[3965.]-ORGANS.-Will the "Harmonious Black smith,' Adept," or any of your organised body of contributors give me some information on the following subject: When my organ was built some years since, funds being rather low, about six or seven of the bottom keys in the swell were left minus any pipes. A few months ago I consulted a first-class organ builder on the subject of having pipes attached Ho examined it, and informed me that the swell box

had just been made to encase what pipes there is in,
and no more; and that if I wanted pipes attaching
they would have to be placed outside the case, a piece
of business my swellish pride objects to.
Will any
rother reader (or sister either) give me their kind
suggestion ?-THE HARMONIOUS COTTON SPINNER.
[3936]-TABLES WITHOUT DECIMALS.-I am of
opinion that for certain practical and common pur-
poses all tables which can admit of figures-without
minute decimals-would be a boon to numbers of
working mechanics and others not having the power

METHOD FOR RENDERING WOOD DIFFI-
ING IT WHEN UNDERGROUND.-Dr. Reinsch re-

of making calculations; and I know of no medium CULTLY COMBUSTIBLE, AND FOR PRESERV- offered its gold medal (of the value of 21 guineas) for

condenser?-R.W.

[8967.]-MAGNETIC NEEDLE.-Will any of your subscribers answer me this question:-Supposing I have two magnetic needles centered, one strongly magnetised and the other only faintly so, from which ought I to get greatest deflection, placing each in successien in the same coil-Onra

A

Some

the blade of the bradawl in such a manner that, machinery constantly exposed to friction. The grease when the blade is inserted in the busk, the nozzle thus obtained forms an excellent tallow, burning with or screwed cap may be passed over such blade, and a clear, brilliant, and what is infinitely more to the may, when screwed up or home on the busk, abut purpose, a white light, and at the same time emitting against a corresponding projection-collar on the not a trace of any unpleasant odour, or of the ordinary blade of the bradawl formed for the purpose, and disagreeable accompaniment of combustion-smoke.made to fit in such a nozzle or cap. "Notes and Queries on China and Japan." WARMING CARRIAGES.-A new method of EXHIBITION OF FANS,-At the South Kensingwarming first-class carriages in express trains has ton Museum there has been opened to the public an been adopted in Bavaria. A special van is attached exhibition of fans. The exhibition is a part of the to the train, and contains a powerful "calorifere," scheme of the Department of Science and Art for the and the heated air is conveyed to all the carriages art instruction of women. To promote this object, of the train by means of india-rubber tubes. The the Deparment offered prizes in competition for fans experiment with first-class carriages is reported painted by the students in the female schools of art in upon so favourably that the authorities have deter-1868, and again in 1869. The fan-mount to which in mined to apply it to all the carriages on the the first of these years the chief prize was awarded, is Bavarian lines, and it is expected that it will soon included in this exhibition, and it is intended to conbe adopted on all the German railways. tinue the competition. Her Majesty also purposes to offer a fan prize for competition at the International Exhibition of 1871. The Society of Arts has also equal to the ENGLISH MECHANIC to start the system. the second-best fan exhibited. The Lady Cornelia Will any brother reader kindly arrange a table-free commends the following:-The wood, which must not Guest and Baroness Meyer de Rothschild have each from decimals-giving the quantities of water, in be planed, is placed for 24 hours in a liquid composed offered a prize of £10 for the two next best fans. pounds, ounces, and parts of ounces (of course avoir- of 1 part of concentrated silicate of potassa and 3 of pure water. After having been removed from this sum of £50 will be awarded and spent in various dupois), required to condense a cubic foot of steam, so amounts by the Science aud Art Department, for fans as to produce a practical working vacuum, the steam liquid, and dried for several days, the wood is again produced by female students of the schools of art in to increase from common atmospheric pressure to 1lb. soaked in this liquid, and, after having been again the United Kingdom. Among the more curious of the per square inch, up to 101b., or upwards, with size of dried, painted over with a mixture of 1 part of cement fans exhibited is one dated 1650, the mount of which and 4 parts of the liquid above alluded to. After the is a landscape and figures embroidered in silk. first coat of this paint is dry, the painting is repeated of the carving of the mounts is exceedingly delicate twice. Of the paint-mixture alluded to, large quan- A fan, one of the wedding presents of the Empress of tities should not be made up at once, because it rapidly the French, is especially noticeable for its display of becomes very dry and hard. Wood thus treated is rendered uninflammable, and does not decay underfine open cutting in so brittle a material as mother-o'pearl. Some of the fans possess historic interest, two ground. or three being associated with the unfortunate Marie Antoinette. The Queen contributes sixteen examples; the Empress of the French, thirty-five; and the Princess of Wales, Princess Christian, and Madame la Comtesse de Paris, are among the contributors. SCRAPING SLIDE VALVES.-Mr. W. P Cowan, American of Brooklyn, New York, writes to the "Scientific to the effect that few workmen know how to scrape properly. He says:-I have always found the scraper works best after a smooth file; everything should be finished with the smooth file previous to the scraper being used. I have seen many workmen leave too much to be done by the scraper. Now that is a gross mistake; every article ought to be fitted as well as possible before being touched by a scraper; otherwise a bad job is almost certain to be the result. marks, never across, at any rate. Nothing makes a scraper should always be used obliquely to the file better scraper for wrought aud cast iron than a taper saw file, and for brass a flat scraper must be used if good work is wanted; say about lin. broad and 5-32in. thick. A saw file scraper is too keen for brass. scraped slide valves, motion bars and blocks, and axle is much used, and with the best results. We always boxes. It is certainly a very unworkmanlike way of turning out a slide valve and leaving it to work itself tight. It is tantamount to saying it can't be made tight. Most of the first-class marine engine builders in Great Britain scrape valves, &c. In one case last year it was tried to do away with the scraper on a pair of large valves; but on the trial trip the valves got cut up awfully, so scraping is considered a necessity.

[3968.]—KILN.—Will one of your correspondents oblige me with a description of a good kiln for burning lime, and state the proportion of coal used to lime burnt, also the quantity burned per day? A sketch would be useful. Is there any good practical book on the subject?-L. M.

[3969.]-COPPER BOILER.-Can any of my brother readers kindly inform me of the most efficient design of copper boiler to drive an iron boat 66 inches long by 6 inches beam, the engines of which are two cylinders, each 14 inch bore and 19 inch stroke; and what would be the best form of apparatus and fuel for firing same. The boat is 6 inches deep ?-O. G.

[3970.]-FOOD FOR COWS.-Will any reader tell me how to steam food for cows; to do fifty bushels at once. Would it be cheaper to have an iron tank or brick and cement tank?-R.R.

The

[3971.]-DISPLACEMENT OF SHIPS.-Will any of our correspondents be so kind as to give me a proper way to find the displacement of a ship? I getting; for there are poor as well as good kinds. In all railway shops in the north of England scraping have not given any dimensions, but those that can do it, can take a length, breadth, and depth for themselves. I know that it is a difficult problem, but surely there is one amongst our talented brothers that can assist me.-G. B. D.

USEFUL AND SCIENTIFIC NOTES.

HACKNEY SCIENTIFIC ASSO CIATION.-Mr. H. W. Emon, the Hon. Sec. of this Institution has sent us a report of its third annual meeting just held, from which we gather that the institution is flourishing. The number of members was actually twice as great as at the commencement; the papers, &c., read had been more interesting and numerous than on any previous occasion, and the library, which had only been commenced this year, already comprised many valuable works. The conversazione, held at the commencement of the session, was attended by a much larger number than was expected. It was announced that during the summer months excursions would be organised to places of scientific interest, also to the various public museums.

SOME HINTS ABOUT SCREWS.-Where screws are driven into soft wood and subjected to considerable strain, they are very likely to work loose; and it is often difficult to make them hold. In such cases, says the Canadian Builder, we have always found the use of glue profitable. Prepare the glue thick; immerse a stick about half the size of the screw and put it into the hole; then immerse the screw, and drive it home as quickly as possible. When there is an article of furniture to be hastily repaired, and no glue is to be had handily, insert the stick, fill the rest of the cavity with pulverised resin, then heat the screw sufficient to melt the resin as it is driven in. Chairs, tables, lounges, &c., are continually getting out of order in every house; and the proper time to prepare them is when first noticed. If neglected the matter grows still worse, and finally results in laying by the article of furniture as worthless. Where screws are driven into wood for temporary purposes they can be removed much easier by dipping them in oil before inserting. When buying screws notice what you are See that the heads are sound and well cut; that there are no flaws in the body or thread part, and that they have gimlet points. A screw of good make will drive into oak as easy as others into pine, and will endure having twice the force brought against it. CHANGES IN FISHES.-In the American Naturalist, Charles C. Abbott, M.D., gives some account of the changes in the fishes of New Jersey within a few years. A slight local disturbance quite alters the fauna. Thus in 1867 a small, never-failing brook, emptying into the Assumpink, was populated by chubs, dace, and minnows. In July a heavy, sudden fall of rain caused a rise of water but did not alter the brook enough to attract the attention of those who lived near it. After the subsidence of the water not one of these fish could be found there, while their place was taken by roach, mullets, and red-fins, which are now abundant, while not a chub can be found. Dr. Abbott the New Jersey streams twenty-five years ago, which are now quite abundant; and he is greatly at a loss to imagine how they can have reached these streams. He mentions the interesting case of the gizard shad, which is sometimes carried by freshets into inland streams or ponds. A pond near Trenton was stocked with them in 1857, and is now full of specimens, weighing sometimes five pounds. They have become so different in colour from the same fish as found in the Delaware and on the cost, that Dr. Abbott at first thought them quito distinct and he says they have changed considerably, but only in colour, during the last ten years.

mentions several fishes that were not inhabitants of

GRAFTING IN CHINA.-A very peculiar method shoots of the chrysanthemum are inserted into the of grafting is practised in China. In spring the young cision, cross shaped, in the stem of the latter, and stalk of the aia plant (wormwood ?), by making an inbinding the two tightly together with a piece of past or hemp. After the incision has been properly bandaged; a flower-pot is put over it, bottom downwards, the plant passing through the hole in the pot, which does under it, about six inches high. Earth is then put into not rest on the ground, but upon four bricks placed the pot, and the plants gradually unite, taking root at the same time in the pot. As soon as the chrysanthemum flowers, the stem of the ai is severed immediately under the pot, and the whole is removed from the nursery to the garden or verandah. The grafting strengthens " the chrysanthemum, which would otherwise produce but a very poor flower. method is most ingenious, and the plants seem to unite very readily.-Notes and Queries on China aud Japan.

The

REFLECTED LIGHT.-A series of experiments with a novel form of apparatus for determining the amount of light reflected from metallic surfaces at different angles has shown Professor Rood that a mirror silvered by Liebig's process, using the silver side at an angle of 45 deg., reflects 91 per cent. of the light emitted by a flame, and from the glass side 78 per cent., while an amalgam mirror at the same angle reflects only 455 per cent. The apparatus and method employed will be found described in the "Journal of Gas Lighting, &c." It would be interesting to know the reflecting power of the beautiful platinised mirrors now coming into use.

A NEW PROJECTILE.-Captain Ericsson announces, in a communication to the American Army and Nary Journal, that he has perfected a system of sub marine attack by which he can destroy the largest ironclads ever built. The resistance of the water is so great that explosive projectiles have always proved DEEP-SEA DREDGING.-The Admiralty have failures hitherto when designed to strike below the acceded to the request of the Royal Society by again water-line. Captain Ericsson is confident that he has placing Her Majesty's surveying steam-vessel the devised a projectile which will overcome the difficulty Porcupine at their disposal for another deep-sea caused by this resistance. It is an elongated shell, exploration, to commence in the latter part of June. charged with 300lb. of dynamite, and shot from a 15in. Mr. J. Gwyn Jeffreys wil take charge of the first gun, at such an elevation as to enter the water near the cruise, which is intended to be across the Bay of hostile vessel, and strike the hull anywhere below the Biscay, along the coasts of Spain and Portugal, to water-line. It is fitted with a percussion cap, which Gibraltar. Dr. Carpenter will there succeed him in explodes upon very slight impact against the hull, so the beginning of August, and proceed into the Mediterthat the velocity of the shell when it reaches its desti-ranean, after endeavouring to trace the direction and nation need not be high. The gun is carried on a nature of the currents at the Straits. Professor swift armoured boat, protected by a turret. Captain Wyville Thomson will probably join Mr. Jeffreys. A Ericsson intends to make a formal offer to test this in- photometric apparatus has been contrived by Mr. MILK-It may be worth mentioning, for the sake vention. He is ready to fit out, at his own cost and Siemens for the purpose of ascertaining the depth to of people employed in white lead works, and other risk, a fast screw vessel, with two 15in. guns of the which solar light penetrates the sea; and other ques-occupations which expose them to the same risk, that kind described, if somebody else will furnish the ironclads to be experimented upon. In the politest terms he does this country the honour to single out the new British nelad Devastation as one of the most splendid pecimens of an armoured war-vessel which can be produced, and challenges her to come out and encounter his torpedo.

BRADAWLS-It is stated, remarks the Scientific Review, that there are but three bradawl makers in London, and a bradawl seems to offer such a small field for improvement that a patent would appear to be scarcely worth applying for; yet this is not the case. An improvement has been invented, which consists in making the busk in two pieces, one secured to the handle, and having thereon a tapped or otherwise formed upper part, made to fit in and correspond with the second piece, such second piece being a tapped or otherwise formed cap, furnished with an internal projecting collar or shoulder, both pieces being constructed to receive

tions of considerable interest will be investigated iu
this expedition. But we regret to find that the time
is so limited for such an important object.

THE GREASE TREE.-In China there grows a
tree known as the Grease Tree. It is said that large
forests of this vegetable lubricant are to be found
there, and they form the source of a considerable local
traffic, This tree not very long ago was imported
into India, and it is said that the experiment of cul-
tivating it there has proved quite successful. In the
Punjaub, and North-western provinces generally, it
grows as rapidly and as vigorously as in its native
soil, and there are already thousands of t ees on the
government plantations yielding tons of seed, ad-
mirably adapted to a variety of commercial purposes.
Dr. Jameson, a chemist in the Punjaub, has prepared
hundred weights of grease from this particular tree;
and has forwarded on trial a portion of it to the
Punjaub Railway to have its qualities tested in a prac-
tical manner as lubricating material for those parts of

milk taken as a drink has been found as useful as the dilute sulphuric acid in preventing colic.

GLUE-The value of glue, that is, the amount of pure gelatine it may contain, may be determined by precipitating this body with pernitrate of mercury, a standard solution of which tested with a kuown weight of pure gelatine may be employed.

FIGURE OF THE EARTH.-Mr. Jas. Beardsley has written us a long letter, which may be summarised in a few sentences. He disclaims any connection with "Parallax," Mr. Hamp-provements in the machines for and the manufacture of den, or Mr. Carpenter, as he knows nothing of them, and and has not read anything they have written. Mr. Beardsley thinks that as he is honest and independent in the utterance of his opinions, he is entitled to a fair answer, and not misrepresentation or abuse. He considered it a pleasure to hold communion with such a correspondent as Mr. Tydeman, "who calls in question my sentiments in a charitable and concise manner, without rancour and without abuse."

The English Mechanic

AND

MIRROR OF SCIENCE AND ART.
FRIDAY, JUNE 10, 1870.

FOR

NOTICE.

external boundaries of luminous surfaces which being incalculably more feeble than the intrinsic answer the description as far as one side of them splendour of stars of any considerable magnitude. is concerned. The surface itself mathematically I have, however, noticed a border round the limb represented by an infinite number of points, will of Venus, undoubtedly due to such a cause, and produce a luminous image composed of an in- in all probability it would be very conspicuous finite number of overlapping spurious discs; and round the sun, were it possible to view him withthe outer boundary which terminates that surface out such a darkening apparatus as must extinwill consist of the half of such an image of a line guish all such appendages. The knowledge of as has been described; the other half being of these facts serves to explain why the details of course merged in the general illumination of the planetary surfaces are frequently not so well disc. Every line being referable to an infinite made out with the largest apertures as we might number of points, and every surface to an infinite have beforehand expected. The amount of light OR years past the ENGLISH MECHANIC,though number of lines, and the image of a luminous may be sufficient to render the interference-rings professing to be published on each Friday point being strictly ascertainable as to character visible, which, overlapping each other throughout morning, has in reality been published on the pre- by the laws of optics, and determined as to the luminous area. must produce a certain magnitude by the experience of the best opti- amount of hazy indistinctness, or what is comeeding Monday. We have, therefore, been obliged cians, we have at length a clue which will guide monly termed a "glare." Hence there is often to go to press on Friday evenings, or a week before us through all the details of telescopic definition. a gain in the definition of minute details by the the nominal day of publication. As this arrange- which must be carefully borne in mind. The haze, and this may probably be the reason why are, however, collateral considerations reduction of light through moonlight, twilight, or ment has occasioned no end of inconvenience to phenomenon is not only objective but subjective every telescope usually shows such details best correspondents and advertisers, it has been deter--that is, it depends not merely on the existence with a certain amount of power-namely, that mined in future to go to press on Tuesday evenings, retina to appreciate them. of certain undulations, but in the capacity of the which without expanding the light to too great Below a certain in- feebleness, reduces it so far as to render these and publish early on Friday mornings; in other tensity, varying considerably in different in- rings, and the resulting irradiation or glare, inwords, on and after the 8th of July next, the dividuals, the vibrations constituting light fail to sensible. produce any perceptible effect upon the organs of ENGLISH MECHANIC AND MIRROR OF SCIENCE vision; and the office of the telescope in many will be published at the same time as the widely- cases is, by collecting a greater number of these circulated London weekly papers. In order that vibrations, to produce the requisite intensity, and to strengthen the latent image till it excites the no inconvenience or disappointment may arise, retina to a sufficient degree. Thus, though the our readers will oblige us by informing their optical image of every star is theroretically surrounded with a considerable number of rings, respective booksellers or newsagents of the con- in practice our eyes can only distinguish a few of ELECTRICITY-ITS THEORY, SOURCES, templated alteration in the day of publication.

We beg also to inform our Subscribers that we have purchased the copyright of Scientific Opinion, and that on the day mentioned-the 8th proximo, that well known and high-class scientific publication will be incorporated with the ENGLISH MECHANIC. Scientific Opinion has a good staff of contributors and correspondents ;these, added to our own, will no doubt materially enhance the

value of the ENGLISH MECHANIC.

There

them, even around the brightest stars, from the
diminish in magnitude, so the outer rings go
rapid degradation of their light; and as the stars
successively out of sight. By the use of a larger
aperture we counteract this degradation, and
restore some of the lost rings; but as we call up,
so to speak, the rings of the inferior magnitudes,
80 we bring into sight the central discs of in-
nnmerable fainter stars, which were before im-
perceptible, and whose rings are still too feeble
for our sight. And the same of course holds good
with the external portions of the spurious discs
which are in a similar way lost sight of, or
brought into view, according to the visible
telescopic brightness of the star. In every case,
therefore, of a luminous telescopic image, the

HINTS TO ASTRONOMICAL STUDENTS. theoretical result is modified by the receptive

BY T. W. WEBB.

(Continued from page 74.)
In the vature of the images formed from
Na previous paper we discussed at some length

luminous points by refraction on reflection, and
the representation of stars by spurious discs, with
their attendant rings. We will now proceed to
extend our remarks to the consideration of the
telescopic definition of lines and surfaces. The
character of this, after what has been said, it will
not be difficult to understand. As the real discs
of the stars, from their extreme remoteness,
approximate, so far as our sight is concerned, to
mathematical points, so, for the same reason, the
natural outlines and boundaries of heavenly
bodies become sensibly mathematical lines. But
the mathematical line may be considered as com-
posed of an infinite number of mathematical
points;
and its telescopic representation will
therefore be equivalent to an infinite number of
spurious discs, each with its attendant series of
rings. The resulting image, instead of being in-
definitely and almost imperceptibly narrow, must
have a sensible breadth equal to that of the
spurious disc; and the edges of the infinitely
overlapping rings wi produce as many narrow
luminous borders on both sides of it as there are
visible rings, each parallel to the bright band
which forms the image of the line.
natural result of what we have already attempted
to explain; we have, however, no opportunity of
exemplifying it in practice, there being no in-
stance of a luminous object in the sky, at once,
long enough, narrow enough, and bright enough
to form such a telescopic image. We have, how
ever, in the limbs of the celestial bodies, the

Such is the

power of the eye, and the aperture of the instru-
ment enters materially into the result, not merely
as giving a larger or smaller spurious disc, but as
which they produce by their superposition.
making visible a greater or less number of rings,

in the case of a line, the luminous border

We are now in a position to understar.d why the outlines of every telescopic image, the limbs, for instance, of the moon and planets, though remaining perfectly distinct, in a good instrument, up to a certain degree of magnifying, with every subsequent increase of power. In become progressively less hard and cleanly-defined their own nature they are throughout only approximately sharp, being composed of an infinite number of overlapping external halves of spurious discs, whose light decreases rapidly towards their edges. As long, however, as the magnitude to the radius of the disc, or at any power employed is insufficient to give a sensible rate to the portion of it where the light sensibly fades, so long the sharpness of outline continues apparently perfect, whatever eyepiece may be employed; but under the same conditions of magnifying which render the spurious disc large enough to affect the eye with the idea of size, we shall find the hard definition of outlines begin to fail. Theoretically considered, the latter composed only of semi-discs, should bear twice the amount of power with equal distinctness; but these are niceties into which we need not enter. We may however remark, what is fully planetary definition always is in proportion to borne out in practice, that the sharpness of the size of the telescope, the diameters of the spurious discs on which it depends varying inversely with the aperture. At first sight it might appear strange that we do not see the limbs of the moon and planets attended by a border resulting from the presence of, at least, the first interference-ring, and that the details of their surfes are not rendered indistinct from the same cause, but a little consideration will show reason that rings are not noticed round the that such an effect is imperceptible for the same smaller stars-namely, the want of intensity of light, the reflected lunar and plar etary beams

as

We have thus pursued the subject of definition to a considerable extent. The different modes, however, in which telescopic vision may be effected will render a little further investigation necessary at a future opportunity.

130.

AND APPLICATION.

BY J. T. SPRAGUE.*
(Continued from page 218.)

The next great class of electric generators includes nearly all the other forms of battery. The principle is the employment at the negative plate of some substance containing oxygen in such a condition as to be readily parted with; thus the hydrogen instead of being set free, decomposes this substance, forming water; he ingenuity of inventors has been largely exercised in varying-1st, the negative plate; 2nd, the oxidising agent, this latter being either liquid or solid. By keeping this classification in view, the principles and qualities of the different forms are rendered much more comprehensible than by a mere description of successive

inventions.

131. GROVES'S CELL.-This was the first devised

of this class, and in most respects is the best, platinum being the negative metal, and nitric acid the oxidising agent. The form is not essential, but it is usually made with flat plates; the platinum in a flat and narrow porous vessel to reduce the in two plates connected together, or one plate quantity of acid to the least, the zinc being either bent so as to surround the porous vessel at a distance of about three eighths of an inch. Fig. 40

cylindrical porous jar, as in Fig. 41, which will serve as the type of this form.

39 and thereabouts, is double aquafortis, and about 63 is single aquafortis.

of

by one atom of acid would be different. The 28, is 2HNO3 + 3HO. This is the strength principal action which really occurs is the first to which boiling brings both stronger and weaker 133. CARBONS.-The employment of carbon is and third combined, HNO3 + Hs becoming acids and distils unchanged at 248° Fah., but is attended with some difficulties which call for at-2 H, O + NO, and according to this, one atom of not, as sometimes stated, a definite hydrate, as it tention here. Carbon is one of the most remark- nitric acid is effective for one and a half equiva-varies according to the pressure. able of the elements, possessing what is called lents of electrical action; or to express it practi"allotropic" forms, in which, though chemically cally, though not in the true chemical language, the same thing, its physical properties are dif- two-thirds of an atom is the equivalent. This ferent, with different relations to heat, electricity, action is however complicated with others, for and light; such varieties are the diamond, char- the acid is even totally deoxidised and converted coal, and graphite. It is this latter which is useful into ammonia to some slight extent. Owing to in electricity, either in its natural form of plum- this and to the loss by evaporation or carrying bago or black lead, or the artificial deposit of gas away of acid by the escaping gases, and by carbon. It must be clearly understood that this leakage through the porous cell, the working substance is not coke; coke is the solid residue equivalent or value of the acid can only be settled left after distilling coal; the graphite comes from by actual experiment, and in addition to this, the gas, the rich hydrocarbons of which are de- when we buy nitric acid we only get a solution of composed by contact with the heated retort, on it varying very much in actual strengh. I therewhich they form a shell; it is, in fact, a great fore have calculated a table showing the pronuisance to the gas maker, as it arises from the perties of the acid at the various strengths; it is destruction of the richest gas, injures the retorts, not prepared for analytical, but for practical use, and wastes the heat; in the gasworks it is called and is based on Ure's tables. Column I. is the "scurfing." The densest and hardest is the best specific gravity as given by him; Column II. is for electrical use, and some which comes from the percentage of true acid HNO U e's tables abroad is far superior to anything our English are based on the anhydride N, O, formerly recals produce; it should be almost non-absorbent, garded as the acid, but I have calculated the and ring like a metal when struck, and have a true acid from his figures. Column III. is the clear gray colour, not black. It is rather costly number of atoms of 63 grains weight contained when good, simply because of the great difficulty in one lb weight; 'and Column IV. the number of working it. Other substances will answer, of those atoms in 1000 grains fluid measure; such as the material of black lead crucibles, which these two I have calculated from the percentage, is indeed made up for the purpose, and they will furnish every required information as to the work which acid of any strength is equal to.

The chief difficulty with carbon is making the connection with it; this is commonly done by simply fixing a clamp on it, in which case a piece of platinum ought to be interposed between the two surfaces. A better plan is to deposit copper on the upper part, and then solder the connection to it, as this gives continuous circuit; the copper takes on it just as it would on a metal. There is one drawback to this, the same in fact which requires the platinum interposed in the first plan; the acid both creeps up the surface and soaks into the substance, and then acts on the copper and destroys the connection. I have devised a perfect remedy for this which I do not think has ever yet been published. Before use I thoroughly dry the carbon and mark on it the point to which the liquid will reach, and then moisten with water this part, and also the extreme top where the copper is to go; the intermediate part is then heated by a Bunsen's gas burner, and touched carefully with a piece of paraffin as long as it will absorb any, taking care none runs over the surfaces to be used; with care this intermediate portion may be thus thoroughly saturated with paraffin, which resists contact of liquids, 21 and on which acids have no action; the copper is now deposited, and the connection fixed, and then the copper surface and top of the carbon is covered with a thick coat of paraffin, which serves as a complete protection.

136. The following experiments will both illustrate the uses of the table and the actions of the battery. The acid used was pure, intended for analytical purposes, its specific gravity 1-3175 giving, by averages between No. 49 and 50 in the table, a value of 10-58 atoms per 1000 grains, or 5.29 for 500, the quantity used in the porous cell, which on the above theoretical considerations should furnish at two-thirds 7·93 equivalents; 3000 grains measure sulphuric acid solution were used in the outer cell equivalent to the consumption of 12 units of zinc, and a sheet of copper was arranged to receive a deposit of copper. The cell continued in action for nearly 7 hours, giving a deflection ranging between 67° to 55° and at last falling rapidly to 20°. There were deposited 8.64 units of copper, while 10-21 units of zinc were dissolved, showing a loss, by local action, of 1.57 units. I afterwards allowed the action to go on as long as any took place, but only 1-23 more of copper was deposited, and 3 of zinc dissolved, showing how much the local action increases towards the end; it was more than 14 per cent. beyond the 5 allowed in calculations for the simple cell: as to the nitric acid, 8-64 the true work is so near 7.93 that calculated as to show that the reaction described is the chief one and that the more perfect deoxidisation which may occur compensates for losses; however as it is not possible to work to near exhaustion as in this experiment, for practical purposes the atom should be taken as the equivalent instead of two-thirds.

137. It has been recommended to use salt instead of sulphuric acid, and the following trial was made under exactly the same conditions as the first; the current went up to 64 lasted 3 hours instead of 7 gave a deposit of copper 4:13 units and use of zinc 472 being a loss of oneeighth by local action. This proves, as might be expected, that the use of salt is bad economy, it takes no part in the reaction (so far as cost is concerned), except as a conductor, but the zinc is dissolved by the nitric acid transferred to it by electrolysis.

138. For practical use a much cheaper nitric acid may be obtained. Thus I use one of sp. gr. 1:4146 containing 76-4 atoms per lb., and costing threepence per lb., or '0393 of a penny per atom. Applying the results of the experiment to this value we have the cost of working nitric acid batteries thus:

Atoms
per lb.

1:5210

100

111-11

214

1.5009

92-978

103:31

21.5

1.1980

92048

102-28

21.39

1:4960

91-115

101-12

1:4940

90-189

100-21

134. Other materials have been employed, as lead or iron, platinised. Cast iron has been strongly advocated under the name of Callan's, or the Maynooth cell; a very few words will sum up their qualities. They are worthless. If any one wishes to lose his temper and his money he can use a cast iron battery, with some certainty of success. They waste the acid frightfully, they boil over suddenly, in fact they do everything we 39 should wish not done, without having one redeeming quality to atone for their evils.

77.78

15.78

135. The relative merits of platinum and carbon depend on circumstances; the first is most expensive at first (especially as it is bad economy to use very thin sheet, which is a bad conductor, and soon becomes brittle and breaks up), but it gives a slightly higher force, and is preferable if the battery is to be much used. Still, for ordinary use the carbon answers every purpose, and is much more commonly employed. The actual conditions and expenses of working are the same with both, and the following remarks apply to both, though the experiments were actually made with a carbon plate.

It is impossible to give an exact statement of the reactions which take place in the nitric acid cell, as they are continually varying with the strength of the acid. HNO3 may lose 1 atom of oxygen, becoming HNO nitrous acid, under one equivalent of action, which provides H to from H2O water; but one atom of hydrogen is equally able to take up one of oxygen together with the hydrogen of the acid; thus HNO3 + H becomes H2O + NO2; or the same reaction taking place with the residue (nitrous acid) of the first case HNO3 + H becomes H2 O + NO. Zu each of these cases the work done electrically,

70

9.56

7:07

6-43 6-22 6.60

Cost unit
per

This shows an excess of cost of one-eighth by using salt, and this excess would increase according as the cost of nitric acid per lb. or per unit exceeded the figure given. Adding to the first figures enough to bring the cost up to practical working, or 1 atom of acid per unit 07990131 0930 as the cost per unit as compared with the other forms of battery. This is somewhat under that of Daniells, but that is capable of reduction by causing the copper to be deposited in useful forms, while this is at its lowest; the real drawback, however, to nitric acid batteries is the escape of nitrous gases, which are unwholesome and very injurious to all metallic substances; where these can be avoided, and the trouble attending its use is of little moment, the nitric acid cell is undoubtedly the most powerful and most advantageous source at present known from which to obtain a steady and powerful current.

(To be con 'inued.)

12:43

37 lb. at 7d.

7000

*0375

63-02

12.18

Nitric acid

1 atom 0393

61.98

11-93

30 per cent

0118

⚫0511

*0906

37.19

36-16

35-13

ON STAR-GROUPING, STAR-DRIFT, AND Le Sueur, with the great reflector erected at Mel

STAR-MIST.*

(Concluded from page 247.) URNING to the subject of star-mist, under propose to deal but with a small proportion of the evidence I have collected to prove that none of the nebula are external galaxies. That evidence has indeed become exceedingly voluminous.

I shall dwell, therefore, on three points only. First, as to the distribution of the nebula :They are not spread with any approach to uniformity over the heavens, but are gathered into streams and clusters. The one great law which characterises their distribution is an avoidance of the Milky Way and its neighbourhood. This peculiarity has strangely enough been regarded by astronomers as showing that there is no association between the nebula and the sidereal system. They have forgotton that marked contrast is as clear a sign of association as marked resemblance, and has always been so regarded by logicians.

Secondly, there are in the southern heavens two well-marked streams of nebule. Each of these streams is associated with an equally wellmarked stream of stars. Each intermixed stream directs its course towards a Magellanic Cloud, one towards the Nubecula Minor, the other towards the Nubecula Major. To these great clusters they flow, like rivers towards some mighty lake. And within these clusters, which are doubt less roughly spherical in form, there are found intermixed in wonderful profusion, stars, star clusters, and all the orders of nebula. Can these coincidences be regarded as accidental? And if not accidental, is not the lesson they clearly teach us this, that nebulae form but portions of the sidereal system, associating themselves with stars on terms of equality (if one may so speak), even if single stars be not more important objects in the scale of creation, than these nebulous masses, which have been so long regarded as equalling, if not outvying, the sidereal system itself in

extent ?

The third point to which I wish to invite attention is the way in which in many nebule stars of considerable relative brightness, and belonging obviously to the sidereal system, are so associated with nebulous masses as to leave no doubt whatever that these masses really cling around them. The association is in many instances far too marked to be regarded as the effect of accident. Amongst other instancest may be cited the nebula round the stars c and in Orion. In this object two remarkable nebulous nodules centrally surround two double stars. Admitting the association here to be real (and no other explana. tion can reasonably be admitted), we are led to interesting conclusions respecting the whole of that wonderful nebulous region which surrounds the sword of Orion. We are led to believe that

the other nebular in that region are really asso

ciated with the fixed stars there; that it is not a mere coincidence, for instance, that the middle star in the belt of Orion is involved in nebula, or that the lowest star of the sword is similarly circumstanced. It is a legitimate inference from the evidence that all the nebule in this region belong to one great nebulous group, which extends its branches to these stars. As a mighty hand this nebulous region seems to gather the stars here into close association, showing us in a way there is no misinterpreting, that these stars form one system.

The nebula round the strange variable star, Eta Argûs, is another remarkable instance of this sort. More than two years ago I ventured to make two predictions about this object. The first was a tolerably safe one. I expressed my belief that the nebula would be found to be gaseous. After Mr. Huggins' discovery that the great Orion nebula is gaseous, it was not difficult to see that the Argo nebula must also be so. At any rate, this has been established by Captain Herschel's spectroscopic researches. The other prediction was more venturesome. Sir John Herschel, whose opinion on such points one would always prefer to share, had expressed his belief that the nebula lies far out in space beyond the stars seen in the same field of view. I ventured to express the opinion that those stars are involved in the nebula. Lately there came news from Australia that Mr.

The substance of a Lecture delivered by R. A. PROCTOR, B.A., at the Royal Institution on May 6.

Eight pictures of nebula were exhibited in illustration of this peculiarity.

families of satellites; we see the rings of Saturn, bourne, has found that the nebula has changed in which minute satellites must be as the sands largely in shape since Sir John Herschel observed on the sea-shore for multitude; the wonderful it. Mr. Le Sueur accordingly expressed his belief zone of asteroids; myriads on myriads of comets; that the nebula lies nearer to us than the fixed millions on millions of meteor systems, gathering seen in suure fold of view. more more richly man,

lately, however, he has found that the star Eta
Argus is shining with the light of burning hydro-
gen, and he expresses his belief that the star has
consumed the nebulous matter near it. Without
agreeing with this view, I recognise in it a proof
that Mr. Le Sueur now considers the nebula to
be really associated with the stars around it. My
belief is that as the star recovers its brilliancy,
observation will show that the nebula in its
immediate neighbourhood becomes brighter (not
fainter through being consumed as fuel). Infact,
I am disposed to regard the variations of the
nebula as systematic, and due to orbital motions
among its various portions around neighbouring

stars.

As indicative of other laws of association bear
ing on the relations I have been dealing with, I
may mention the circumstance that red stars and
variable stars affect the neighbourhood of the
Milky Way or of well-marked star-streams. The
constellation Orion is singularly rich in objects
of this class. It is here that the strange "vari-
able" Betelgeux lies. At present this star shows
no sign of variation, but a few years ago it exhi-
bited remarkable changes. One is invited to
believe that the star may have been carried by its
proper motion into regions where there is a more
uniform distribution of the material whence this
orb recruits its fires. It may be that in the con-
sideration of such causes of variation affecting our
sun in long past ages a more satisfactory explana-
tion than any yet obtained may be found of the
problem geologists find so perplexing the former
existence of a tropical climate in places within
the temperate zone,
or even near the Arctic
regions.*

his neighbourhood they form the crown of glory which bursts into view when he is totally eclipsed. But wonderful as is the variety seen within the planetary system, the variety within the sidereal system is infinitely more,amazing. Besides the single suns, there are groups and systems and streams of primary suns; there are whole galaxies of minor orbs; there are clustering stellar aggregations, showing every variety of richness, of figure, and of distribution; there are all the various forms of nebula, resolvable and irresolvable, circular, elliptical, and spiral; and lastly, there are irregular masses of luminous gas, clinging in fantastic convolutions around stars and star-systems. Nor is it unsafe to assert that other forms and varieties of structure will

yet be discovered, or that hundreds more exist which we may never hope to recognise.

But lastly, even more wonderful than the infinite variety of the sidereal system, is its amazing vitality. Instead of millions of inert masses, we see the whole heavens instinct with energy, astir with busy life. The great masses of luminous vapour, though occupying countless. millions of cubic miles of space, are moved by unknown forces like clouds before the summer breeze; star-mist is condensing into clusters; star-clusters are forming into suns; streams and clusters of minor orbs are swayed by unknown attractive energies; and primary suns singly or in systems are pursuing their stately path through space, rejoicing as giants to run their course, extending on all sides the mighty arm of their attraction, gathering from ever new regions of space supplies of motive energy, to be transformed into the various forms of force,-light, and heat, and electricity, and distributed in lavish abundance to the worlds which circle round

them.

-

It remains that I should exhibit the general results to which I have been led. It has seemed to many that my views tend largely to diminish our estimate of the extent of the sidereal system. we regard its vast extent, or its infinite variety, Truly may I say, in conclusion, that whether The exact reverse is the case. According to accepted views there lie within the range of our portion, the sidereal system is of all the subjects or the amazing vitality which pervades its every most powerful telescopes, millions of millions of man can study, the most imposing and the most suns. According to mine, the primary suns within stupendons. It is as a book full of mighty problems, the range of our telescopes must be counted by of problems which are as yet almost untouched tens of thousands, or by hundreds of thousands by man, of problems which it might seem hopeat the outside. What does this diminution of less for him to attempt to solve. But those probnumbers imply but that the space separating sun lems are given to him for solution, and he will from sun is enormously greater than accepted solve them, whenever he dares attempt to decitheories would permit? And this increase im- pher aright the records of that wondrous volume. plies an enormous increase in the estimate we are to form of the vital energies of individual suns. For the vitality of a sun, if one may be permitted the expression, is measured not merely by the BY THE REV. E. KERNAN, CLONGOWES COLLEGE. amount of matter over which it exercises control, but by the extent of space within which that matter is distributed. Take an orb a thousand

times vaster than our sun, and spread over its

surface an amount of matter exceeding a thon-
sandfold the combined mass of all the planets of
the solar system:-So far as living force is con-
cerned, the result is-nil. But distribute that
matter throughout a vast space all round the orb
that orb becomes at once fit to be the centre
of a host of dependent worlds. Again, according
to accepted theories, when the astronomer has
succeeded in resolving the milky light of a portion
of the galaxy into stars, he has in that direction,
at any rate, reached the limits of the sidereal
system. According to my views, what he has
really done has been but to analyse a definite
aggregation of stars-a mere corner of the great
system. Yet once more. According to accepted
views, thousands and thousands of galaxies,
external to the sidereal system, can be seen with
powerful telescopes. If I am right, the external
star-systems lie far beyond the reach of the most
powerful telescope man has yet been able to con-
struct, insomuch that perchance the nearest of
the outlying galaxies may lie a million times
beyond the range even of the mighty mirror of
the great Rosse telescope.

But this is little. Wonderful as is the extent
of the sidereal system as thus viewed, even more
wonderful is its infinite variety. We know how
largely modern discoveries have increased our
estimate of the complexity of the planetary sys-
tem. Where the ancients recognised but a few
planets, we now see, besides the planets, the

Sir John Herschel long since pointed to the variation of our sun as a possible cause of such changes of terres

trial climate.

SCIENCE FOR THE YOUNG.*

(Continued from page 223.)

§ II.-FLEXIBILITY. Lthout any permanent separation of the parALEXIBILITY is the capability of bending

ticles in a body. This is an important property, in consequence of practical questions which it involves.

No. I.-Laws.-A body in which the dimension of length is considerably greater than the other two dimensions, may be viewed as constituted by three sets of particles-the upper, the lower, and the middle. The conditions of these in a flexed body are the subject of the few but important laws of flexibility. A rod with wires passed through it, shows well, in an enlarged form, the meaning of the laws. When the wires carry white beads the action is made still more evident, Fig. 37. Lead or some body that keeps the bent form, is the best material for the rod.

Law I. The upper particles of a flexed body are separated without destroying their molecular attraction. Hold the wired rod, the wires perpendicular, bend the ends down, the wires diverge, forming an angle between each pair. The beads, as Fig. 38, represent the particles as separated by the action of bending.

N.B.-The terms upper and under, are not to be taken in their ordinary sense only. For then the laws would refer to but one sort of flexioncentre raised up, ends bent down. Every flexed

body has a convex and concave side. And in this sense are used the terms upper and under.

compressed. Look at the beads below (a), they Law II. The lower particles of a flexed body are are close up, or perhaps overlapped.

*The copyright of this series of articles is reserved by the Author.