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-SCREW PROFELLER.-Could one of your readers tell me how to obtain the pitch of a screw er ?-R. W.

-BICHROMATE BATTERY.-Will "Sigma other brother correspondent kindly tell me what -roper distance to leave between the plates of a nate battery? The plates are 5in. by 2in. Also the best way to fasten the copper wire to the plate ?-THOMAS J. O'CONNOR.

J-HOROLOGICAL.-Would some horological ber kindly inform me by what rule watchmakers et watches-viz., what is the difference between 1m. 5-10th and one 1m. 9-10th ? Have they the number of teeth and leaves to wheels and 4? Also, how many sizes of watches do the trade ize?-B. E. LODDY.

-BLEACHING IVORY.-Can any subscriber inform me how the handles of table cutlery that ecome yellow with use, may be restored to their : whiteness ?-BLACK RAVEN.

23-WATER-WORKS.-Can you or any of your pondents inform me the cost of laying mains in sand roads per mile? In supplying water by graviwhat head is required to overcome the pressure PT pipes ?-T. W. C. 7.]-TO "INDUCTORIUM."- Will "Inductostate the size of secondary wire he uses? and as I allows in. between the discs, must it be wound vards and forwards in this space until filled, and the next, and so on ?-T. W. C.

08.)-SPECTROSCOPE.-Can any of your correlents give me instructions and drawings for making ctroscope ?-T. W. C.

1 99.]-SCIENCE AND ART EXAMINATIONS.I ask Mr. G. E. Davis what books he would recomWard to one preparing for the Organic Honours Paper, ext May's examinations ?-CROW TREES.

700.]-COPIES OF COINS IN ELECTROTYPE. ill some kind brother please tell me how to take es of coins, &c., in electrotype ?-WILLIAM S.

TCHER.

1701.]-CLEANING COINS.-Will you or one of your ay readers please to inform me how to clean old as (silver and copper) without injuring the coins?LLIAM S. FLETCHER. 4702.]-TRUE HEART FOR TRAVERSING.-I dewould be grateful if any one would inform me, by a all sketch or otherwise, how to describe a true heart traversing purposes, from lin. to 3in.-GOOD

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4709.]-CHANGE WHEELS.-My thanks to "B. H." his answer to query 4371, p. 454, but he evidently stakes what I want. He gives me an answer to ange from oue hank to another. I want to know how ey find the proper wheels in the first instance. I ve never seen a rule myself, and don't know whether ere is one or not. If "B. H." could assist me any rther I should be obliged.-GOOD WORDS. 4704.]-CHANGING SURNAME.-I wish to change surname. How can I do it ?-M. SPIEGELHALTER. 4705.]-NATURALIZATION.-What steps must I e to become a naturalized Englishman?-M. SPIEGEL, 4706.]-PHOTOGRAPHY.-I put the water that I 3h the silver prints in into a deep mug and precipitate silver with common salt, and have done so with the atest success for two years. The silver precipitated utifully, but now it is just the reverse, it won't peritato at all, and I have put lots of salt in, but to no il. Would some kind reader of the MECHANIC be good ugh to tell me the reason, and if there is a cure, what t?-IN A FIX.

4707.)-STEAM.-Can any of our numerous readers me what would be the number of cubic feet of steam minute, issuing from a pipe 2 in. diameter, under a ssure of 40lb, per square inch? Would they also give rule and working of the same, as I have no books ating on the subject? And also say where I could a work on the subject ?-E. J. JACKSON.

wash-house copper (on the ground floor) to a bath (on the first-floor), without carrying it? Will a pump answer the purpose? If so, what sort? I have an idea that hot liquids cannot be pumped, as they would injure the pumps; is this idea correct, and if so what other expedient can I adopt? If, however, hot water can be pumped, I presume that the same pump will also serve to pump up cold water from the butt? 2nd. Would india-rubber or gutta-percha tubing answer? Any information on these points would oblige ?-A HANDY MAN. [4715.]-SILK DRESSING MACHINE.-Having seen a letter in the MECHANIC for June 10th signed E. Davis, I should be much obliged if he would, through the MECHANIC, furnish me with the particulars regarding a silk dressing machine he mentions, on which he can change the sheets of silk in a few minutes.-A. T. T. [4716.]-FINISHING BLACK CLOTH.-Can any of your subscribers inform me of the best method of putting a bright face or finish upon black cloth ?-J. R.

[4717.]-BINDING MAGNETIC WIRE.-I believe it is essential that the winding of the wire for magnetic purposes should be performed as evenly as possible. Like a reel of cotton, I find it difficult, or, indeed, impossible, to accomplish it merely with the hand, as it is produced by the regular manufacturer. Would some one kindly inform me what means to adopt to effect my object ?-MAGNET.

[4718.]-VARNISH FOR BRIGHT STEEL WORK. Can you inform me of any preparation for covering bright steel work, so as to prevent its rusting, and at the same time preserve its bright appearance; something that will have the same effect as varnish on paint, enabling me to wash the work when done?-THOS. PRIOR.

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[4721.]-FOSSILS.-Will whether I can obtain many fossils in the neighbourhood of Hunstanton and along the coast to Cromer? What are they; and where ought I to look ?-H. U. [4722.]-CONSTRUCTION OF SHIPS.-I should be obliged if any correspondent will tell me what is ScottRussell's "wave-line principle" for the construction of vessels.-N. A.

[4723.]-WATER BAROMETER.-Will "Cornubia " (p. 396), kindly answer me the following questions:1st, What a thermometer has to do with graduating the degrees on his barometer? 2nd. If the heat would not have any effect in expanding the air contained in the glass bulb, and so effect the height of the column of liquid in the glass tube? 3rd. Why not graduate the degrees on the tube at once, instead of having the revolving apparatus?-GEOMETROS.

[4724.]-CONSUMPTION OF COALS.-Some time ago there was a commission appointed to inquire into the consumption of coal. Can some one inform me if that commission has yet published its report? And if it has, where, and at what price it may be obtained? Or what amount of coal is consumed in the United Kingdom, locomotive, and marine ?-PETRUCHIO. in the working of steam engines of all classes, stationary,

UNNOTICED QUERIES.

IN future, if any query remains unanswered for four weeks, we shall insert the number and subject of the query in this list, where it will remain for two weeks, if not previously replied to. We trust our readers will look over the list, and send what information they can for the benefit of their fellow-contributors.

Since our last J. H. Rumsey has answered 4112; John Terras, 4159: "Oxoniensis," 4200, 4270; "A. S. C.," 4224; "S... r,” 4242; “ M.R.C.S.," 4274, 4275.

4708.]-LOSS OF VOICE.-For the last two or three irs my voice has been very husky and indistinct, and have generally to give a short cough before I can sak a word. I shall be very glad if some kind reader l tell me what will improve it.-A FORESTER. 4709.]-TO MR. PROCTOR.-Will Mr. Proctor kindly nish me with the dimensions of the stand figured in 4261 "Half-hour with the Telescope," p. 17, and say 4265 ether he thinks it would be suitable for an instru- 4266 atent 4in. aperture 5ft. long? I wish to make a stand 4269 tich shall give a steady motion, and be easily moved 4284 forth in place to place. Perhaps Mr. Proctor's experience 4286 all by enable him to suggest some simpler plan that would moderately efficacious.-TURTON.

aver.

Cotton Spinning, p 406.
Fixing and Colouring Prints on Glass, 406.
Water Gilding, 406.
Associate of Art Degree, 406.
Alabaster Glass. To Mr. J. Leicester, 406.
Alloys for Tin Foil, 406.

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Cotton Spinning, 406.

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[4710.]-FASTENING BRASS TAPS IN KITCHEN ILER.-Can any of your numerous readers inform how to tighten a brass tap to kitchen boiler that has come loose ?--INQUIRER.

Force Pump for Irrigation, 406.

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[4711.]-COLZA OIL.-Will any brother reader be 4302 reas ad enough to instruct me how to test the quality of 4303 Cast-Iron, 407.

ow, the za oil.-M. Q. W.

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(4712.]-AIR v. STEAM.-I want to substitute air 4311 steam (like many others I suppose) but there is 4312 supposed impossibility to contend with-namely, 4315

Model Mills, p. 430.
Destructive Soap Powders, 430.
Emigration, 430.
Rocking Chair, 430.
Cleveland Ironstone, 430.

burde boiler as it does to move
do that it requires just as much power to force the air into 4317 Sizing, 430.

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s difficulty could be overcome, could any correspon- 4327

the engine. Now if 4326 Polariscope for Lantern, 430. Want of Pressure, 430.

at tell me, if air even then could cope with steami?-4331 Stone for Trinkets, 431.

ICUS.

I of the

[4713.1-BEES.-I wish to remove my hive inside a ilding during the winter. Can any reader inform me he bees would pass in and out through a small hole de in a 9in. brick wall, and how bees are fed, or what hould feed them with in the winter? I think a few iters on bees, through the MECHANIC Would be found Try acceptable to many of its readers.—J. G.

4332

4333

Black Glass of Antimony, 430. Lancashire Black, 480.

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4714.]-HOT OR COLD BATH.-Can any reader give information on the following points? 1st. What ans could I adopt in order to get hot water from a

Draught Furnace for Smelting Lead Ore. 4339 La Crosse, 430.

4349 Heating House with Hot Air, 481. 4350 Barometer, &c., 431. 4351 431.

4352

Case for Ferns, Weaving, 431,

DOMESTIC RECIPES.

From the Food Journal.

VEGETABLE SOUP.-Place one onion, cut in pieces, in a saucepan, with 3oz. of butter, and brown it; then add finely-shredded turnips, parsnips, leeks, carrots (also a white carrot, if procurable), green celery, a little sorrel, one small potato, and a few French beans and green peas, all of which are to be tossed and browned in the butter, with sufficient quantities of salt and pepper. Pour in a little water or stock, crush the vegetables slightly, then fill up with more water, and let the soup simmer for two hours. A little rice or pearl barley can, with advantage, be added to the vegetable. Care must be taken not to get the soup of too thick a consistency.

TO KEEP MUSHROOMS WITHOUT PICKLE.-Let the mushrooms be peeled, and the insides taken out; then lay them to soak in water for two or three hours, after which they must be dried. Lay them on tin plates, and set them up in a cool oven, an operation which must be repeated several times, until they are thoroughly dry. They must then be put in pots, and kept from damp.

TO MAKE KETCHUP.-To a peck of mushrooms, put two handfuls of salt. Let them stand two days; then strain them out, and boil for half or quarter of an hour. Scum them well, and season as you like with ginger, pepper, cloves, and garlic, all of which must be boiled but the garlic; let them stand for a day or two, and then put into bottles with sweet oil, tying over some perforated paper.

A COUNTRY CAPTAIN.-Cut a fowl to pieces as for a fricaseé; salt, pepper, and cayenne pepper it to taste, The fowl must be fried in butter by itself; three or four large onions fried brown in butter are to be sent up with it, with fried crumbs of bread, lemon peel, and gravy as for a roast fowl.-From an old MS.

A TURKISH BROIL.-Cut from a small cod-fish as many slices as are required, rub them with a little salt, oil, lay the fish over, set it on a moderate charcoal fire, and dip them in flour; then rub a gridiron with olive and turn the fish often. When nicely browned on both sides, take it off, then cover the surface of a dish with some finely chopped parsley and onions, place the fish over, with one or two lemons cut in quarters round the dish, and serve hot.

USEFUL AND SCIENTIFIC NOTES.

RUSTIC PICTURE FRAMES.-Rustic wood for this and other purposes is in great favour nowadays. According to the Scientific American, with a little care in selection of material and skill in handling tools, we may frame our engravings and paintings at slight cost. Oak wood, denuded of the bark, presents a beautifully corrugated surface, out of which the knife easily removes the few fibres which adhere, and it is ready for varnishing as soon as it is seasoned. The "season cracks," should they occur, may be filled with dark brown putty, and will even heighten the general effect. Take a thin board of the right size and shape, for the foundation or "mat; "saw out the inner oval or rectangular form to suit the picture. Nail on the edge a rustic frame made of the branches of hard, seasoned wood, and garnish the corners with some pretty device, such, for instance, as a cluster of acorns. Ivy may be trained to grow around these frames with beautiful effect.

PLATING COPPER AND BRASS WITH ZINC.

According to Büttger, copper and brass can be easily coated with zinc by immersing them in a boiling bath of sal ammoniac containing zinc foil or powder. The deposit of zinc made in this way is brilliant, and adheres firmly to the copper and brass. Whether iron could be coated or galvanized in the same way is not stated by the author, though the use of sal ammoniac in the ordí nary process is well understood. He first prepares finely-divided zinc, by pouring the molten metal in a previously strongly-heated iron mortar, and stirring until nearly cold. The pulverulent zine thus obtained is placed in a porcelain vessel, and to it is added a concentrated aqueous solution of sal-ammoniac. This mix. ture is heated to boiling; and the copper or brass objects to be coated with zinc (but previously wellcleansed, and, best, even with an acid) are then placed in the liquid, wherein they become coated with a brilliantly-white adhering layer of zinc.,

METHOD OF PURIFYING ILLUMINATING GAS. E. Pelouze modifies the Lamming mass now generally employed for the purpose of purifying illuminating gas, by adding sulphuric acid. He sprinkles the purifiers containing oxide of iron and sawdust, with water, to which 20 per cent. of sulphuric acid, of specific gravity 1.53 (53 Baumé), has been added, and after the mass has dried up sufficiently, passes the gas through. After use it is necessary to restore the sulphuric acid, and to remove the sulphate of ammonia that may have been formed. It is said that napthalin is not removed from the gas by this method. A mixture of oxide of iron and sawdust thus prepared would serve an excellent purpose as a disinfecting agent to be added to the earth in the earth-closet, in stables, cesspools, and the like, but where it has to come in contact with metals care must be taken not to have free sulphuric acid present. Ordinary copperas or sulphate of iron and sawdust, with native hematite, or bog-iron ore, would also make a valuable disinfecting mixture, and would be nearly as cheap as any of the others.

NEGLECT OF MUSHROOMS.-How is it that mushrooms should be used so timidly, and left to rot by thousands in field and forest, when, with a rise in the price of flour, or of meat, they might and ought to give dinners for numberless cottagers, whose children could gather these "vegetable beef-steaks" with ease and with profit? Is there not the common mushroom, and the fairy-ring mushroom or Scotch bonnet, the blewitt and the orange-milk mushroom, the morel-and might there

not be the truffle, had we less pride in borrowing from our neighbours, and more ingenuity in utilizing the loan? How is it that France is ahead of us in prizing these fungi as delicacies, and Italy very far ahead, so that £4000 worth yearly are sold in the market-place of Rome? We, says the Food Journal, pride ourselves on our roast beef; let us not have to blush for the scantiness and dearness of our vegetable accompaniments. M. Roques has called mushrooms, "the manna of the poor," and yet in England the poor do not consider themselves divinely chosen enough to gather this

manna.

CARDED OAKUM AS A SURGICAL DRESSING.So many advantages are possessed by carded oakum as a surgical dressing that we (Lancet) expect it to be largely employed in the military hospitals of France and Germany during the present war. As, however, its qualities are not yet so widely known as they should be, it may be useful at the present juncture to refer to them. The material is simply old rope shredded in prisons and workhouses, and carded by machinery. It is of a bright brown colour, with the well-known tarry fragrance. A little of the oakum is roughly drawn into a suitable shape for covering the wound, then wetted, and applied to it. All discharge is absorbed by the dressing, and any bad odour is effectually destroyed. By dipping it into hot water, and covering it with oil silk, a convenient antiseptic poultice is formed, easily made, very light, and answering perfectly its purpose. It thus supersedes the use of lint, ointments, and linseed-meal or bread poultices. It is easily burnt-no small advan

tage in a crowded hospital, where bad-smelling applications are a fertile source of decrease if not quickly destroyed. Its simplicity of application saves much time and labour-a great consideration where the nursing staff is overtaxed, as must always happen after serious engagements. Its cheapness is another great advan tage. Carded oakum can be procured, we believe, for something like ninepence a pound, about a fifth or a sixth of the cost of lint.

NEW ELECTRIC MACHINE.-Among the improvements of the "Influence or Electropher machine," invented by Herr Holtz, of Berlin, a new construction, by Professor Poggendorff, is especially noteworthy, This machine, we learn from the Monatsbericht of the Berlin Academy, has two rotating glass plates; and the conductors are placed in a convenient manner, especially adapted for demonstrations in lecture-rooms. It exceeds in efficiency all machines hitherto made, and is manufactured by Borchhardt, of Berlin. For the purpose of cleaning the glass plates, Professor Poggendorff recommends rubbing with petroleum.

ALLOY FOR TAM-TAMS, OR GONGS, AND CYMBOLS. From the Chemical News we have an account

answers better, and can be rolled out. The process is similar to that in use in China, and is carried out at

Paris by M. Cailar.

POISON PLANTS.-Mr. Worthington Smith records in the Journal of Botany an instance of a fatal case of poisoning by eating the root of the water-dropwort, Enanthe crocata, an umbelliferous plant, cominon in ditches and wet places. A carter at Staplehurst, in Kent, ate some of the roots whilst at work, supposing them to be the wild parsnip. In about an hour he became unconscious and convulsed, and death occurred in another half-hour, before medical aid could be obtained. The man had fed his horse with roots of the same plant, and the animal also expired about two hours after eating them. There is no doubt that the Enanthe is a virulent poison, but it seems strange that the horse as well as the man should not have rejected a plant of so acrid and suspicious a flavour. Several wild Um belliferæ are amongst the most dangerous of British plants.

fectly true: but the fact is, that no simple substance
given alone will support life. The most nutritive
materials, such as albumen, fibrin, gluten-to say
nothing of such substances as starch or sugar-all equally
fail to support life when given alone.

The Sixpenny Sale Column is the only place in -_
appear queries sent by J. E., Li
S. R.

W. J.-We cannot give the addresses of corum,
If you wish for the address of the gentlene
you had better ask for it through TM
Column.

AN ASSOCIATE OF R. S. MIXES.-We
take to receive the specimens. D

A

SCAVENGER BEETLES.-Scavenger beetles are to
be seen wherever the presence of putrescout and offen-
sive matter affords opportunity for the display of their
repulsive but most curious instincts; fastening on it
their strength, and rolling it along in search of some J.
with eagerness, severing it into lumps proportionate to
place sufficiently soft in which to bury it, after having
deposited their eggs in the centre. I had frequent
opportunities, especially in traversing the sandy jungles
in the level plains to the north of the island, of observ
ing the unfailing appearance of these creatures in-
stantly on the dropping of horse-dung, or any other sub-
stance suitable for their purpose; although not one was
visible but a moment before. Their approach on the
wing is announced by a loud and joyous booming sound,
as they dash in rapid circles in search of the desired
object, led by their sense of smell, and evidently little
assisted by the eye in shaping their course towards it.
In these excursions they exhibit a strength of wing and
sustained power of flight, such as is possessed by no
other class of beetles with which I am acquainted, but
which is obviously indispensable for the due performance
of the useful functions they discharge.-Sir J. E.
Tennent's Natural History of Ceylon.

HARMLESS SALAD HERBS.-It is a pity people,
says the Pall Mall Gazette, in this country neglect to
herbs which are now altogether wasted. Watercress is
add to their diet by a more liberal use of harmless salad
It has lately been pointed out that our sorrel plant is a
very well in its way, but is not everywhere accessible.
more delicate and agreeable variety than the wood
sorrel so largely used at table in France and Germany;
that the common shepherd's purse and lady's smock
may supply the place of the watercress; that the
famous "barbe des capucins" of the Paris restaurants
is nothing more than the blanched shoots of the wild
chicory, and that the "salade de chanoine" is our own
neglected corn-salad. Our peasants, however, have yet
to learn the art of making salad, and the wisdom which
selects and dulcifies with oil the bitter qualities of such
herbs as the endive or its proposed humbler substitutes,
the avens, the bladder campion, and the tender shoots
of the wild hop. This art must descend to them from a
more cultivated class, and in nothing is the English
middle-class table more generally deficient than in the
wholesome, varied, and savoury salad which adds an
attraction to the simplest fare, and gives something of
freshness, if not of refinement, to the richest as to the
poorest table.

much labour.

GILLAIRD.-The ENGLISH MECHA for the purpose of advertising grea a "remuneration for their idea

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we seldom receive letters like you BRITISH WORK MAN. We direction indicated. There will ar ones on the look out for flats. In the weaker party should be doubly A BLACKSMITH.-The following a you ask for :-A Millimetre = 01; ; Cent metre 0-3937049in.; a Decimetr Metre 39-370432in., or 3-28089ft, 302 a Kilometre = 1095-6231 yards; = 6-21377 miles.

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A. ALLEN. We do not think it would g
pearance of our journal to insert paris
among the matter. They are to alar
poses advertisements, and should s
with the volume.

HESPERUS-If your claim has been all-wri
probably share in the settlement which de
-5s. in the pound, we believe.

D. F. A.-We cannot give the information we
ment Column was designed to meet cases in
H. B.-Fecula is a term sometimes applia 2,
sometimes to cornflour. The most ordinary
is a pulverulent ma ter obtained by breaks E
texture of plants, washing with water, sni kak
the deposit.

EMERY.-B. J. (Birmingham-No. Enery is
granular, or compact variety of a mineral, EA
corundum. It takes its name from Cape Em -
island of Naxos, where it is found in sbandasıca
whence it is largely imported.

B. G. K.-The weight of a fort of round bar imm diameter would be 51b. 1370z.; of lția square bar. 7lb. 7.5oz.

BRITANNIA METAL.-F. C. W.-Britania metal is om posed of equal parts, brass, tin, antimony, and las muth.

JOHN HAMPDEN (Wilts).-We cannot insert advertisements on condition of any one screpting your challenge and overturning year theories. CRYPTOGRAPHER.-Next week

J. B.-"Accessories to the Microscope" next week.

reply on melting cast steel.

serted.

ometers is an advertisement, and therefore 2A SCREW POWER, BY J. K. P.-Next week. LEX.-You find fault with the style of writing of correspondents, and fall into similar errors yo You accuse "R. P.," in his letter on Art charges, of "deliberate equivocation," and c by saying that his letterproves nothing to own ignorance." Your reply to Scriptore=2 same style. One way to improve others is example ourselves.

SEA CUCUMBERS. - The holothuriæ, or sea-cuof the method now followed by Messrs. Riche and cumbers, may be regarded in one light as soft seaChampion, for making the sound-producing instruments urchins, and in another as approximating to the annealluded to, which consist of an alloy of 80 parts of lides or worms. Their suckers are similar to those of copper and 20 of tin, which is hammered out with fre- the true star-fishes and sea-urchins. Besides progression quent annealing. Au alloy of 78 of copper and 22 of tin by means of these organs, they move, like annelides, by J. O. BRINE writes to thank Mr. Geo. Jacken Air As the extension and contraction of their bodies. The mouth is surrounded by plumose tentacula, the number AN ENQUIRER.-Your query about price, dn, da of which, when they are complete, is always a multiple of five. They all have the power of changing their shapes in the strangest manner, sometimes elongating themselves like worms, sometimes contracting the middle of their bodies, so as to give themselves the shape of an hour-glass, and then again blowing themselves up with water, so as to be perfectly globular. The great sea-cucumber is the largest of all the known European species, and probably one of the largest Cucumeria in the world, measuring, when at rest, fully one foot, and capable of extending itself to the length of three. Under the influence of terror, it dismembers itself in the strangest manner. Having no arms or legs to throw off, like its relations the luidia and the brittle star, it simply disgorges its viscera, and manages to live without a stomach; no doubt a much greater feat than if it contrived to live without a head. According to the late Sir James Dalyell, the lost parts are capable of regeneration, even if the process of disgorgement went so far as to leave but an empty sac behind. Considering the facility with which the sea-cucumber separates itself from its digestive organs, it is the more to be wondered how it tolerates the presence of a very remarkable parasite, a fish belonging to the genus Fierasfer and about 6in. long. This most impudent and intrusive comrade enters the mouth of the cucumber, and, as the stomach is too small for his reception, tears its sides, quartering himself without ceremony between the viscera and the outer skin. The reason for choosing this strange abode is yet an enigma.-Dr. Hartwig's "Sea and its Living Wonders."

THE NEW ACT ON FACTORIES AND WORKSHOPS.-The statute to amend and extend the Acts relating to factories and workshops was passed on the 9th August, in reference to print-works and bleaching and dyeing works, as also to amend the Acts on factories and workshops. There are two parts in the statue and three schedules. The first part relates to print-works and bleaching and dyeing works, and is to be construed as one with the Factory Act Extension Act, 1867; and after January 1st, 1872, the principal Act is to apply to print-works and bleaching and dyeing works. Certain regulations are to be enforced on the 1st of January, 1871, in Turkey-red dyeing works. The second part of the statute relates to fruit and fish preserves. The schedule to the Factory Acts Extension Act, 1867, and the schedule in the Workshop Regulation Act, 1867, are to be construed as if they were contained in each of those schedules. In the schedules the permanent modifications are set forth. In the manufacture of preserves from fruit, and in the processes of preserving or curing fish, women may be employed, between the 1st of June and the 14th of December, for a period not exceeding 14 hours on any one day.

ARTIFICIAL BUTTER.-Apparently astonishing as the idea is, the manufacture of artificial butter (beurre artificiel) is seriously contemplated in France. Α Parisian contemporary states that M. Meye, of Paris, has taken out a patent for the manufacture of artificial butter, which according to the journal in question, is to be used as a substitute for that ordinarily exported to England and Russia. The description of the process is, that animal fat is subjected to great pressure, by which the stea: ine is extracted for making candles, or bougies: an oily material being at the same time obtained, the composition of which is identical with that of butter. The question then arises, how is the taste of this "composition" to be rendered similar to that of butter? M. Meye is quite equal to the occasion; he says that he subjects the animal oil to a succession of scientific processes and manipulations, the nature of which he explains at great length and with marvellous ingenuity. He traces the relations of unsophisticated grease to sophisticated fat, and crowns the edifice in rare style, by showing the precise identity of each with what he calls butter," and indulges in the most sanguine anticipations about the success of his "invention."

GELATIN.-It is said that an animal fed on gelatin dies rapidly of starvation and inanition. This is per

ANSWERS TO CORRESPONDENTS.

All communications should be addressed to the EDITOR of the ENGLISH MECHANIC, 31, Tavistockstreet, Covent Garden, W.C.

The following are the initials, &c., of letters to hand up
to Tuesday morning, August 23, and unacknowledged,
elsewhere:-

EDWIN TRAYLER, R. A. Proctor, J. B., T. S. H., E. O. T.,
J. B. F., J. P. H., J. H., R. F., R. W. H., Revd. E. Ker-
nan, Scapegrace, Tom H., J. R. T., Ernest Hart, J.
Willing, Unprejudiced, W. Perryman, Wm. Black,
J. A. Mays, J. B. H., R. I. A., Albert Inchcliffe, St. John
T. Gore, Knorferd, Geo. H. Hawley, J. M. Thomas,
A. Stringer, H. Pocklington, W. R. Bole, J. Gale, E. B.
Fennessey, H. E. Hutchings, H. T. Roche, Trinitro-
phenic Ferrum, E. W. A., P. S. J., J. Scarr, San
Sebastian, Carlos, Geo. Evans, S. Priestley, E. M.
Robinson, Velocipede, J. Bourne and Co., H. W.
Reveley, M. A. C., J. Lander, J. P. H., A. J. Jarinan,
Jos. Mosley, J. D., J. Lee, Paddy, J. Bowley, Compen-
sited Balance, J. Keen, H. T. Pocklington, Sable,
A. L. C., W. E. D., Chas. Lucas, E. H. Ludgate, J. P. S.,
J. G., J. C. L., R. W. D., New Subscriber, R. D., G. H.,
E. Daw, Sergius, Unit, C. B., H. T. A., R. Chapman,
Checkache, Carter, Draper, B. Walton, G. H. G.,
Urban, W. W., Endeavour, J. H. T., James H. Smith,
Hopeful.

G. E. DAVIS.-MS. of Inorganic Chemistry
E. L. G.'s letter and replies next week.
Jos. MILLINGTON.-We expressed your ides.
J. M.-We don't answer queries by post.
BERNARDIN.-Your suggestion for a passpor
for the Continent, but of no service
mechanics.

ACHROMATIC.-Your proffered articles on the
scope" would be acceptable, provided you di“:
over ground covered by others.
H. W. T.-Your query has no practical value.
USEFUL.-See answer to "H. W. T."
FILTERS.-W. E. Ivey will find fall informati-
subject in Vol. X., pp. 112, 152, 578, 611.
A. W. PRIEST.-Purchase the volumes of the
MECHANIC containing "The Lathe and its Cas
SECONDS PRACTICAL WATCHMAKER.-Next
J. O'CONNEL.-We know no reason to alter
expressed on your pictures.

J. BASKERVILLE on "Link Motion," next

THE PHANTOM WHEEL.-We have rece of letters on this question in answer to the big Blacksmith," all testifying to the in of his

from the letters.

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statement on the want of rigidity a We never before witnessed such CASTERCE O opinion. We have not room even cre estrec A. G. V. GOODEUR.-Send us the best you ORGAN BUILDING.-"R. W. D." and others "Adept." The last we heard of our esteemed as spondent was that he was unwell, but that be soon to be able to continue his papers. N heard, we fear he is not recovered. It o that Mr. Kimble, another able correspa organ building, wrote us about ten weeks sinc was obliged to go to another climate for the be his health.

W. W. HARRIS.-See footnote to Hermann
article on " Harmonium," No. 268, p. 178.
ROBERT R.-See series of articles on "Paintin
Decoration" now appearing in the Building New
J. M.-Isocheimal means "equal winters;"' 1.6., b
the same mean winter temperature. It is fro
Greek-isos, equal; cheima, winter.

R. E. Y.-"Beuheyl" is a mining term and sign
living stream. It is applied by tin miners to ap
tion of a rock which is impregnated with tin.
S. R. B.-The pancreas is a fleshy gland situated
and behind the stomach, secreting a saliva-like
which assists digestion. The literal meaning of
word is "all flesh."

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STRACT OF A PAPER BY DR. ZÖLLNER,
ON THE TEMPERATURE AND PHYSICAL
CONDITION OF THE SUN.*

BY RICHARD A. PROCTOR, B.A., F.R.A.S.
Author of "Other Worlds than Ours," &c.

a

Assume further that

=

=

the mean height of the barometer in metres. density of the gas, at the temperature of melting ice, and at the pressure corresponding to the barometric height a, at the earth's surface.

density of the gas in the inner space mentioned above, under pressure p; and at the absolute temperature ti.

= the coefficient of expansion of the gas for 1° Centigrade. From the law of Mariotte and Gay-Lussac we have the following relation :

σ =

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The pressure pa may be considered as equivalent to the pressure of the outer solar atmosphere at its base. Next let

ha certain height above the base. the pressure at this height.

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t

PAPER of considerable scientific interest has recently been contributed by Dr. öllner to the subject of the "Sun's Physical :ondition." The following paragraphs may be garded as an abstract (and, in some places, a anslation) of this paper, which would be too ong to appear in full in these columns. It has eemed best to give the calculations in full, ecause, though too complex to be understood by all our readers, they will be acceptable to many. P. The results to which they lead can hardly fail to be generally interesting.

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The solar prominences may be divided into two characteristic forms-those resembling clouds or smoke, and those which present all the features of mighty eruptions. Sometimes one, sometimes another form will be most prevalent over a particular region of the sun's surface. When we study prominences of the latter form attentively we can scarcely doubt that they are really due to eruptions of glowing hydrogen. Now, if we assume that these eruptions are caused by an excessive pressure exerted on the hydrogen while yet beneath the sun's surface (and no other theory seems available, unless we abandon altogether the guidance of recognized analogies), we must suppose that there is a stratum partitioning off the inner masses of hydrogen from the hydrogen atmosphere outside the photosphere.

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The conception of such a stratum has been forced even on those who hold, like Respighi, that electricity causes these signs of eruptive action. But, adhering to the simpler and more natural supposition of a difference of pressure, we have the means of answering some very important questions respecting the temperature and physical

condition of the sun.

We have in the case of perfect gases :1st. The law of Mariotte and Gay-Lussac. 2nd. The constant ratio which subsists between the specific heat at constant volume and the specific heat at constant pressure.

This ratio, when once determined by recognized methods, for any gas, must be regarded as unchangeable-like the atomic weight of substances and other such constants. In order to deal with the eruptive prominences, as instances of the outflow of a gas from one space into another, we assume, for the sake of simplicity, that there is a constant pressure in both spaces, and neither gain nor loss of heat.†

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the ratio of the specific heat of the gas. to that of water.

the absolute temperature of the gas in the inner space.

the absolute temperature of the outflowing gas in the plane of the vent.

the pressure of the gas in the inner space. the pressure of the gas in the plane of the

vent.

Then according to the mechanical theory of heat, we have (on the assumed conditions)

v2

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r

a

=

the absolute temperature of the solar atmosphere assumed to be constant. = radius of the stratum separating the inner from the outer space.

=

=

specific gravity of mercury at the temperature of melting ice.

= 9. force of gravity at the earth's surface. = mean height of the barometer. the density of our atmosphere at the temperature of melting ice, and under the influence of gravity g, and atmospheric

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The heat-equivalent A may be put as 424 (taking the metre as unit of length, and centigrade degrees of heat). According to Regnault's latest results, x c is 3-409 for hydrogen; and according to Dulong, x for hydrogen is 1-411.

Zöllner here enters into a discussion of the probable value of r. From a consideration of facts already made public, he comes to the conclusion that the stratum which separates the inferior gaseous masses from the outer atmosphere must lie beneath the photosphere--which is the stratum where, through increased pressure, the spectrum of the hydrogen atmosphere becomes continuous. Taking the nuclei of spots as probably corresponding to the lower stratum, and the depth of such nuclei as 8", he suggests as a probable value for r,

(4) P. g, a, at (r + h) And in order to associate this formula with the preceding, we must assume 1. That the main portion of the solar atmo- or putting R sphere consists of the same gas which flows out to form the eruptive prominences.

2. That the absolute temperature of the solar atmosphere t is equal to the temperature to at the

level of the vent.*

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From this equation, if any three of the four quantities o, Pk, h, and t can be determined by observation, or shown to lie within certain limits, the fourth, or the limits between which the fourth lies, can be calculated. But the limiting values

of the quantities o, ph, and h can be determined

Zöllner infers the justice of the second supposition, from the fact that the bases of the prominences seem about as bright as the chromosphere. But though there is very little apparent difference, yet the photographs taken during the American eclipse indicate the existence of a real difference of brightness. For the edge of the lunar disc is eaten away, so to speak, at the bases of the prominences. It is true that Dr. Gould considers this is due to specular reflection at the moon's surface, but there is every reason to believe that Dr. Curtis is right in regarding the peculiarity as "a phenomenon of the dark room". e. a purely photographic effect. How ever, it is important to remark that Dr. Zöllner's results are not importantly affected by a change in the assump tions.-R. A, P.

T=

7=

=

R-8", where R sun's radius, 16' at the sun's mean distance, 15' 52"

Taking Hansen's value of the sun's mean parallax (8"-9159) we have

and

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↑ = 8" = H = Substituting these values in the expression for ti (when t = 0) we find

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These are minimum values of t for the assumed heights 1.5' and 3', respectively, to which the eruptive prominences are supposed to reach.

Zöllner here pauses to inquire whether the ascent of the prominence matter may not be due to the same principle which makes heated air ascend in a chimney, rather than to projection through a resisting medium. Of course, in the former case, his whole argument would fall to the ground, because instead of compressed hydrogen rushing out through an opening into a relatively rare atmosphere, there would be relatively rare hydrogen rising by reason of its lightness through a denser atmosphere. He rejects this conclusion, however, on account of the enormous velocity with which the prominences have been observed to rise-whether their formation is measured directly and timed, or by spectroscopic observations depending on the change of wavelength of light from prominence-matter moving towards or from the eye. He finds that the velocity of projectiont necessary to hurl matter

* In other words, Zöllner here assumes that the height to which the erupted gas is observed to be projected through the resisting atmosphere, is not very far less than that to which it would be projected by a like force, in vacuo. Owing to the probable compression of the erupted gas, the supposition is admissible, at least for the purpose of the above inquiry. The maximum rather than the mean height of the prominences should be taken, however; because obviously we cannot suppose all the observed prominences to be really projected from the edge of the disc, many must be joreshortened portions of prominences.-R. A. P.

Mr. Matticu Williams's, that matter is projected from the

I am led to notice here the amazing conception of sun far beyond the orbits of Mercury and Venus, and even beyond the orbit of the earth and Mars. It would not be difficult to show the enormous improbability that any explosive forces exerted by the sun could produce such results; but setting aside all such reasoning, and giving all due weight to the possibility of a tangential motion being imparted as well as a radial motion, it is certain that any bodies so projected must return to the point of projection. Setting aside the relatively minute effects of planetary perturbations, any body projected from the sun, even tangentially to his surface, must continue to have the place from which it was projected as a point of its orbit. Yet Mr. Williams gets his pro

jectiles altogether free of their source, and so makes them act all manner of unexpected parts. They become meteors, though the orbits of most meteors [ass

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to the observed height attained by the promiaences corresponds well with these observed velocities, whereas no such velocities could be expected if the hydrogen merely rose by reason of its relative lightness.

To resume, then, the consideration of the imiting values of t.

We can deduce a limit for t by discussing equation V. It may be readily shown that cannot exceed the mean specific gravity of the sun, or 1-46. Giving this value in V.; to a the value 40,690 deduced above, to h the value 8" at the sun's distance, expressed in metres, and top the baiting values 0-500mm and 0.050mm deduced by Wüllner, we get the following values for t. When ph 0.500mm t 0.050mm t Ph

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=

29,500°
26,000?

The mean value 27,700° will be adopted.

of the solar disc, or about 1-36th of the visible
solar semi-diameter.

This shows how quickly the pressure must in-
crease within the sun's globe, and justifies the
supposition that, even at the enormous relative
temperature undoubtedly existing, the so-called
permanent gases-hydrogen, oxygen, and nitrogen
for instance-can only exist in the form of glowing
fluids.*

A very surprising result follows, when we con-
sider in turn the case of a nitrogen or oxygen
atmosphere, having the same specific gravity and
temperature as the hydrogen atmosphere (at the
level of the dividing stratum), and reckon the
pressure existing in each atmosphere at that
height where the hydrogen spectrum begins to
become continuous. Taking the pressure of the
three atmospheres as equal to 184,000 atmospheres,
at a depth of 8" beneath the sun's visible limb, we
27,700°)

Now, differentiating equation V. with respect to get (with the temperature t =
do
d t

, the differential coefficient is found to be negative, that is, as o diminishes t increases. Therefore since the above value of t has been obtained by giving its maximum value, 27,700 is the minimum value of t. It corresponds to a value of 0.180 in for Ph; which value will acordingly be adopted in the following computa

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and pi Reckoning the depth at which in a fluid of specific gravity 1:46 the mere hydrostatic pressure would be pi, we find that this depth is 139 geographical miles, or about 650 English miles; that is at about 1-658th of the sun's semi-diameter,

1-46 seconds of are below the limb.

that they can travel in independent orbits around him.

= 180 millimetres

For hydrogen p

323

nitrogen p

1078

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So that the quantity of these two gases, on the above suppositions, may be regarded as absolutely evanescent where the spectrum of hydrogen begins to become continuous. This would also clearly be the case if we supposed the weight of the two atmospheres many millions of times greater, though it would only require that the weight of given quantities of nitrogen and oxygen should be 14 and 16 times (respectively) less than it actually is to cause these two gases, under the assumed conditions, to have a density coincident with that of the hydrogen at the sun's visible limb. It is easy to calculate, by means of formula III., and the known specific gravity of oxygen and nitrogen, how great the weight of each atmosphere must be in order that the density at a depth of 8" beneath the sun's limb may reach its maximum value 1·46. We thus find that the weight of the oxygen atmosphere can amount to but 0.56, that of the nitrogen atmosphere to but 0-64, where the weight of the hydrogen atmosphere is represented by unity.

as flowing either directly or indirectly from his
calculations:-
:-

1. We cannot conclude from the want of reztain lines in the spectrum of a self-luminons star that the corresponding elements are necesarj absent from its substance.

2. The layer in which the reversal of the spectrum takes place is different for ea stastance, and lies nearer to the centre of the star according as the vapour-density is greater and as the emissive power is less.

3. Under otherwise equal circumstances this stratum lies nearer to the centre as the intensity of gravity is greater.*

4. The distances separating the meal-strata of given substances, from each other well as from the centre, are greater as the tempore is greater.

the the

5. Under otherwise equal circumst spectra of different stars are richer in lower the temperature and the greater the suss of the star.

6. The difference in the intensity of t dark lines in the spectrum of the sun and sher stars does not depend only on the differez between the absorptive powers (of the correkeding elements), but also on the different depiz at which the reversal of the spectra in questa takes place.

Zöllner closes his paper by dwelling on great importance of distinguishing between the respective influences of temperature and presse on the spectra of gases and vapours. He points out the possibility that, when examining the spectra of electric discharges through rarefied gases, the pressure might be kept constant by an emission of gas before each discharge; and thus the means be obtained of determining the effect of temperature alone. He notes, however, that the results presented above could not be importantly affected by any change in the estimated pressure at which the hydrogen-spectrum becomes continuous, since, corresponding to limits of pressure proportioned as 1 to 10, the limits of the resulting temperature are proportioned as 1 to 1 only.

THE MICROSCOPE.-HOW TO CHOOSE
AND HOW TO USE IT.
(Continued from page 532.)

WE

the existence of disturbances in the solar atmo-
It appears, then, that putting out of question
sphere, the rays sent from the hydrogen which
exists at so great a pressure as to give a con-
tinuous spectrum, can pass through so small a
E do not propose any rigid order of sequence
quantity only of glowing oxygen and nitrogen, but we will endeavour to take the several pieces of
in our further notes upon the microscope,
that the absorption would be imperceptible, and
therefore (as we know to be the case) the spectro-apparatus as they appear to stand in the order of
scope could afford no sign of the presence of desirability. To this end we will allow ourselves
oxygen or nitrogen in the solar atmosphere.

lines.

Zöllner then presents the following propositions

considerable latitude in our interpretation of the However, as the absorption-lines of iron and word accessory, and include therein all apparatus other metallic elements show that we might (were not supplied with an ordinary student's micromere quantity in question) expect to find traces scope. And the question we will set ourselves to of the presence of oxygen and nitrogen, it is answer shall be, What extra apparatus, and in Even taking the case of a dense atmospheric necessary to add to the above considerations the what order, would you recommend to a student? shell of hydrogen, we find that for a temperature of circumstance that the permanent gases have but first place, partly because whether we do or no the I think we may place the polariscope in the 68,400 (t) we have a pressure of 4,070,000 slight emissive power compared with the vapours student is tolerably sure to do so, and partly atmospheres (p), only 27" beneath the visible limb of ordinarily solid bodies. The absorptive power because in proper hands it is an invaluable inbeing proportional to the emissive, we can under-strument of iesearch. In the form most commonly nowhere near the sun; they become asteroids-the gap stand (or at least it is no longer altogether per- applied to the microscope the polariscope consists of 157 millions of miles now separating the nearest plexing) that the lines of substances whose vapour of two parts-the polarizer and the analyzer. asteroidal orbit from the sun being seemingly as of no moment whatever. It cannot be too plainly insisted on density must be considerably greater than that block) that while the bursting of a planet into frag- spectrum, which yet shows no oxygen or nitrogen changed at pleasure. The polarizer and also the this projection theory having so often been a stumbling of oxygen or nitrogen should be seen in the solar These are precisely similar in construction and may (provided their fittings admit) be interments which eventually pursue independent orbits, or the projection of a body from a planet so that that body eventually follows an independent orbit, may be conanalyzer may consist of a rhomb of Iceland spar, or ceived (at any rate) as possibilities, the central body of a thin plate of tourmaline or of herepathite (somea system cannot possibly project bodies in such sort Against the supposition that such gases as oxygen, times called artificial tourmaline). On account hydrogen, and nitrogen can under any circumstances of its cheapness and freedom from colour, as well I do not say that the two former suppositions are one whit more acceptable than the latter. assume the liquid or solid condition, it has been objected as its greater freedom from danger of accidental There are abunthat all the gases which can be liquefied exhibit under damage, the Iceland spar is generally used, and in dant reasons for doubting whether a planet could burst in the way according to which the formation of the pressure a departure from the law that elasticity varies the form known as Nicol's prism. Instead of the asteroidal zone has been explained. Nor have we any able departure from that law, even under the greatest spar as a polarizer thin plates of glass may be with density; whereas other gases exhibit no apprecireason for believing that eruptive action on any planet could expel a body far enough to free it from the control pressure yet applied. But it is known that in the cases used, but as they do not permit of rotation readily of the planet, and enable it to follow an independent of the liquefiable gases the departure from the law in their disadvantages are great. The polarizer fits orbit around the sun. creases in a marked manner as liquefaction is approached. But we can conceive such things, It follows, therefore, that the appreciable departure into the stage from beneath, and it is well if a precisely as we can conceive (without believing) that the sun might project a body beyond the orbit of the pressure necessary to produce liquefaction bears a from the law under ordinary pressures only proves that bayonet catch or some simple appliance be arranged Neptune. What we cannot conceive, without forgetting measurable ratio to ordinary pressures. to hold it firmly in position. The prisms are the essential principles of dynamics and the law of It gives us gravity itself, is that a body projected to any distance promise, that is, of being able to liquefy such gases, a fitted into a collar, which rotates easily by a from the sun could ever be found travelling on an orbit promise justified by the event; and conversely, all that milled head, unless the stage be an elaborate which at no point approaches the sun.-R. A. P. is shown by the absence of any such departure from law mechanical affair, when special arrangements are in the case of other gases, is that the pressure necessary made to receive the prisms. The analyzer may All the quantities dealt with in equation V. are positive. Differentiating we getto liquefy them vastly exceeds any yet applied. The fact is suflicient to discourage any hopes we might have be fitted either immediately above the objective, formed that such gases could be liquefied by us; but by no in which position there is some loss of definition, means proves that they cannot, under any circumstances, assume the liquid or even the solid form. As a parallel or above the eye-piece, in which case there is a instance, we can conceive that no means would avail to considerable loss of field. In general work the produce variations of temperature many degrees on former position is the best. In any case the either side of the freezing point. In this case certain prisms should be made capable of rotation with exact centering. If it be desired to carry the

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analyzer above the eye-piece either tourmaline or herepathite should in all cases be preferred to Iceland spar. The price of a good polariscope and fittings adapted for a student's microscope varies from 30s. upwards. A selenite of some kind is almost a necessary accompaniment of a polariscope. Sometimes a thin film (to give red, yellow, or blue, according to fancy) is fixed in a collar and made to rotate with the polarizer. But this is a barbarous arrangement. In all cases the film of selenite should be mounted on a glass or in a brass slide, and some means adopted by which it may be removed from the field at pleasure without disturbing the object. It is also convenient to have three films giving different colours set in the same frame, their axes of polarization being in the same plane, that a series may be tried without trouble. A very efficient selenite stage has been described in a recent number of this journal, the price, however, is past a joke to most.

Having obtained the polariscope, the student, if he be a worker and use his "much, will find that he needs a steady and pure light such as is thrown upon the field by what is known as the achromatic condenser. This is optically little other than an objective of " or " focus made capable of approximation to the lower surface of the slide under view. It is a somewhat expensive piece of apparatus, costing from 30s. upwards. Mr. Brooke recommends a Kellner eye-piece in the place of the usual short focus objective. In any case the student may remember that he can always use his " objective as a condenser for his ", and so on. In this case he need only purchase fittings which need not be very costly. Mr. Collins has, within the last few years, introduced a new condenser, which he calls the Webster. From what we hear of it it seems a most efficient

affair, especially in connection with his adjusting diaphragın.

Mr. Swift has also introduced a popular and complete condenser, of which, as it is a perfect multum in parvo, we give a somewhat detailed description:- "It comprises an achromatic condenser of 90° angular aperture (this is suitable for all objectives from the 2in. to one-fifth), tinted ditto for correcting the yellow rays of artificial light, rack-and-pinion motion for focussing, a most effective spot lens, parabola, large diaphragm, carrying rotating cap-into this cap are fitted three discs for test stops-small diaphragm of apertures, polarizing prism, selenite diaphragm with two selenite films and clear aperture, and oblique light shutter for illumination with low powers.

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artificial light; also dispensing with the use of blue lamp chimneys.

"3. It is a very effective spot lens, and dark ground illumination with polarized light.

"4. An almost indispensable requisite for polarized light when using high powers with the object mounted in fluid.

"5. And not least important, the ease and rapidity with which the changes from ordinary to oblique, and plain or coloured polarized light with the other combinations I have named, can be made.”

Professor Beale recommends Lealand's Gillett condenser, but we have not space here to enter into a discussion of the respective merits of different makers of apparatus. It must suffice for us that we glance at every important accessory and give enough details to enable our readers to ask for what they want.

Our student will now probably seek to increase his "power." He can do this by the addition of a draw-tube to his instrument at the cost of a few shillings, but unless his lenses are very good this plan is not to be recommended. The drawtube in connection with an erector (for rectifying the inversion produced in the apparent position and movement of objects when they are viewed through a compound mirror) is, however, most useful, as it enables the observer to get a range of from four linear to 100 linear with an 8-10ths objective. Or he may add a C, D, E, and F eyepiece to his instrument, gaining in power approximately 1, 2, 4, &c. But the better plan is to get a C and then to add to his objectives first a ", 1-12th, 1-20th, or 1-25th to 1-50th, as he is able. But he will probably stop at 1-12th, and seek other accessories.

The optical combination is made with an angle of 90 or 120°, the former for objectives to the one-fifth of an inch, and the latter for those of in. There are two field lenses,' one of uncoloured glass for use with daylight, the other of a blue tint of sufficient depth to correct the yellow rays from an ordinary paraffine lamp, so desirable in long-continued study with artificial light. The condenser is attached to the stage of the microscope and held in its place by a bayonet catch, and the focus adjusted by a milled head with rack and pinion. The sliding frame has an open space and two spots, made central by a spring catch, and of a suitable size for the 2in. and lin. objectives, for dark ground illumination. The advantage of having these stops immediately beneath the lenses is very apparent in the much darker field that is obtained; their value also in this position is greatly enhanced by being able to use them in conjunction with the polarizing prism and selenite films, thereby bringing out in bold relief such balsam-mounted objects as the palates of the Mollusca. The rotating cap can be removed with the greatest facility and other stops substituted in the place of those (three) supplied with the instrument, as the nature of the test under examination may require. The use of the oblique light shutter and the small diaphragm of apertures are too obvious to require explanation. "With the exception of the frame of stops all the appliances are carried on the large diaphragm, and are brought into position by simply rotating that wheel until stopped by its spring catch. "If required, a parabola for dark ground illu

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an object placed at F will interrupt the rays and be strongly illuminated. A stop at S prevents any light passing through direct from the mirror, which is more adapted for high powers than the spot lens. Indeed, the latter cannot be used with what are properly called high powers.

The celebrated diatom prism which has reThe first thing will most likely be a mechanical cently caused such a sensation does not require stage, that is, a stage capable of movement in any explanation beyond this, that it is a rightall directions by means of milled heads. Their angled prism fitted either to the stage or on a forms are legion, every maker appearing to stand, and that its great advantages are that it have his special type. Let our student see enables us to obtain a beam of parallel rays of that whatever form he purchases possesses such intensity and in such direction as we require. the power of concentric rotation and that The goniometer for measuring the angles of the amount of movement can be read off ac- crystals we need not describe, as a well-concurately by a scale. He will now want a structed mechanical stage will serve most of its Maltwood's finder, a very simple and inexpen- purposes. Neither will we do more than mention sive arrangement for enabling a person to register Amici's prism for obtaining oblique light; and the position of any object in the field. It con- several other accessories but seldom used must sists merely of a slip of glass whereon is photo-be entirely passed over. graphed a series of numbers in squares thus

11 12 13 24 24 24

11 12 13 25 25 25

A little " stop" is placed at one end of the stage against which the end of the slide is placed. when any object of special interest is found the slide containing the object has to be removed and the "finder" placed in its stead and the numbers in the field read off and registered. It is obvious that the reverse process is simply to work the stage until the finder now comes into the field, remove the finder and place the object slide on the stage when the desired object will be found in the field. The price of a Maltwood varies from 5s. upwards. Substitutes have been proposed for the Maltwood, but the latter is so simple and inexpensive that we need not trouble to examine these.

Every observer ought to draw and measure his objects, but as this subject will come before us in another paper we will simply mention the names of the apparatus commonly used for these purposes. For measuring, either the stage micrometer or the eye-piece micrometer is used. For drawing, a camera lucida (a prism properly set), a neutral tint reflector, known as Beale's neutral tint, or a small disc of steel.

For "opaque" illumination we may use either the parabolic illuminator known as Crouch's but made also by several makers, or the side re, flector, or with very high powers Messrs. Beck'patent illuminator, whereby the objective is made its own illuminator by a most ingenious contrivance. The cost of all these is comparatively trifling. It strikes us very forcibly that we have spoken of nearly all accessories appertaining to the microscope proper. In our next we will hurry through such things as processes and mounting materials. If any reader wishes further information respecting any apparatus mentioned in this paper, perhaps the editor will allow him to ask any question he chooses.

H. P.

P.S.-In my last article I appear by some oversight to have said that a fair English 1 objective could be purchased for 50s.; I should have said 30s. I am pleased to learn that a London maker is selling a tolerably fair 1" for the astonishingly low price of 12s. As my cautio to our readers appears to have been misunderstood by some of the makers, I may, perhaps, be allowed to say that nothing was further from my intention than to reflect upon that most painstaking section; I merely wished to advise our readers to make as much as possible and to buy as little as possible. It is only just to our opticians to say that they are always willing to help the amateur to save his pocket if he will trust himself to them.

AND APPLICATION.

We have omitted to mention the spot lens-a simple and inexpensive, but very efficient means ELECTRICITY-ITS THEORY, SOURCES for procuring what is known as the dark ground illumination. This apparatus consists merely of a lens of moderate focus with a spot of black paper on its centre to stop out all rays except | those which pass through the periphery and con

mination with high powers is made to fit into the verge at so oblique an angle upon the object that 159.

place of the optical combination."

The writer of the paper published in the "Transactions of the Royal Microscopical Society (new series, No. 51, July, 1868, p. 110), claims for this condenser the following advantages, viz.,

"1. It can be used with marked advantage with objectives from 2in. to in.

"2. The remarkable daylight softness produced by the tinted field lens when used with

were it not for its refraction they would not enter the object-glass at all. Certain objects, such as diatoms, are seen by this mode of illumination brilliantly illuminated on a black ground. Mr. Wenham has introduced what is known as Wenham's paraboloid reflector. It may be easily understood by reference to Fig. which represents it in section A B C, and shows that the rays of light, rrr", entering perpendicularly at its surface, C, and then reflected by its parabolic surface,

BY J. T. Sprague.* (Continued from page 531.) THE SINE GALVANOMETER.— When a magnetic needle is removed from its normal position the force with which the earth's magnetic action tends to replace it is proportional to the sine of the angle of deflection. The deflecting force of a galvanic current has its greatest effect while parallel with the needle, hence if the current is made movable and follows the needle it moves till it can move it no further, these two forces balance each other, and it is *"Sigma."

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