of enabling the player to presa the tangent against its string with far more force than is required to enable it to act efficiently as a bridge. Thi« evil might be cured by inserting the tangent into a lever situated between the key and the string. By this Jj-rangementany required velocity might be communicated to the tangent, and the force of the blow might be farther augmented by loading the intermediate lever» just as the keys of a clavichord with its siringe arranged like those of a harpsichord or horizontal grand piano might be loaded to any extent which did not make the touch too heavy. It is obvious that the greater momentum of the loaded key or lever must cause the tangent to strike the strings with more force than the smaller momentum of a key only loaded sufficiently to cause it to rise can do. The ancient clavichord was capable ol executing very rapid music, as is obvions from its construction ; in this respect it surpasses,either the harpsichord, on which it is possible to play a melody in pretty close repetition, or even the pianoforte. In both these instruments the striker is not rigidly connected with the key, and even in horizontal pianos the hammer« do not always fall as quickly as the key risos in front. Their hoppers descend faster than the hammers can follow them, especially if the hammers be supported on checks ; but nothing of this kind can occur in the clavichord: its hammers 4 tangents) are fixed in the keys, and must descend with them, so that no keyed instrument can bo made to repeat more rapidly than a clavichord, whose keys are pretty heavily weighted; but it has the defect that its sounds cease the instant the key begins to rise, far then the tangent leaves the string and it is effectually damped by its cloth. This, whioh is a defect whan performing melodies*in repeat» becomes an excellence for ordinary playing, for the sounds do not run into each other Uke those of bells, harmonicas, dulcimers, and other instruments which have no dampers—not to mention pianos with more or less efficient dampers, which, by the way, seldom act so perfectly as I could wish. Even when they can act» their proper action is too often prevented by that class of performers who, so long as they can make a great noise, are not at ail particular about discord, and treat their suffering hearers to the chromatic scale with the damper pedal held down throughout their abominable performance.

As formerly constructed, the « lavichordist had bat little power to strike, but he had great power to pres* the strings of hit instrument; consequently the tone must have been feeble and its pitch uncertain, for any increase of the pressure of the finger must have increased the tension of the string ami caused its pitch to rise. By loading the key and placing the tangent far behind the key balance, we should not only greatly diminish the performer's power to produee these disagreeable results, but if the weight of touch was increased to about three ounces—which is not heavier than many modern pianos—the blow would become sufficiently powerful to put a pair of No. 22 or 24 steel wires, 27 inches long, into strong vibrations. Perhaps for the easy performance of very rapid music, it might be well to keep the weight of touch within 2J02., which modern pianists would term a light touch. I hay* known Sjoz. used, but it is unpleasantly heavy until, like the skinned eels, you get accustomed to it It is obvious that in clavichords of the ordinary construction one-half the force of the blow is entirely wasted, so far ae the production of musical sound is concerned, for that part of the string which is damned (although it receives a blow of equal force with that which strikes the vibrating part) is prevented from sounding; hence it is not surprising that the aetato German intellect soon devised a method of utilizing this hitherto wasted force by employing it for the production of sound. This is the principle of Silberman's Double Clavichord, in which the tangents are made to strike its strings exactly :tt their centres, t.«. between its two bridge» on its one or two soundboards. If four strings eon be pat into vibration witbont abstracting anything from the force of the blow, it followb that, cxttris paribvg, the loudeess of the sound will be doubled ; and in a clavichord with such long, thick, and, consequently, very tight strings, as 1 have suggested to be made, the chief objection to SUberman's plan could hardly obtain, for, with its tangents tout- or nve huir- as far from the key balance as the únger tots in front of it, the player will have but little power to prêÉê the strings sufficiently to raise their pitch to any objectionable extent. A very alight rise of the pitch, only just gnfficient to give prominence to the melody, the ear ran endure: it is not only bearable but етея desirable аз one means for expression, which is the eoal of music, and chietly distinguishes the performance of beings possessing minds from that of the barrel, who«« brass fingere not only exceed ours in number but, being actuated by u force purely mechanical and always in their гц/hi ju/oees. don't ever make mistakes during performance—a thing some of ns intellectual beings have been more than suspected of doing.

It is obvious that a double clavichord, à la Silberman, mast be provided with dampers which can be removed from its strings. The single clavichord is most effectually damped by interweaving a strip of list with its strings between one of their resting places and the place at which the tangent strikes them; but as this would permanently damp one-half of the strings of a double clavichord, a removable damper becomes a necessity. The very be -t damper for horizontal strings that I know of is the one iornwrly used in old square pianos, which is so attached to the key that the preponderance of the keys is utilized to press the dampers to the strings. To carry out this principle it is quite unnecessary that tbe connection between the key and the damper be permaueut, any simple contrivance which connects them when in ase will serve; but it is very desirablo that the parte may be easily disconnected when needful, so that any one individual key may be taken out with great facility. There are several ways of doing this, probably the simplest is to gnide the damper wire sticker by an upper and lower socket, and to have two screw buttons on it, one above and the other below a fork made in the further end of the key itself, which should be rednced about {in. thick at its further end, by rebating its under side for about lin. its length. This fork should be wide at its extremity, and its prongs tapered for the first gin. of its length, so that when putting in л key it may allow the damper wire to enter easily. The damper is regulated by turning up the lower nut or screw button until the key is supported at the proper height in front by the damper resting on the string. Should tbe clothing of the dampers become unequally compressed, some of the keys will be lower than others, and must be raised by turning up the lower screw buttons on the damper wires. The upper buttons may bo adjusted to a position sufficiently above the upper surface of the keys to allow 11 ie ш to rise some distance before they commence to lift tbe dampers. The amount of this so-ualled "wast« touch '' is not important so long as the damper be lilted sufficiently to prevent auy part of its surface from tonching the strings when at its widest vibrations. In practice it is best to allow the key to descend from one to two-thirds its total path, so that the key's momentum may prevent the additional weight of the damper being felt by the finger as an increased resistance. Of course these observations apply rather to pianofortes, in which the finger has to raise a hammer detached from the key, than to the clavichord, in which the Ьашвшг is att&ciud to the key; but, even in the latter instrument—the weight of whose damper head and its wire sticker is much lees than the loaded damper of a pianoforte—I think it would be desirable to allow some waste touch between the key and the damper. The design of J. Jenkinson for a double treble piano is at first sight something like a Silberman Double Clavichord : both have the great advantage of enabling as to duplicate tbe unisons without any increase of tensile force ; for it is obvions that a string stopped or toached at its centre, and speaking the octave above the sound due to its whole length, is rendered no tighter than when uttering its fundamental sound. I don't know if Silberman carried out this principle throughout the entire compass; but, if he did, his doable clavichords mast have been as long or longer than a modern concert grand piano. Probably the additional power of sound obtained by this system was not required in the bass, and. as in Mr. Jenkinson's piano, it was only carried out in the two or three upper octaves. Silberman's plan had one great advantage over Jenkinson's, not from any fault which can be eliminated from the design of the latter, but which is inherent in the clavichord over the piano. In the Utter the hammer does not also serve for a bridge; so, to carry out Mr. Jenkinson's idea, I had to provide two very fina bridges and a bicephalus, or rather two hammers. In the clavichord these metal bridges and one of the hammers are not required, simply because the one metal hammer (i.e. the tangent) serves at once to strike both that part of the long string which is to the right of it [or above it in an upright clavichord), and the other portion of the string which is to the left or below it. This, besides its far greater simplicity, entails the avoidance of one of the greatest defects in Mr. Jenkinson's plan, viz., the necessity of tuning each portion of the long string separately. In the clavichord this Is not required, because it can" be tuned by applying the straining force at one end only; for it is'obvious that, when its vibrations are accelerated by increasing itsi tension, so that its pitch is raised (say from В to nrWdie О when vibrating as a whole) the pitch mast be raised from В to pitch С also when struck and stopped at its middle and compelled to vibrate in two unisonous parts, situated one beyond the other instead |

of alongside ад usual. The one thing needful for correct intonation is to adjust the tangeut so that it shall striko tbe long string exactly at its centre between the two bridges on which the string roots, which are attached to the one soundboard or two soundboards. It will be seen that in the clavichord there is not, as there is Ы Mr. Jenkinson's plan, any risk of altering the tension of one portion of tbe long string which han already been correctly tuned, by increasing or diminishing the tension of the othor portion of the same string for the purpose of raising or lowering its pitch to bring it into unison with the portion previously tuned.

Nearly a year ago, when requested to advise "Ye Workynge Man"—then very hot, indeed, on building himself either an organ or a piano—how to construct the latter, I was tempted to repeat Punch's advice to persons about to marry, "Don't." I recommended that most important member of "ye bodie politique" to make himself old Jiach's favourite instrument (the clavichord) instead. I doubt not some of my practical friends, '*W. T." especially, smiled at my ignorance; but wo complicated an instrument as a piano, requiring great a variety of special tools used by different workmen (for in pianoforte making labour is greatly divided) for its production, did not then seem to me a very promising subject for amateur art. It appeared even yet more hopeless than the then popular working man's organ— I mean musical organ. N.B. The E.M. is not only his but otir organ also in another sense, and a very good and improving organ it is. It " goes ahead" as if it knew no stops whatever, except those it puts on the progress of its rivals by buying them up, и process which must iu time make it a very " full" organ indeed, and I hope will cause its contributors to express their " scientific opinions" and to "pipe" harmoniously. To return from this rather long bat, I trust, not altogether unwelcome digression—since I advised my fellow tcorkeeg (as the uathor of Saturday night and Saint Monday terms his class) to make themselves clavichords, and was requested by one of tbein to furnish instructions for carrying out my recommendations, the subject has been brooding in my mind, and that being but a shallow vessel, you see, Mr. Editor, that its thoughts have run over on to thU paper, which contains, at least, ьоше suggestions how to do it. I fear my old fault of not weeing how to do a gifeat deal for a very little money yet clings to Ш'.-; and although a modern edition of а Silberman Double Clavichord would not coat quite so inneh to шике as one of Broadwuod's Iron Concert Grands, nor uuythiug lute the sum I have spent on my own experimental grand piano (which amount—being heartily ashamed of my great extravagance—I don't intend even my wife to know, lest it should become a standing reproach to me for the probably small remainder of my days) I do fear such a clavichord would cost a considerable sum to construct, for it would require to be braced considerably stronger than any ordinary grand piano. Certainly the action, excepting Lis keys, would cost but little, and its ease need not be ornamental; but then the latter may be the case with the case of a piano, some of which are not only plain, like the cooks, but downright ugly. It would also occupy considerable space, perhaps as much as a large grand sqnare piano; so all things considered, I must not boast of its cheapness in the sense of costing very little money. But, then, I utterly deny that this is the only condition of true cheapness; to me naught is really cheap which is not excellent: cheap and nasty seems to me simply a contradiction iu tenus, for the nasty in music is worse than worthless.

I am sorry I cannot yet furnish complete designs for tho construction of a clavichord. I have seen but one since I saw the two in 1882 at Messrs. Kirkman's. I am sorry to add both these are burnt. I need hardly add I have not yet attempted to make one. Were I to do so I should certainly carry out Silberman's plan, at least for two octaves in the treble. Under these circumstances it will be seen that for ше to fulfil the request of your correspondent to furnish him detailed designs would be rather a hard task. Perhaps if I cannot persuade your very practical correspondent H W. T."—who is, probably, far more able than I am to contribute a good design for a clavichord, which would have the further advantage over any design of mine of his special or professional knowledge—I may be tempted to help my fellow readers to construct old Bach's favourite keyed instrument with expression à la main. And if I do so I will embody in my design every probable improvement that my very partial and imperfect acquaintance with more than a century's experience in the construction of stringed instruments of the clavier class may suggest to me. Should a few of my supposed improvements make their appearance on the stage of public judgment in the guise of what my friend "W. T." satirically terms my crotchets, perhaps and other of my fellow-readers will bear with them as patiently as they may, in consideration that much music is largely composed of M crotchets " more harmonious than those of Тнв Hab310i<i01jö Blacksmith.

»J

BRAZILIAN KAILWAYS.

Sir,—With your permission, and in compliance with your correspondent Bernardiu's request, as contained in your journal for the 34th ult., requiring more light upon what may appear confused remarks of mine as given in reply to yonr previous correspondent (No. 3977), I do not wish it to be understood that the length I guvc us 69 miles is the actnal length of the Babia und San francisco Railway. Although your correspondent quotes an authority, yet I do not intend to accept each before my own. 1 make a kilometre to be '63,130 of a mile, but cannot allow that the above railway is near such us quoted—viz., 183*5 kilometres. Not having ever measured the distance of this line, nor hnving,asked Mr. Thompson, the superintendent at

Bahia, also not considering it worth while to go to the oihco in New Broad-street to ask Mr. W. Clay, the secretary, I am nnable to state actually the distance. The tarm, as given in iny previons answer, about it, *' beginning at a pillar and ending at a post " is one I heard applied to it there by one of its own offioiale.

Bahia is a city, not a town. The company is English principally. I could easily state mach more than your correspondent eau learn from any work that Ый- bean made up to order, and not apou the writer's experience.

Having passed some five years in the province of Bahia (principally travelling), I have stated what I know, my authority being my own senses. Trusting that these few remarks will satisfy Bernardin and yourself.

J.G.

[61

LUNA» ACTIVITY. Sin,—I have the pleasure to inclose a summary of observations of the lunar crater Plato daring April, May, and June, 1870, in which opposite effects upon certain spots are pointed out, more particularly on spots Nos. 18 and 19, not observed in April (english Mechanic, May 27, p. 3ÖÖ) and only once in May. At present the degree of visibility of these spots is very low—only *034. On the contrary, the higher visibilities of Nos. 16 and 25—'857 and '262 respectively, —strongly indicate the existence of local action of some kind in these spots.

W. It. Bibt, Cynthia Villa, Walthamstow.

SoiMAJtY Of OpeBBVATION« OV SPOTS ON PLATO—

A pan., May, Ano June, 1870.—Br W. R. Biet,
F.ll.KS.

The Липе lunation having been very unfavourable for observations on the physical aspect of the moon's surface, the returns are inadequate to determine with the necessary degree el accuracy the gradations of visibility of the bpots un the iloor of Plato. The number of observations amount to ¡16 of nine spots out of the 36 now known j nevertheless, they may be combined with the observations of April and May; tbe number in April amounting to 11ч of 17 »pots, and in May to 111 of 28 spot«. /

Tho entiru number of spota observed in the three lunations is 39, of which fuur only—Nos. 1, 8,4, and 17— were recorded by fourobscrvir-., Messrs. Gledhill, Elger, Pratt, and Whitley. No. G was seen by the three -.'.iitlemen who«? иатеь stund nrst. Eight spots were noticed by two observers—not in all instances by the нате two—and no less than 17 were seen by one observer only—the observer,as in the case just mentioned, not being the same in every instance.

As may be expected from the unpropitious state of our own atmosphere during June, the average number of spots seen on any one occasion in that month was as low as 5, and not more than 6'29 for the three months. Excluding spot No. 1 (the standard) and No. 86 (the spot discovered by Mr. Gledhill in April last) we have 28 exhibiting variations from the annnal visibility given in the Monthly Notices of the Royal Astronomical Society, Vol. XXX., p. 161. The greatest number (18) have manifested a decrease not by any means trf a regular character, or of nearly similar degrees, which, if the decrease of visibility had depended solely npon a deteriorated state of our own atmosphere, ought to have obtained. The small variation of many of the 18 spots may fairly be attributed to this cause; there are, however, six instances in which the decrease is greater than '100, spots Nos. 18 and 19 having varied as much as '245 and '286 respectively.

It was noticed in the paper communicated to the Boyal Astronomical Society, and to which reference has already been made as above, that spot No. 19 exhibited the largest decrease of visibility in the six lunations, Oct., i860 to March, 1870. This decrease was as muck as '674 below the degree determined between April and Sept. 1869. It is now '266 lower than the annual degree of visibility determined in March, 1870. No. 13, a neighbouring spot, has participated iu this decrease next to No. 19: its variation from the degree of visibility for the first six months was '316: it is now lower than No. 19—viz., '245. It is noteworthy that these spots are situated upon a light band or streak in the N.W. part of Plato tsee diagram in the Student, April, 1870, p. 101 j. The neighbouring spot, No. 16, on the same streak, has not continued to participate in this decrease: although at first it declined in visibility as well as Nos. 13 and 19, it has during the last three lunations incrensed, and was observed during the unfavourable month of June. These facts appear to be incompatible with the supposition that apparent changes on tho moon's surface depend upon changes in the direction of the sun's light apon objects, or on alterations of the angles in which the sun's rays from them meet the eyes of observers.

Ten spots have exhibited during the three lunations an increate of visibility which is irreconcilable with the idea that the larger decrease during the same period is entirely dae to a deteriorated terrestrial atmosphere. The greatest increase, '177, occurs in the spot No. 25, discovered by Mr. Elger, on October 18th, 1869, and subsequently observed by Messrs. Gledhill and Pratt. The increase or decrease of visibility of a spot doee not necessarily iudicute, after a certain epoch, either я present or continued change in the spot itself; for as the determinations are comparative, an actual change in the spot rendering ft, for example, "brighter," and consequently more readily seen, its visibility during the time its brightness continues would rise, and it* higher degree of visibility, so long as it was maintained, would, to a certain extent, measnre the duration of its maximum, to borrow an illustration from the phenomena of variable stars; but when this brightness subsided, aud during the time the spot remained at Its minimum, it would be seen only on very favourable occasions, and its degree of visibility would fall and oscillate within certain limits, dependent in such a case on the state of the earth's atmosphere.

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SPECIMENS OF TURNED WORK.

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SPECIMENS OF TURNED WORK.

Sir,—I beg to send you photographs of some of my "turned work," which I hope will reach you safely. I much regret you havo not received them long ere this, but I have been prevented doing any photographic work until last week.

J. H. MuBOAX.

Parklands, Clifton, June '23.

ra

READINGS FROM THE GLOBES.—VI.

Sie,—As our object is to illustrate, and these readings are intended not for the mathematician, but chiefly for those whose pursuits prevent them from studying spherical trigonometry from the works of Vince, Hymer, Todhunter, and others, it may be as well for us, before proceeding farther, to see if we have clear notions of what a spherical triangle is; as without them we are liable to get into confusion on such subjects. We have not the intention (and if we had our Editor would object) to introduce long demonstrations by lines, tangents, and cosines, but to show how even anyone who attends can obtain some ideas of spherical trigonometry, even by studying a globe only; and in fact if we have not access to a celestial globe, everyone knows what a cricket ball is, and he may even by making marks upon that understand something about it. Of course we know that accuracy is the order of the day, and we cannot be thoroughly accurate without forroulje, but these remarks may possibly serve as an introduction to some who may hereafter become eminent in this branch of study.

First we shall inquire what a spherical triangle is, [2] state what is meant by the pole of a circle, [8] show how a spherical triangle may be measured when it is made on a globe. A spherical triangle is made by great circles on the surface of a sphere, and not by small circles. Thus, referring to a globe or even a map of the world, we shall see that all the parallels of latitude are small circles, because, if the globe were cut through on these marks it would not be divided into two equal parts, but if cut throgh where a great circle is, at the equator, ecliptic, or the meridians which pass through the poles, it would then be divided into two equal parts. Where then three great circles cut one another they will form a spherical triangle. Thus, on the globe the elliptic cnts the equator and forms an angle, the meridians cut the equator and ecliptic and form angles and Rides ; and this i, where the distinction lies, in the sides not being straight lines but arcs of circles, of greater or less measure, as it may happen. Then again, when wo turn a globe it spins on its axis, and the extremities of the axis are called poles, from a Greek word signifying to tain. Now these poles—namely, the north and south poles on a terrestrial globe, are the poles of the equator, and every great circle on a sphere has the pole round

which it would spin. Thus the pole of the ecliptic has a different pole from the pole of the equator, and if we wished to find the pole of a meridian line, wel must measure 90- distance from that circle in order to find it, and we must thoroughly understand this before we venture far upon the wide ocean, whether of investigation or commerce, and in fact it is most necessary for a nautical man to be acquainted with this subject, as upon his knowledge the lives of his fellow passengers may depend. Thus, in Fig. 1, let A B C be a right

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angled spherical triangle, then the point A, being 90° from the arc B С, is the pole of the circle of which А С is on arc, and in like manner C is the pole of the circle of which A B is an arc, and we must always go to the poles of the arcs to measnre epherical angles. It will be clear by inspecting the figure, that a spherical triangle may have more than two right angles. Euclid tells us that the three angles of every triangle are equal to two right angles, but this applies' to plain triangles only, and not to spherical triangles, for by a globe it is easy to see that there may be three right angles in a spherical triangle, for if the angle A be situated at the pole in a parallel sphere, it will be measured by the wooden horizon and will be found to be 90:, the angle С would be at the east point of the horizon, and would be measured by the brazen meridian, and the angle B could be measured by the quadrant of altitude. If again we have an oblique angled spherical triangle how must we measure the angle B A C ; we must not measure it by the arc B С, which is 80', but we must measure it by the arc D E. The arc B C is one of the sides, but not the measure of the angle at A. We must go to the point D, just 90° distant from the point A, or we must find the arc of which A is the pole, and the width of this arc will be the measure of the luiglo A; and we must proceed in the same way with regard te the angles B and C, then we shall be able to tell whether they are oblibue or right angled. In fact all the cases of spherical triangles may be solved by means of the globe, and if when working by the formula; we are in doubt as to the result, we may obtain an answer approximately by forming the triangle with prepared chalk, so as not to injure the globe, on its surface. This method will not by any means supersede the use of mathematics, but by using both methods together we may generally obtain accurate answers.

T. S. H. P.S.—Upon further trial, I make the distance from

Cape Horn to Good Hope 4,0
from Good Hope to Port Jock
miles, and from Port Jackson
Horn 6,827 miles, which very nearly cor-
respond with " M. L.'s " result.

19]

SHORTHAND.

Sut,—I feel it my duty to remark upon the description of Pitman's shorthand given by Mr. F. W. Griorson, on page 826. I am a writer of that system, and by several remarks made by' the above named gentleman, I con only conclude that he, when learning Pitman's Phonography, must have goue contrary to the directions given by the inventor. Mr. Grierson has learned th.,, systems, at times sufficiently far щ,лП as not to mix one system with another. I can speak from experience on Pitman's alone, as I never saw the other two.

Mr. Pitman advises no one to write quickly until he is able to write well. Speed will be attained by practice. Mr Onerson says the great fault in Pitman s consists in using the same charoetere when made thick and thin to represent different letters. Here he is in eü°r' ... one iB maae tbici and the other thin, they cannot be the same character. For instance, the letter " n" is rotom the slanting position from left to right, thin, the thick form in the same direction being the representative of • "»»HbepeTcci'-ed that there is as much similarity in the prononnciation of the two letters ы there is in the appearance of their respective phonograms. Mr. Grierson proceeds to say that " the consequence of this similarity is, that unless the subject is transcribed while it is fresh on the memory it i* practically illegible." Here he is again labouring under a delusion. I have transcribe? reports of speeches, 4c., both of niv own and others' reporting, several months after being written, with the most perfect ease, and some of the subjects I had not previously seen -, and it is a rare oc=— currence indeed that a letter is written thick instead of thin, and even in a solitary case of this kind the difficulty is soon solved, for if a letter should, by accident, be written thus, it merely alters the sound from "p" to "b"—the word " paper" would read ** paper," 11 perfect "" perfect," Ac., and the error is at once detected. Mr. Grierson's remarks upon the vowels and diphthongs, as being the most ridiculous feature of Pitman's shorthand, is in my opinion about the most ridiculous idea he has favoured us with. (See lines 88 to 25 from bottom, page 828.) There are, as he says, no less than six different positions for the vowels, but each Towel is always in the same position ; and in the case of a f -reign word, requiring insertion of vowels, it requires IE. more time for the "considerations" he speaks of (in the lines just referred to) than it takes an ordinary huighand writer, when about to write the word " Grierson," to think how to make the capital G, where to commence making it, and, after having written it, to turn back (and take his pen with him) for the purpose of dotting the " i." If he had to make out a table, iu order to remember the positions of the vowels, Ac., it is evident that he had not learnt them properly, and Pitman's explicit directions are not to leave one page until you thoroughly understand it.

Anything can be read in twenty or thirty years hence w-ithontfdifficnltytin Pitman's system, unless there are improvements added. Additional improvements are quite possible, as I hare no doubt is the case with Lewis's, although it has undergone improvements for the last forty years. The art of joining several words together is an advantage of Pitman's over most others. In some cases nearly a dozen words may be written without lifting the pen, although only three or four are generally used. I think there is no advantage in having short hand for figures, as the present system of numeration is calculated to be quite equal to our utterance, especially when there are more than six figures.

Mr. Pitman publishes his teacher at sixpence, while Mr. Lewis's is ten and sixpence. Does Mr. Grierson supply this information for the choice of his readers, or does he think that the systems are to be compared to each other in value, in accordance with the price? He has one advantage over me. He says "only those who speak from experience ought to express an opinion on the relative values of various systems." I may say, however, as one having considerable experience in Pitman's system, if his experience in Lewis's is not better grounded than it was in Pitman's, I am afraid he won't make much at it. If his "advantages" of Lewis's system are as much exaggerated as the "disadvantages" of Pitman's are in his description (without wishing in the least to hurt his feelings), I would not give half a guinea for all the shorthand books Mr. Lewis has in his possession.

Wm. F. Mom I v

[We have received several other letters in answer to Mr. Grierson, and written pretty much in the same strain as the above. We should like to have inserted those sent by " W.," "J. R.," and " An Experienced Hand," but space forbids- Ed. E. M.]

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