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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.

-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 ? Also, how many sizes of watches do the trade ize?-B. E. LODDY.

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

-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 pipes ?-T. W. C.

7.]-TO "INDUCTORIUM."- Will "Inducto'state the size of secondary wire he uses? and as I allows fin. between the discs, must it be wound vards and forwards in this space until filled, and the next, and so on ?-T. W. C.

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 enabling me to wash the work when done ?-THOS. PRIOR.

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 and then put into bottles with sweet oil, tying over some perforated paper.

ents give me instructions and drawings for making that will have the same effect as varnish on paint, boiled but the garlic; let them stand for a day or two,

98.)-SPECTROSCOPE.-Can any of your correctroscope ?-T. W. C.

99.]-SCIENCE AND ART EXAMINATIONS.I ask Mr. G. E. Davis what books he would recom1 to one preparing for the Organic Honours Paper, xt May's examinations?-CROW TREES. 00.]-COPIES OF COINS IN ELECTROTYPE. some kind brother please tell me how to take of coins, &c., in electrotype?-WILLIAM S.

8

CHER.

01.]-CLEANING COINS.-Will you or one of your y readers please to inform me how to clean old =(silver and copper) without injuring the coins?LIAM S. FLETCHER. 02.)-TRUE

HEART FOR TRAVERSING.-I ld be grateful if any one would inform me, by a 1 sketch or otherwise, how to describe a true heart traversing purposes, from lin. to 3in.-GOOD

DS.

703.]-CHANGE WHEELS.-My thanks to "B. H." is answer to query 4871, p. 454, but he evidently akes what I want. He gives me an answer to age from oue hank to another. I want to know how - find the proper wheels in the first instance. I e never seen a rule myself, and don't know whether e is one or not. If “B. H." could assist me any her I should be obliged.-GOOD WORDS. 704.]-CHANGING SURNAME.-I wish to change

surname. How can I do it ?-M. SPIEGELHALTER. 705.]—NATURALIZATION.-What steps must I to become a naturalized Englishman?-M. SPIEGEL, 706.]-PHOTOGRAPHY.-I put the water that I h the silver prints in into a deep mug and precipitate silver with common salt, and have done so with the test success for two years. The silver precipitated utifully, but now it is just the reverse, it won't pertato at all, and I have put lots of salt in, but to no l. 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.

707.]-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 sure of 401b, 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.

[4719.]-ELECTRO PLATING.-Will some brother reader kindly inform me how I can electro-plate small articles so that they may keep their colour? The articles are brass and copper.-SCRAWLER. [4720.]-KALEIDOSCOPE.-Will any of our optical friends tell me how to make a kaleidoscope such as I see in the shop windows; I don't mean the common ones?-H. K. L.

whether I can obtain many fossils in the neighbourhood [4721.]-FOSSILS.-Will Mr. Underhill tell me 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.

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

4224;

4708.]-LOSS OF VOICE.-For the last two or three
-rs my voice has been very husky and indistinct, and
ave generally to give a short cough before I can
ak a word. I shall be very glad if some kind reader
1 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-hours with the Telescope," p. 17, and say
4265
ether he thinks it would be suitable for an instru- 4266
nt 4in. aperture 5ft. long? I wish to make a stand 4269
ch shall give a steady motion, and be easily moved 4284
a place to place. Perhaps Mr. Proctor's experience 4286
y enable him to suggest some simpler plan that would
noderately efficacious.-TURTON.

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.

4287

Cotton Spinning, 406.

4288

47101-FASTENING BRASS TAPS IN KITCHEN 4293
ILER.-Can any of your numerous readers inform 4294
how to tighten a brass tap to kitchen boiler that has
come loose ?-INQUIRER.
4711]-COLZA OIL.-Will any brother reader be
ad enough to instruct me how to test the quality of
za oil.-M. Q. W.

4292

Force Pump for Irrigation, 406.
Millers, 406.
Friction in Steam Cylinders, 406.

Brewing, 406.

4299

Silvering Clock Dials, 407,

4300

Sausages, &c., 407.

4302

Madagascar Matting, 407.

4303

Cast-Iron, 407.

4308

Model Mills, p. 430.

4310

4312

4712.]-AIR v. STEAM.-I want to substitute air 4311 steam (like many others I suppose) but there is supposed impossibility to contend with-namely, 4315 t it requires just as much power to force the air into 4317 boiler as it does to move the engine. Now if 4326 difficulty could be overcome, could any correspon- 4327 t tell me, if air even then could cope with steam?-4331

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4713.1-BEES.-I wish to remove my hive inside a ding during the winter. Can any reader inform me e bees would pass in and out through a small hole de in a 9in. brick wall, and how bees are fed, or what ould feed them with in the winter? I think a few ers on bees, through the MECHANIC would be found y acceptable to many of its readers.-J. G. 714.]-HOT OR COLD BATH.-Can any reader give information on the following points? 1st. What Bus could I adopt in order to get hot water from a

4332 4333 4337

Emigration, 430.
Destructive Soap Powders, 439.
Rocking Chair, 480.
Cleveland Ironstone, 430.
Sizing, 430.

Polariscope for Lantern, 480.
Want of Pressure, 430.
Stone for Trinkets, 431.
Black Glass of Antimony, 430.
Lancashire Black, 430.
Hollow Candles, 430.

4338 Draught Furnace for Smelting Lead Ore. 4339 La Crosse, 430.

4343 Windmill for Working Lathe, 431.
4345 Cracked Boiler Plates, 481.
4346 Concertina, 431.

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

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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.

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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 Böttger, 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 ordinary 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 zinc 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

576

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 ? Wo, 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 By dipping any bad odour is effectually destroyed. it into hot water, and covering it with oil silk, a convenient antiseptic poultice is formed, easily made, very It thus light, and answering perfectly its purpose. supersedes the use of lint, ointments, and linseed-meal or bread poultices. It is easily burnt-no small advantage 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 advantage. 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 of the method now followed by Messrs. Riche and Champion, for making the sound-producing instruments alluded to, which consist of an alloy of 80 parts of copper and 20 of tin, which is hammered out with fre

fectly true: but the fact is, that no simple substance
The most nutritive
given alone will support life.
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.

SCAVENGER BEETLES.-Scavenger beetles are to
be seen wherever the presence of putrescent and offen-
sive matter affords opportunity for the display of their
repulsive but most curious instincts; fastening on it
with eagerness, severing it into lumps proportionate to
their strength, and rolling it along in search of some
place sufficiently soft in which to bury it, after having
I had frequent
deposited their eggs in the centre.
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
add to their diet by a more liberal use of harmless salad
herbs which are now altogether wasted. Watercress is
very well in its way, but is not everywhere accessible.
It has lately been pointed out that our sorrel plant is a
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.

sea-cu

The Sixpenny Sale Column is the only plasË –
appear queries sent by J. E., Li, J
S. R.

W. J.-We cannot give the addresses of con
If you wish for the address of the restle
you had better ask for it throath T
Column.
take to receive the specimens.
AN ASSOCIATE OF R. S. MINES.-We
much labour.

J. GILLAIRD.-The ENGLISH MECKLE
for the purpose of advertising gre
a "remuneration for their ideas
we seldom receive letters like you
WORKMAN.-We
A BRITISH
There will ru
direction indicated.
In & mentass
ones on the look ont for flats.
the weaker party should be doubly.
A BLACKSMITH.-The following a
you ask for :-A Millimetre = 009 Ce
metre 0-3937043in.; a Decime
Metre 39-370432in., or 3-2808/BIL, AA;
8 Kilometre = 1093-6251 yards; =
6-21377 miles.

A. ALLEN.-We do not think it would ne
pearance of our journal to insert par
They are to all
among the matter.

poses advertisements, and should se with the volume. HESPERUS.-If your claim has been ar probably share in the settlement which he -58. in the pound, we believe. D. F. A.-We cannot give the information ne ment Column was designed to meet casesia H. B.-Fecula is a term sometimes applia, sometimes to cornflour. The most ordinary is a pulverulent ma ter obtained by breskar texture of plants, washing with water, and m the deposit.

EMERY.-B. J. (Birmingham)-Na. Faery is t granular, or compact variety of a mineral, tra corundum. It takes its name from Cape Em island of Naxos, where it is found in abundants whence it is largely imported.

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

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

JOHN HAMPDEN (Wilts)-Fe cannot fesert advertisements on condition of any ons screpting your challenge and overturning year theories. CRYPTOGRAPHER.-Next week

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

quent annealing. An 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 fr b

answers better, and can be rolled out. The process is similar to that in use in China, and is carried out Paris by M. Cailar.

at

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, common 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 Umbellifers are amongst the most dangerous of British plants.

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.

A

ARTIFICIAL BUTTER.-Apparently astonishing as the idea is, the manufacture of artificial butter (beurre artificiel) is seriously contemplated in France. 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 cxtracted 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

SEA CUCUMBERS. The holothuriæ, or
cumbers, may be regarded in one light as soft sea-
urchins, and in another as approximating to the anne-
lides or worms. Their suckers are similar to those of
the true star-fishes and sea-urchins. Besides progression
the extension and contraction of their bodies. The
mouth is surrounded by plumose tentacula, the number
of which, when they are complete, is always a multiple
They all have the power of changing their
of five.
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 them-
selves 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 re-
markable parasite, a fish belonging to the genus Fier-
asfer and about 6in. long. This most impudent and in-
trusive 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 choos-
ing this strange abode is yet an enigma.-Dr. Hartwig's
"Sea and its Living Wonders."

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. Jarman,
Jos. Mosley, J. D., J. Lee, Paddy, J. Bowley, Compen-
sated 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.

reply on melting cast steel.

ometers is an advertisement, and therefore
AN ENQUIRER.-Your query about price, &an di tan
serted.

SCREW POWER, BY J. K. P.-Next week.
LEX.-You find fault with the style of writing
correspondents, and fall into similar error you
You accuse "R. P.," in his letter on Artne
charges, of" deliberate equivocation," and co
by saying that his letter "proves nothing b
own ignorance." Your reply to Scriptor
same style. One way to improve others is tem
example ourselves.

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.
for the Continent, but of no service to
BERNARDIN.-Your suggestion for a passport b
mechanics.

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

J. BASKERVILLE on "Link Motion," next

THE PHANTOM WHEEL.-We have rec71.25 of

letters on this question in answer to the

Blacksmith," all testifying to the in of his

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from the letters.

A. G. V. GOODEUR.-Send us the best you can.
ORGAN BUILDING.-"R. W. D." and others
"Adept." The last we heard of our esteem!?
spondent was that he was unwell, but that be
soon to be able to continue his papers.
heard, we fear he is not recovered. It wo
that Mr. Kimble, another able corresp
organ building, wrote us about ten weeks since
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 "Painti
Decoration " now appearing in the Building Nes-
J. M.-Isocheimal means "equal winters;" ..
the same mean winter temperature. It is fr
Greek-isos, equal; cheima, winter.

R. E. Y.-"Bouheyl" is a mining term and sign
living stream. It is applied by tin miners to ac
tion of a rock which is impregnated with tin.
S. R. B.-The pancreas is a fleshy gland situated 4)
and behind the stomach, secreting a saliva-like
which assists digestion. The literal meaning
word is "all flesh."

The English Mechanic

AND

IRROR OF SCIENCE AND ART.

FRIDAY, SEPTEMBER 9, 1870.

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. 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 ll our readers, they will be acceptable to many. The results to which they lead can hardly fail to De generally interesting.

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.

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 recog=nized 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.f

Put

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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 t.

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

σ =

:

ρ Pi α, α ti

.

(3)

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

h

Ph

t

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from the outer space.

specific gravity of mercury at the temperature of melting ice.

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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As the density of the solar atmosphere at moderate distances from the sun has been shown to be almost evanescent, we may, for simplicity, assume that H is equal to the mean height of the eruption prominences.*

Many prominences 3' in height have been seen. But let us take H at only 1.5'. 1

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, R-8", where R sun's radius,

(4) p. 9, 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 16' at the sun's mean distance, 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

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m for

g 9.p

Ρ

and

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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.

of the quantities σ, ph, and h can be determined Mr. Mattien Williams's, that matter is projected from the

* 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 are not importantly affected by a change in the assump ever, it is important to remark that Dr. Zellner's results tions.-R. A, P.

+ 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 projectiles altogether free of their source, and so makes them act all manner of unexpected parts. They become meteors, though the orbits of most meteors pass

to the observed height attained by the promiRences 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 himiting values 0-500mm and 0.050mm deduced by Wüllner, we get the following values for t. 0.500mm t 29,500° 0.050mm t 26,000

When ph
Ph

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=

=

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 consider 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 =

ασ
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 R for Ph; which value will acordingly be adopted in the following computa

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Ph 0.180m we get

=

=

=

Pa 184,000 atmospheres, and pi €4,070,000 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,

or 1.46 seconds of are below the limb.

Even taking the case of a dense atmospheric shell of hydrogen, we find that for a temperature of 68,400 (t) we have a pressure of 4,070,000 atmospheres (p), only 27" beneath the visible limb nowhere near the sun; they become asteroids-the gap

of 157 millions of miles now separating the nearest
asteroidal orbit from the sun being seemingly as of no
moment whatever. It cannot be too plainly insisted on
block) that while the bursting of a planet into frag-
this projection theory having so often been a stumbling
ments 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 con-
zeived (at any rate) as possibilities, the central body of
a system cannot possibly project bodies in such sort
that they can travel in independent orbits around him.
I do not say that the two former suppositions are one
whit more acceptable than the latter. There are abun-
dant reasons for doubting whether a planet could burst
in the way according to which the formation of the
asteroidal zone has been explained. Nor have we any
reason for believing that eruptive action on any planet
sould expel a body far enough to free it from the control
of the planet, and enable it to follow an independent
orbit around the sun. But we can conceive such things,
precisely as we can conceive (without believing) that
the sun might project a body beyond the orbit of
Neptune. What we cannot conceive, without forgetting
the essential principles of dynamics and the law of
gravity itself, is that a body projected to any distance
from the sun could ever be found travelling on an orbit
which at no point approaches the sun.-R. A. P.
All the quantities dealt with in equation V. are
positive. Differentiating we get-

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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.

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
quantity only of glowing oxygen and nitrogen,
that the absorption would be imperceptible, and
therefore (as we know to be the case) the spectro-
scope could afford no sign of the presence of
oxygen or nitrogen in the solar atmosphere.

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-luminous star that the corresponding elements are necesar absent from its substance.

2. The layer in which the reversal of the spectrum takes place is different for ei saastance, 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 real-strata of given substances, from each other well as from the centre, are greater as the temature is greater.

5. Under otherwise equal circumstag the spectra of different stars are richer in the lower the temperature and the greater thnaso

of the star.

6. The difference in the intensity of det dark lines in the spectrum of the sun and Sher stars does not depend only on the differey between the absorptive powers (of the corresading elements), but also on the different dept at which the reversal of the spectra in quan takes place.

Zöllner closes his paper by dwelling on the great importance of distinguishing between the respective influences of temperature and pressu 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.)

W

E do not propose any rigid order of sequence in our further notes upon the microscope, but we will endeavour to take the several pieces of apparatus as they appear to stand in the order of desirability. To this end we will allow ourselves 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 necessary to add to the above considerations the what order, would you recommend to a student? 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 slight emissive power compared with the vapours student is tolerably sure to do so, and partly 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 stand (or at least it is no longer altogether per- applied to the microscope the polariscope consists plexing) that the lines of substances whose vapourdensity must be considerably greater than that spectrum, which yet shows no oxygen or nitrogen of oxygen or nitrogen should be seen in the solar

lines.

Zöllner then presents the following propositions

Against the supposition that such gases as oxygen, hydrogen, and nitrogen can under any circumstances assume the liquid or solid condition, it has been objected that all the gases which can be liquefied exhibit under pressure a departure from the law that elasticity varies able departure from that law, even under the greatest with density; whereas other gases exhibit no apprecipressure yet applied. But it is known that in the cases of the liquefiable gases the departure from the law in creases in a marked manner as liquefaction is approached. It follows, therefore, that the appreciable departure from the law under ordinary pressures only proves that the pressure necessary to produce liquefaction bears a measurable ratio to ordinary pressures. It gives us promise, that is, of being able to liquefy such gases, a promise justified by the event; and conversely, all that is shown by the absence of any such departure from law in the case of other gases, is that the pressure necessary to liquefy them vastly exceeds any yet applied. The fact is suflicient to discourage any hopes we might have formed that such gases could be liquefied by us; but by no means proves that they cannot, under any circumstances, assume the liquid or even the solid form. As a parallel instance, we can conceive that no means would avail to produce variations of temperature many degrees on either side of the freezing point. In this case certain peculiarities noticed in the expansion of water with such to inter that iron or gold, which exhibit no such peculiarivariations of temperature might lead the experimenter ties under changes of temperature, cannot be liquefied. The conclusion would be erroneous, as probably is the above inference respecting gases.-R. A. P.

of two parts-the polarizer and the analyzer.
changed at pleasure. The polarizer and also the
These are precisely similar in construction and
may (provided their fittings admit) be inter-
analyzer may consist of a rhomb of Iceland spar, or
a thin plate of tourmaline or of herepathite (some-
times called artificial tourmaline). On account
of its cheapness and freedom from colour, as well
as its greater freedom from danger of accidental
damage, the Iceland spar is generally used, and in
spar as a polarizer thin plates of glass may be
the form known as Nicol's prism. Instead of the
used, but as they do not permit of rotation readily
their disadvantages are great. The polarizer fits
into the stage from beneath, and it is well if a
bayonet catch or some simple appliance be arranged
to hold it firmly in position. The prisms are
fitted into a collar, which rotates easily by a
milled head, unless the stage be an elaborate
mechanical affair, when special arrangements are
made to receive the prisms. The analyzer may
be fitted either immediately above the objective,
in which position there is some loss of definition,
or above the eye-piece, in which case there is a
considerable loss of field. In general work the
former position is the best. In any case the
prisms should be made capable of rotation with
exact centering. If it be desired to carry the

If r be the radius, s the specific gravity of a star supposed uniform, the intensity of gravity at its surface varies as .-K. A. P.

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 diaphragm.

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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.

"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 illumination with high powers is made to fit into the 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

artificial light; also dispensing with the use of A B, to a focus at F, can form no part of the blue lamp chimneys. largest pencil of light admitted by any of the "3. It is a very effective spot lens, and dark object-glasses, and represented by G FH; but 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 acces sory 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.

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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 recently caused such a sensation does not require any explanation beyond this, that it is a rightangled prism fitted either to the stage or on a stand, and that its great advantages are that it enables us to obtain a beam of parallel rays of such intensity and in such direction as we require The goniometer for measuring the angles of crystals we need not describe, as a well-constructed mechanical stage will serve most of its purposes. Neither will we do more than mention Amici's prism for obtaining oblique light; and several other accessories but seldom used must

The first thing will most likely be a mechanical stage, that is, a stage capable of movement in all directions by means of milled heads. Their forms are legion, every maker appearing to have his special type. Let our student see that whatever form he purchases possesses that the power of concentric rotation and the amount of movement can be read off accurately by a scale. He will now want a Maltwood's finder, a very simple and inexpensive arrangement for enabling a person to register the position of any object in the field. It consists 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.

vance.

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 contriThe cost of all these is comparatively trifling. It strikes us very forcibly that we have spoken of nearly all accessories appertaining to In our next we will the microscope proper. 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.

that 159.

AND APPLICATION.

BY J. T. SPRAGUE.* (Continued from page 531.)

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 conTHE SINE GALVANOMETER.verge at so oblique an angle upon the object that | When a magnetic needle is removed were it not for its refraction they would not from its normal position the force with which enter the object-glass at all. Certain objects, the earth's magnetic action tends to replace it is such as diatoms, are seen by this mode of illumi- proportional to the sine of the angle of deflection. nation brilliantly illuminated on a black ground. The deflecting force of a galvanic current has its Mr. Wenham has introduced what is known as greatest effect while parallel with the needle, Wenham's paraboloid reflector. It may be easily hence if the current is made movable and follows understood by reference to Fig. which represents the needle it moves till it can move it no further, it in section A B C, and shows that the rays of these two forces balance each other, and it is light, rrr', entering perpendicularly at its surface, C, and then reflected by its parabolic surface, *"Sigma."

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