understood that the gas-engine differs very considerably from the hot-air engine, and that there are certain chemical phenomena attending the combustion of the gases that require explanation. We cannot do better than refer to the recent experiments made by MM. Berthelot and Vieille published in a recent number of Comptes Rendus), who have made a study of the phenomena arising 'rom the ignition of explosive mixtures.

A series of 250 experiments were made, comrising 42 distinct explosive mixtures, embracing ot only mixtures of oxygen with hydrogen, caronic oxide, and marsh gas, pure and mingled with itrogen-mixtures already examined by MM. unsen, Mallard, and Le Chatelier; but also mixires of oxygen with two combustible gases at a me were tried-such as carbonic oxide and hydroen, &c. The following are results of observed ressures produced by the explosion of gaseous ixtures, reduced to the datum before combustion 0°C. and 760mm. mercury, and assuming that e loss of heat by conduction is inappreciable. MIXTURES OF HYDROGEN AND OXYGEN. 1. H2+02 9.80 atmospheres. 2. H. +

+ H 8.82

3. H

2H, 8.02

20. C.Na+ 2N2O2 = 26·02 atmospheres. highest pressure that was obtained with ous mixtures at the normal initial pressure. f the whole series of explosive mixtures exmented with, those numbered here 1 to 19 are ted to the compounds contained in mixtures of gas and air. The results given are means calted from the pressures of vessels of different cities, and reduced to a standard that would ally apply in the case of a vessel of infinite city that is to say, to the theoretical case of xplosion with a constant volume, and without Eof heat by the sides of the vessel.

388.

With pure gases of oxygen and hydrogen, when volumes were equal No. 1, the maximum effect obtained. In Nos. 2, 3 and 4, as the oxygen further diluted with hydrogen, the pressures e gradually less. The hydrogen was in excess. Nos. 5 and 6 the hydrogen was diluted with gen with the same result. The oxygen was in In Nos. 7, 8, 9, and 10, the mixtures of rogen and oxygen were diluted with nitrogen, increase of nitrogen reducing the pressures. To. 11, a mixture of carbonic oxide and oxygen, e a pressure of 10-12 atmospheres, the maxim effect. To this mixture, nitrogen was added h a decrease of pressures in proportion to the ntity of nitrogen added, showing the effect duced when an inert gas is present. fixtures of carbonic oxide, hydrogen, and oxyNos. 15, 16, 17, and 18, should be the same the mean of the two simple explosive mixtures s. 1 and 11; but they are lower, especially No. because the hydrogen burns more quickly than carbonic oxide, and the maximum pressure s not show the simultaneous combustion of the

OLARISER FOR THE MICROSCOPE. 22645.]-HAVING fitted up a polariser on my roscope in a (to me) new method, which has ved very handy in practice, I take the liberty of Hing you a description of the device for the efit of any readers of "ours" who may wish to pt it. It is not patented. I bought the prisms self, choosing a rather small one for the analyser a small one for the polariser. The small prism d fitted in a tube that was just large enough to

Fig.1.

Fig. 2.

within the tube, thus, Fig. 1, analyser in position;
Fig. 2, out of position.

contain it, leaving no spare room. This tube IA row of holes was now made along each side of placed on a swivel inside of the microscope tube just the open part in. from edge, and about in. above the nose-piece, in such a way that it can be asunder; wires passed through, cut to length outbrought exactly over the aperture in the nose-piece, side, and fixed by a drop of solder at each end; or pushed over to one side out of the way, but still another set of wires was now put across the first set, being passed alternately under and over them, and one end of them being soldered to the narrow turndown on the low or upper end of the body, and the other end being turned round the lowest cross wire. Tinned or galvanised wire should be used, two pieces of iron hoop, galvanised if it can be got, and a piece of timber 3ft. 9in. long, and 1in. square (mine is ash), are now required. The hoops are riveted round the body of the extractor, about 3in. from each end, care being taken that the projecting ends of the hoops are exactly the same length, and these ends are screwed to two opposite sides of the stick, so that one end of the stick projects about 24in. below the lower end of the body of the extractor. In practice, the hoops should be partly riveted to the body before the wires are put into it; two rivets should be put into each hoop through the back of the body; then, after the wires are soldered at each side, a rivet should be put through the hoops at each side, and the fin. edge projecting above the wires, and then the ends of the hoops screwed to the stick. A round iron spike should be fixed into the lower end of the stick, and about 4in. cut off the upper end, a hole bored lengthways through this piece, a piece of round iron fixed in the upper end of remainder of the stick, the cut off piece put on the iron, the hole being large enough to turn very freely on the iron, and then a washer put on and the iron riveted over it, but very loosely, so as to have the loose handle spin freely on the iron spindle. The angles of the loose handle and the upper part and lower end of the stick should be chamfered off. A centrebit pole in. in diameter was now cut in the upper end of the body with one side of it exactly flush with the centre of the back, and the extractor was finished.

A small lever on the end of the swivel comes
through the microscope tube, by the aid of which
the analyser can be moved from the outside.
The large prism is also mounted in a small tube
and placed at the end of a short arm below the
stage, in such a position that it can be pushed
backward in a line with the stage aperture, or for-
ward, out of the way, but still protected by being
under the stage.

By this arrangement, the polarising apparatus
can be instantly thrown into position by two
motions, one for each lever. (It takes only one
second by actual trial).

Of course, this device can be applied only to
microscopes that have a wide tube; but it can be
modified to suit others with narrow tubes by
adding a "bulge" or recess, into which the
analyser can be pushed when not in use.

The whole device has proved so exceedingly con-
venient, and is so highly approved of by all the
members of our club, where I exhibited it last
night, that I am in hopes it may be of some use to
the fraternity.
Geo. B. Scott.

Brooklyn, N.Y., April 2nd.

BEE-KEEPING.
[22646.]-IN answer to J. Perry (letter 22602),
the radius of circle in which the comb revolves in a
6in. or 7in. measured to centre of comb, and in the
single-comb extractor, as illustrated at p. 146, is
more complete double-comb machines 54in. to 6in.
A. I. Root, the American bee-man, sums up the
disadvantages of revolving-can extractors thus:-
"Experiments have been made almost without
number, and the general decision now seems to be
in favour of a machine made entirely of metal, with
everything stationary about it except what must be
revolved. The momentum of heavy metal re-
volving cans, or of honey after it has left the comb,
defeats the very object we have in view, and nothing
will so effectually convince one of the difference as
an actual trial of the two machines side by side.
With the light all-metal, machines (in which the
can is stationary) the comb is revolved at the speed
required almost instantly, and as soon as the honey
is out of the comb the operator is aware of it by
the decrease of weight as he holds the crank in his
hand; but with the revolving-can machines the
stopping and starting take more time than doing
the work."

This extractor was made and used last year, and answered as well as anything possibly could. It would be, I think, an improvement to have it made so as to have the wire grating on an independent frame, so as to open, and I do not think it would be at all hard for anyone who was making one to make that alteration in it. I dare say other improvements could be made in how it was made, as it; but such as it is I described it and no one has given any thing better, and it certainly will do very well for want of better. The materials can't have cost town in Ireland, the other things I had. They more than 18. 3d.: the tin cost 9d. in a country were 6ft. of hoop, 12 yards of wire, the bit of timber, 8 rivets and 8 screws, 9in.in. round iron, and a small washer.

of foundation; that is, to within fin. of bottom of
"O. V." will find it pay well to use full sheets
frame, except in a few frames, to leave a little
room for the bees to make drone comb.

close without expressing my extreme delight (which
As I am writing to the "E. M.," I really cannot
I am sure is shared by very many others) at Dr.
Allinson having at last brought down on himself
two writers so uncommonly well qualified to show
him up as "F.R.A.S." and "Sigma," to say
nothing of common-sense
have undoubtedly done good service to the readers
"Housekeeper." They
of the "E. M.," and, being an Irishman, I cannot

I can thoroughly endorse this, having made and
used both forms of extractors; the ordinary double-help wishing "more power to them." G. J. H.
comb machine, which costs about 30s., is far easier
and more convenient to work than Abbott's
pattern, illustrated at p. 146.

Alfred Watkins.

[22647.]-As the question how to make a one-
comb extractor has been asked a second time, I will
try to answer it as well as I can. The home-made
one which I am about to describe was made without
having ever seen one.
the advantage of a pattern, or even of the maker
sheets of tinplate, one 14in. by 20in., the other
The body is made of two
14in. by 10in. The large sheet was bent length-
ways into a segmental form, so as to be about 9in.
across the open, and a hem turned on each of the
long, straight sides. An end was now cut from the
small sheet to fit this, so that when the seg-
mental edge was turned down to fit over the end of
along the straight side of the end, the end mea-
the body, and about in. turned at right-angles
sured 3in. in the middle. This was soldered on to
the end of the body, leaving fin. of each long side
of the body projecting above it, which were parallel
to each other, not parts of a segment. The other
end was now cut to fit the body, but made long
enough to come up to the top of long sides of body,
and turn up at right-angles 4in. upon those long
sides. A hem was put on the straight side, all the
other edges turned down, and it was soldered on to
its place, thus forming a sort of can 44in. deep at
one end of the body of the extractor. I
should have said that the hem on the long
sides of the body was made only along
the open part; the sides of the closed 4 in. at
the lower end were left standing to the full height.

BEE-KEEPING-CRUSHED FINGER

NAIL.

[22648.]-I AM sorry to say that I have not yet got sufficient experience to be able to tell Mr. Perry the best time to put supers on his hives. Mr. Prentice or "J. I. S." should be able to give some information, and I hope will do so, as I would be glad of a little myself. I know in a general way that a good deal depends on the strength of the worked up by stimulative feeding, spreading brood, stock; if it is weak after the winter, it must be and increasing the size of the brood nest; and then when you have 8, 9, or 10 frames (according to size of hives and situation) full of bees, you can put on your super, or put in your section frame, as soon as there is a good supply of honey coming in. I believe it is a great and a very common misfew bees and too small a brood nest, and the time take to try to commence working supers with too spent in the beginning of the season in strengthening the stocks and increasing the size of the brood nest is far more than made up for in the final result. I have confined myself to the general principle on which I intend to act; but have very little idea when exactly I will be able to put on supers myself, but I will not do so early, as I have only three stocks-very good ones, however-and I want to work them up very strong, and take early swarms from them. One of them is a stock of beautiful pure Ligurians, from an imported queen, and I intend to Ligurianise the others, which will cause more or less loss of time in putting on supers. If "J. I. S." or Mr. Prentice would give me some practical hints, I should feel very much obliged.

Das is the first spring I have had bees in barframe dives, one of my stocks having been a swarm what I got ast July, and into which we put a Laruan queen on the 10th of Oct. last; the others are formed of dees driven from neighbours very late kast autuma, which we had to set up with founJaton and syrup; but we made them fine and strong, having put the bees of four hives into one, sad of three into the other; they continued breeding very late, and commenced very early this ng, and have now a lot of brood sealed in the se cells, out of which a former lot have come already this year.

I cannot imagine what fault Mr. Perry can find with the feeders which I described; they seem to mess nearly perfect as possible, and the easiest possible things to fill and manage. I have never used or seen those described by Mr. Green; but from the description I would much prefer my own. As to Mr. Perry's suggested modification of the at feeder, it is rather hard to tell how it would act practically: but as he has the feeder it would be very easy to try. It would be worth his while to do so, and I should say he could do no harm, and I hope he will let us know the result. The theory seems right enough. If I had seen "J. I. S.'s" letter about the extractor in time, I would not have

med writing the one which I sent last week too iste for last E. M."; but it may be useful in helping amateurs to put one together. It is, I ought to say, intended for use with standard size bar

frames.

I hope very much that Mr. Prentice will give us more of his very interesting and useful practical experience, and keep us posted up as to what he is ang during the approaching season. There is one thing which I cannot quite understand; if his bees were not fed in the autumn, and did not get or cake under the quilts, how did they use over b. of sugar per hive? Mine, that had to be fed beavily last autumn, have used only 621b. altogether up to the present, 55lb. of that in autumn.

-J. L.'s method of treating a crushed fingermal is very good-in fact, the best. I do not, however, think the water was too hot-it can't be too hot, if it does not actually scald. I would add just one little thing; the instant you crush your had put it into your mouth, and don't take it out till you have the hot water ready to put it into. G. J. H.

[52873.]-Cough Cure.-In reply to a late in- [53214.]-Agricultural Holdings Act-E quiry, the following is said to be most efficacious the number of lines occupied by this querie and of universal service :-Take 18oz. of perfectly might have given the context, or perhaps the we sound onions, and after removing rind make several clause. In its absence one can only suggest the incisions, but not too deep. Boil together with "pastoral" means something relating to shepher 13 oz. of moist sugar and 2 oz. of honey in 350z. or to the rearing of stock.-DICTIONARY. of water for three-quarters of an hour; strain, and fill into bottles for use. Give one tablespoonful of this mixture (slightly warmed) immediately on attack, and then, according to requirement, five to eight half tablespoonfuls daily. It is said that this recipe was that used by the Zulu Caffres when visiting Europe some two years since, and who suffered much from the climate, but invariably recovered upon its use. The same results have in all cases been observed when used by others. Extract from "Veg. Rundschau."-MARIENBERG.

[53088.] Steam-Heated Kiln. I note "Essar's" reply to my query. He considers it a peculiar query; but I must say his reply is far more peculiar than the query, and if that is a sample of "Essar's" replies, he ought to stop. I with wood fuel, and also that since writing the wish to inform "Essar" that steam can be made query, I have found that several engineering firms has been constructed and is at present in use. have tried it, and that "such an unlikely thing"

R. E. S.

[53174.]-Transposing Tunes.-Here is a plan
so very simple and easy that it will enable the
merest tyro, on the first trial, to transpose from any
one key into any other as fast as he can write, and
with no chance of mistake. Write down in a row,
distinctly, and in their proper order, the names of
the twelve notes of the chromatic scale, beginning
with the keynote of the tune to be transposed:
underneath this write them all over again, but
begin this time with the new keynote. Look in
the upper row for the note to be transposed, and
underneath will be found what it must be written
in the new key. Thus, to transpose from C to
F sharp, for instance,

C C D D E F F G G A A B
F G G A A B C C D D E F

All the notes represented on the keyboard by black
keys I have called sharps for simplicity.-JOHN

THOMSON.

[53174.]-Transposing Tunes.-Every one who wishes to transpose a tune on any musical instrument must fully comprehend the scales. If "Progress" will take the trouble to write out all the diatonic scales, both major and minor, with sharps and flats, he will acquire thorough knowledge of their construction, and learn to transpose more effectively thereby than any other means. One keynote is common to two diatonic modes, major and minor. C is the keynote of the natural diatonic major scale. Add three flats, B flat, E flat, and A flat immediately after the clef, and C major becomes C minor. A is the keynote of the natural minor diatonic mode. Add three sharps, F sharp, C sharp, and G sharp, immediately after the clef, and you will convert A major into A minor. Take any major diatonic scale, and flatten its third, sixth, and seventh degrees, and it becomes a minor. In like manner, take any minor diatonic scale, and sharpen the third, sixth, and seventh degrees, and it changes into a major diatonic scale. Having conquered this, let the student practise and play tunes written in A flat with four flats, in A natural with three sharps; and also tunes written in E with four sharps as if in E flat with three flats. Next, let him practise and play tunes in a second, a third, a fourth, &c., above or below the key in which it is actually written. If he works honestly in this order with care, he will acquire the masterly power of reading and transposing the most difficult musical composition with ease.-THOMAS BERRY.

[53195.]-Distillation of Wine.-By way of a guess I would suggest that the wine had been "plastered."-T. J.

lose power by the extra friction incurred in foring [53215.]-Engine Query.-The engine w the exhaust through the longer pipe; but would not be much. A trap must be put catch any condensed steam, and to draw of

water.-ESSAR.

[53219.]-Organ Tuner's Stiff Finger.-I querist must really show his finger to a surgeonT. K.

[53224.]-Dyeing White Coral Rock-It not know whether the white coral can be dyed the querist might easily try by steeping in ammoniacal solution of cochineal, having the coral for an instant into water made si acid by aquafortis.-NUN. DOR.

Forge. Either a

"clapper at bottom" is not all right, or the oce
[53236.] Portable
for the air is sufficiently large to permit the
the querist ought to be able to discover for hi
tents of the reservoir to escape very rapidly. T
much better than anyone can from merely readi
his query.-ESSAR.

seems to be the only method by which the que
[53237.]-Model Steering Gear.-Clot
can effect what he wants, unless he uses a g

pull the tiller over.-NON-DUBEX.

[53241.]-Robins in the Garden.-Robes no harm in the garden, but more good that he sparrow. The latter was jealous, and killed our robin.-S. R.

[53250.]-Wrought-iron Work.-As the only 3in. long, I think you might turn them dov in the lathe, taking a light cut to finish. Why a try?-AN OLD HAND.

[53252.]-Silencing Tank for Launchappliance has been described in back value see p. 412, No. 928; but it is a patent, and particulars can be obtained of the patentee.-N Dor.

[53257.]-Value of Coal.-This querist whether the amount of volatile matter is a mes of the value of coal for steam-raising purpes think not, because, if so, anthracite would be worth very little indeed. The large quantity of hydrogen, the greater the the thermal value of the coal, but hydrogen cont with oxygen produces water, whereas cart burnt to carbonic acid, which costs nothing rid of. It would be interesting if some of readers would give a rough and ready mess estimating the steam-raising value da STOKER.

[53262.]-Polishing Stone.-Probably Wat of Ayr stone.-C. M.

[53273-4.]—A and B Naphthol-To GANIC CHEMIST."-I beg to thank this gentle for his replies to above, wherein I am mended to use the sodium salts instead of but will "Organic Chemist" kindly infor how I could then separate the A and B from other in the state of naphthalene sulphonie PHENO-QUINONE.

[53343.]— Orionis.-I am obliged to "E. A for his information; but he did not quite a my inquiry as to the two small stars po wards Orionis, but which do not appear in P tor's "Atlas." Can one of them be No. th Greenwich Catalogue for 1860? Difference of - 15s. P.D. + 64.-H. K.

[53367.]-Electric Lighting by Batteris If Liverpool Tradesman" will make a battery, two carbons 7 by 3 by, and one ine 34 by coupled together, and put into jar twenty of these ought to work a 20 cp. Swan resistance lamp, excited with following solut Powdered bichromate of potash 1lb., hot wat pints, stir well for five minutes, then adha of nitric acid, stir well; then mix one pint sa acid with two pints of water, and add bichromate solution; stir well, and then more pints cold water. When the solution 2

Korscope Eyepiece. - To Ma. quack Mr. Lancaster for his my way, wirk I had began to [53211.3-To Colour Leather. Why not try spray worth. I have been from home saffron itself? Some use annatto with it. Boil the * was dr. the may, I have used cast- saffron until the dye is extracted, and when cold grading and are completed the add alcohol. The shade can be altered by adding w it act to my estafaction, and more or less oxalic acid. Apply with a cloth, and I have a few hints, and, when nearly dry rub with a woollen rag slightly MARIT ST. Is it required waxed. Fustic berries boiled in alum water give a heyen it how to eyepiece should be yellow. Picric acid and water (1 to 10) give a **** sprzmately? (2) yellow. Powdered turmeric and gamboge digested AVRAS O the ita revolve in in alcohol will yield a bright yellow dye, but the it is ready for use. I use low-resistance la but we be had in hand? leather should be first washed over with alum or Swan's, and with 16 of the above cells! tre se tua greidd sad poliated carbonate of potash solution.-NUN. DOR. first-class light. Liverpool Tradesman by babes, 400 that during the (63212.)-Boiler.—This query can be answered have one of my lamps if he will advertise ar a radius of we can we de geestes? My to which only by guessing, unless after a very elaborate cal-dress, 10 c p., 4s. ; 20 c.p., 48. 6d. I work! culation. The best way is to test the boiler by 10 c.p. with 16 cells on Saturday night Primat, was his filing quite full and heating, loading the valve to hours, giving a brilliant illumination. about twice or three times what you think the work success.-H. ROWTON. will stand. The process has been described several times. Then as to what the boiler will do, that depends very much on how the fire burns: and I think the querist will admit that it is difficult to determine that from the dimensions. All that can be sud is the boiler seems a pretty good design; but nothing save the practical test will determine its i capabilities-ESEAR.

[53367.]-Electric Lighting by Batter If a "Liverpool Tradesman" wishes to bring himself endless trouble and annoyance al disappointment, let him endeavour to window by battery power. The stumbling he has come across already are as nothing, 1 say, compared to the answers to his qu Bottone and G. D. Goold. Who ever ha

ghting by means of a Daniell battery? It is totally suitable for the purpose, and I cannot divine what Mr. S. Bottone to mention it. According to his lculation the lighting of five 20-c.p. Swan lamps r hour would cost 2s. 6d.-a nice prospect for a Liverpool Tradesman." On the other hand, G. Goold reduces this amount to 5d. per hour for the ne number of lamps. Which statement is correct? en, again, does G. D. Goold mean to assert that e 18-c.p. lamps diffuse as much light as six of ay's No. 4 burners? If not, why mislead the [53414.]-Floating Anchor.-Kemp's book on "Yacht and Boat Sailing" describes a floating arist? G. D. Goold ought to know that an 18-anchor as made of two iron bars formed into a cross, lamp does not give anything near the light of and connected at the middle where they intersect candles, and consequently five lamps are no use take the place of six burners. It is giving advice by a bolt, nut, and pin. At each end of the bars ich, if followed, can only lead to disappointment hauled taut, and well secured. Over the square disappointment to "Railway Bath," I venture to is a hole, through which a strong rope is rove, [53451.]-Rifle Query.-In order to prevent disgust. I should very much like to see the thus formed a piece of stout canvas is laced to the answer this query, although it is specially addressed alt given by 14 18-c.p. lamps when lighted by roping. Four stout ropes are made fast to the to Mr. Pearson and answered by him. cells, especially as G. D. Goold stated in a few bars to make a sort of bridle or crow-foot, the volunteer's rifle I understand the querist to mean By 18 previously, that it would require 24 cells to other ends being bent to a ring for the cable or the Snider. This weapon is quite useless for target at the six 18-c.p. lamps. If a "Liverpool hawser. To prevent the anchor sinking too far, a practice at 1,000 yards. If it were fitted with the desman" wants to ascertain for himself what buoy is made fast to one corner, with six or seven best possible vernier sights, and handled by the ting by battery power means, let him procure a fathoms of drift. A buoy rope leads inboard, as best marksman in the world, or fired from a .p. Swan lamp and use the battery he has, test it against a No. 4 Bray's burner in well as the hawser, so that the anchor can be got machine rest, it is not likely that more than 10 per ting capacity, cost, and trouble, &c., and if, up edgeways by hauling on the buoy rope. No cent. of the shots would hit the target. As for r the novelty has worn off, and he counts size is given, but I should think bars about 3 ft. making bull's-eyes at that range, "R. B." might cost, should For stowing better, I almost as well expect to hit the moon. the result not justify his long would be enough. cipations, he will not be much out of pocket, should rope the canvas separately like a sail, with ing position is not suited for any but the shortest will have gained considerable experience. In thimbles at the corners for bending it to the bars ranges.-W. WYATT. lusion, allow me to recommend for his perusal be turned parallel to each other, and so be less when required. When not in use, the bars could article on page 295, No. 976, of the "E. M.," he Cost of Primary Batteries," which I venture awkward to stow. I do not know of any book on ay will be useful.-C. D. R. internal fittings of small craft. Querist might inspect a few other vessels, and get hints from them to be altered or improved to suit his own case. The chief difficulty in these small craft is the cook-oblige me.-G. FRYER. ing. If there is to be no 66 crew, а "Russian spirit lamp is clean and effective. I have found it very handy for open boat work. A friend of mine uses a petroleum stove, and thinks it very good.

the form of a cross, and covered with canvas. The good order after two years' service. I afterwards buoy is secured by a rope of suitable length to one used an 8ft. Berthon, which travelled to India, was corner of the anchor, which is fitted with a double in constant and pretty rough use for some years, span, to which the hawser is bent. I suppose has been brought home and repaired at a cost of R. Hannen is acquainted with the drogues used in £3, and is now as good as new. She carries two the boats of the National Lifeboat Institution. I persons in a calm sea, but requires to be handled have several times seen these tested, and they are with care and respect, being very light and crank. certainly very efficacious. I can send full details of It is nearly impossible to force these light boats both the above appliances if required.--WAR. against wind and sea, and common sailors have a prejudice against them; still, in my opinion they are invaluable companions in small yachts, so long treatmeut a yacht's dingy usually receives.as they are not subjected to the abominally rough J. C. H.

3395.]-Paper Organ Pipes.-I beg to inforn Fryer that the paper pipes, if painted or varned as directed, are not more affected by changes emperature than wood pipes; whilst they will d more rough usage than either wood or metal.

..WICKS.

3422.]-Splitting in Deals-to Prevent.-J. BROWN, Belfast.
sited for a reply to this query hoping to gain a [53444.]-Floating Anchor.--The best method
information, as the question is of some in- of making a floating anchor is as shown in the
st to those who have occasion to keep a stock of accompanying diagram. Two stout iron bars are
a timber. There is one point sometimes over-placed crosswise, and securely bolted together; at
ed-viz., that in stacking it is important to the ends of the bars are the holes A B C and D,
>the strips used between the deals, or other

er, quite flush with the ends of the planks. If is neglected they are very likely to crack up to point where the strip is placed; sometimes a ince of 6in. or a foot. I have seen whitewash on the ends of stacks, but do not know with t result.-D. J. N.

3424.]-Potter's Wheel.-This is a vertical
lle in a proper frame with a wooden disc
ved on to the nose of it, on which the clay is
ked or thrown into shape. The middle of the
lle has a small pulley grooved for a rope, and
is driven from a separate wheel, generally
e of wood, like a carriage wheel, only grooved
circumference. This wheel is turned by an through which a stout rope is passed and made
adant. If fuller particulars are required, see secure. A piece of strong canvas is now laced to
name in Address Column. I don't think an the rope, and four small ropes E are made fast
teur could make the wheel to work properly.to the iron bars, the ends being secured to the ring

-POTTER.

F, to which the hawser to ride by is bent. When 3429.-L. and Y. R. Engines.-No. 40 has where it is held in position by the buoy G, to in use the anchor is allowed to sink several fathoms, coupled wheels 6ft. dia., and leading wheels which the line H is attached. When hauling in the 6in. dia.; cylinders (inside) 16in. by 24in. All anchor haul in on the line I. There are various axle bearings are inside. The engines of this other ways of making floating anchors. Thus, 8 were constructed by the company dating from ), when No. 4 was turned out to (omitting 1874) suppose during a severe gale the mast breaks, and The last 10 built have 17in. cylinders. No. the only thing, to do is, let go all the anchors all goes over the side; in that case the best, indeed, (1875) has 16in. cylinders and 5ft. 6in. coupled never mind whether they touch the bottom or not els. The weight of this class in working order-lash all the wreck together and ride to it, when bout 31 tons. No. 605 class (G. N. type), by it will form both a floating anchor and breakwater, rp, Stewart, and Co., 1876, have inside cylinders in. by 24in., and four coupled leading and driv- enabling the vessel to weather the storm in safety. wheels 5ft. 6in. dia.; weight in working order tons. Both classes have had a dome added, ced midway between the valve and the chimney. ie express engines, by Sharp, Stewart, and Co., 0-1, and Neilson and Co., 1883; cylinders inside inclined 17 in. by 26in., four-coupled wheels dia., weight about 42 tons working order. will find the L. and Y. passenger ines have not smaller driving wheels than other panies. If he will refer to the L. and N. W., will see smaller wheels both in passenger and ds enginess.-R. N. H.

urania

-JAMES MCCASH, Govan.

The stand

my promise at the earliest opportunity. At pre[53464.]—Orguinette.-I shall not fail to keep sent, I am quite unable to devote the necessary time required to write out the instructions for making an orguinette. If "E. D." will kindly retain his patience for a little while longer, he will

[53466.]-Composition for Binding Paper.Try liquid marine glue or coaguline.—SHUNT.

[53469.]-Exhaust Injector.-The steam and delivery nozzles are similar to Giffard's injector; the combining nozzle is split, one half being solid with the nozzle itself, the other half loose on a hinge, thereby enabling it to adjust itself to the steam and water being used. It will also work with steam direct from boiler at any pressure. A paper was read on this injector before the Manchester Association of Foremen and Draughtsmen in the Engineering Trades. A copy could no doubt be had by writing to Mr. Savill (the reader of the paper) at the Exhaust Injector Co., St. Ann's-square, Manchester. These injectors are doing well.-BOSWELL. [53470.]-Dissolving Prussian Blue.-I have an idea that a solution of oxalic acid will dissolve this pigment. It will only cost about a halfpenny to try.-Os.

[53470.]-Dissolving Prussian Blue.-You will find that a strong solution of oxalic acid will dissolve it at once to a dark blue solution, which can be used as you state; but the oxalic acid is very poisonous.-R. A. R. BENNETT.

[53472.1-Time.-The simple instrument known the correct time by the sun. It is described and as the meridian dial would enable "S. B." to get illustrated by Sir Edmund Beckett in his "Treatise by me, and will describe it if Editor would spare on Clocks, Watches, and Bells." I have the work the space.-C. E. WESTALL.

[53472.]-Time.-"S. B." can obtain the correct time from the sun by noting the exact instant that or subtracting the figure for the day given in the "Phoebus" crosses the meridian, and then adding "clock before or after sun" column of a reliable almanac. To find the meridian accurately, see answer 53506. An instrument which might meet "S. B.'s" requirements is described and figured in No. 364 of the ENGLISH MECHANIC; there is also of which I remember seeing.—ARTHUR MEE. an arrangement called a dipleidoscope, a description

[53448.]-Harmonium.-The harshness of tone may be subdued in various ways. 1. By placing one or two layers of wadding immediately over the [53473.]-How to Get Fat.-In reply to pallet-holes. This will not improve the tone, but Skeleton," I may say an authority has informed merely smother some of the harshness. 2. By me that there is no royal road to "expansion"; in reducing the size of pallet-holes, but this operation fact, no guaranteed road at all. Besides, getting is rather a troublesome job. 3. By voicing the fat isn't the thing-it is getting strong; and a reeds, which requires skill. This is the most "skeleton " can scarcely be strong, unless we effectual method to adopt. Some of the harshness include the individual with the hour-glass and of tone may be subdued by bending the tips of the scythe. "Skeleton" might find a moderate inreeds slightly. American organ reeds are not dulgence in beer beneficial, and by way of an 53442.]-Hopf Violins.-A slight but mis- the harmonium. To effect the best tone from such steel. Take the stuff twice a day, say a dozen suitable or adapted for a pressure bellows, as in excellent tonic, I would recommend him tincture of ling error has occurred in the heading of this reeds is to place them in cells or tubes, and the drops at a time in a little water, only not shortly ry. It should be Hopf, not Kopf, violins.-wind must be sucked through them; and to pro- before or after tea or coffee. The use of plenty of duce a really good organ tone the reeds have to be cold water "all over," followed by vigorous thinned down and skilfully voiced. Better ex-rubbing, is highly beneficial.-ARTHUR MEE. change it for a small American organ, as the tone of harmoniums does not appear to satisfy you. American organ suction-reeds, whether voiced or in the rough, are not in any way suitable for your

FRYER.

harmonium.-G. FRYER.

53442.]-Kopf Violins. I regret being at
sent unable to give the information required by
Fryer, as I am personally unacquainted with
violins named. I will, however, endeavour to
a reliable opinion on them, and if successful,
write again next week.-WAR.
3444.]-Floating Anchor. R. Hannen [53449.]-Berthon.-I used a Berthon of about
⚫find a full description of a floating 10ft. as dingy to a nine-ton boat for about two
mor in the "Yacht Sailor," by "Vander-years, and found it exceedingly convenient and
cen." Briefly it consists of two iron useful, being handy to stow and sufficiently able to
nearly equal in length to the beam land three persons in moderate weather. I often
he vessel, riveted in the centre, so that they used her (sailing) for mackerel fishing. I did not
work easily on the rivet, secured by swifters in allow my sailors to use her, and she was quite in

letter, which appeared in the Evening Standard on [53473.]-How to Get Fat.-The following April 18th, will, I think, supply the information how to keep thin:-"An M.D. indorses the statements of Light, late Heavy Weight':-When a student in St. George's Hospital, I tried some experiments on my own person. I found that the quantity or quality of what I ate made but little weight-change, but on restricting the quantity I drank, a difference was soon apparent. I lost 131b. in a fortnight, and was all the stronger and better for the loss. I took one cup of coffee for breakfast,

them (not of their make) with which, and the
screw-guides, I cut all I want of those particular
threads. I have, of course, tackle for other threads
not in question, and the change-wheels supply me
with aliquot pitches when necessary. If I were
going to the Colonies to-morrow, I should want
no further equipment.
T. W. Boord.

THE MAGIC-LANTERN AT HOME.

the exhibitor himself, but chiefly in suggesting house, and then he will be sure of the result, at
subjects. The children, left to themselves, will do least as to striæ.
the rest. The cycloidotrope, of course, interests
those of the family who have artistic or mathe-
matical tastes, and an eidotrope (home-made) falls
in with their views as well.

families.

H. P. H.

PLATE-GLASS FOR OPTICAL PUR-
POSES.

"Orderic Vital" very properly says, "Hence the appearance at the focus must be a compound result. I will explain, for the benefit of any who may wish to test for themselves, the component Being an amateur photographer, our lantern parts of this "compound result." I will explain views occasionally are varied in a way open to all them in the order of their importance:-First, as like-minded men, at a cost so small that it may be to the substance of the glass, we have striæ, and [22635.]-MR. LEWIS WRIGHT has shown, in disregarded. If I chance to get a day out, say to unequal refractive power of a more general character some celebrated ruins or place of note, and have in various parts, shading more gradually into one these pages and elsewhere, how easily the magic- been lucky enough to secure, say, a dozen quarter- another; second, as to the surface of the glass, we lantern may be taken out of the region of mere toydom, made an instrument of scientific research, plate views, the first thing I do after the negatives have grooves and a more general want of perfect and the means of demonstrating scientific facts and are dry, is to make a lantern transparency from flatness-a want of optical flatness, as it is called. A 3 by As to the strim, their appearance is so manifest theories to others. As one of the many readers of them. The method is a very simple one. this paper who play at science, I here tender him 3 gelatino-bromide plate is exposed behind the that it obliterates the appearance of unequal remy sincere and hearty thanks for the publication-negative to the light of a good gas-lamp for from fractive power of a more general character; and first by the kindness of the Editor in these columns, require (6sec. is the rule for a good negative). De- that part of the glass is condemned and worth3 to 30 seconds, as the density of the negative may where striae are seen, one instinctively feels that and after in a more convenient and complete form velop with ferrous oxalate, to which a little chloride less. And since I have never found a piece of plate -those marvellously interesting and able papers of ammonium may be added (three drops of 10 per glass large enough to make a 4in. dialyte, or other on Optics with the Lantern,' which made and mark an era for all lanternists. In this short note well, immerse in alum solution made slightly acid warn the amateur against its use, and I can assure cent. solution to the loz. of developer), fix, wash object glass, free from striæ, I felt constrained to I do not presume to tread on his ground; but it has with hydrochloric acid, wash dry, and mount behind him I have not exaggerated their appearance or occurred to me that the lantern may, like the a piece of good clean glass, and the thing is done. detrimental effect? And how can he be sure they microscope, and most other things, be treated The day's views exhibited on a lantern night, with are not as numerous as in the piece I was so careful in many ways. A very large, but I hope a decreasing, number of people a description of the day's trips, or the results of to get, and in which no defect could be seen with who own magic-lanterns use them entirely for the purpose of two or three days' trips worked in together, will be the naked eye without testing? These striae are so throwing pictures on the screen for the interest and found to be interesting to most well-regulated powerful in their effect that they are seen through all the other three defects, even if they are all three amusement of what may be inaccurately called an The lantern evenings may be diversified in endless present. They are more powerful than all the other "audience," varying in number from the half-ways by microscopical photographs, chemical, and three put together; therefore, if we should condemn dozen of the family circle to the few scores at a other experiments, such as will readily suggest a piece of plate glass that had the second defect school treat or village gathering. The pictures are themselves to the scientifically disposed; but such viz., unequal refractive power of a more general shown with little comment beyond the announcement of the fact that the picture on the screen is, evenings might savour of the educational, and so character-surely, the presence of striae ought to fall into disrepute. condemn it without hesitation. Therefore, what I say, a photograph of the Arch of Constantine at want to see before I recommend amateurs or the Rome, and the next is a picture of the Colosseum in trade to try to use plate glass, for object glasses the same city. Others, happily, go a stage further and give some little sketch of the history, &c., of especially, is a piece 4in. square free from strime the places of which pictures are shown. I have then we can profitably go on to test for unequal done both these things myself, and, of course, know [22636.]-I ASSURE "Orderic Vital" (22547) refraction of a more general character, and to do that the latter procedure is the best, and the only that I appreciate fully his desire to be able to this we should have to have the surfaces optically one of the two worth following. So long as the believe plate-glass is fit for ordinary, if not for perfect. But my own firm conviction, the result exhibitor has a different audience or a different set extraordinary, optical purposes, because he wishes of much thought on the way plate glass is made, is, of slides each night, he will get along fairly well the amateur to be able to get at as cheap a rate as that if there are no striæ, there would be little or following either line of practice. But lately I have had possible glass for his work. I once thought that no general unequal refractive power in a 4in. to rely a good deal upon my lantern as the source of plate-glass would do; but my experiments have square piece of glass, or at least not enough to amusement for a small family, one of whom was compelled me, against my will, to give up all hope perceptibly affect the image formed; therefore, the seriously ill, but capable of the keenest enjoyment of getting it sufficiently free from strim to be safe to absence of striae would cause me to venture on the of anything pretty, and more particularly of use. I have, for the purpose of studying the sub- use, or recommend the use, of a piece of plate-glass views of the world outside. It being prac-ject, been over two plate-glass manufactories, and for optical purposes. Of course, if we were going tically impossible to get up a fresh series seen the whole process of its manufacture, from its to make an object glass lft. or 2ft. in diameter, it of views for what became a weekly lantern melting to its polishing. I have got from these would give more area for unequal refraction, but meeting, I cast about to devise some means by works the best specimens I could choose with my would at the same time pay for a more careful exwhich the same views could be worked over and naked eyes. I have brought them home and tested amination, even to the getting the surfaces optically over again. The plan adopted has proved so suc- them, and, as I said before, never found a piece flat, and then any part of unequal refractive power cessful that I am tempted to ask you to allow me free from striæ. I then inquired of "Prismatique,' would show itself by a local alteration of the to bring it before your readers, in the hope that it who knows all the materials used by the trade, he shadings of the speculum, as seen at the centre of may chance to be useful to some of them, premising having been connected with the trade practically that the junior members of my family range in for about 30 years, and having worked in some of age from three years to 14 years, and that they the best shops during that time. He told me what enter heart and soul into the plans, and will pro- plate-glass was considered by the trade, or rather ceed. The slides at our disposal are about 200, in the best in the trade, to be the freest from impersets of 50, with one of Mr. Pumphrey's admirable fections. I sent for a piece, as I described in my cycloidotropes in addition. last, and tested it with the result I there made The first night with a new set, we run them known. I felt then I could do no more than wish through the lantern, merely mentioning the title of amateurs and those in the trade to make use of me the picture, and allowing a little time for a sight to test any piece of plate-glass they may think of each. The next time I show them with a brief good; I then should get more experience, and thus general description of each, stating, when possible, ascertain if plate-glass from any maker was fit for where further information can be obtained. Then optical purposes. When I find this maker out I the audience is informed that the next exhibition will let all know soon; but from my past experiof those slides will take place on a certain date, ments, and from the letter I quoted from in my and everyone will be expected to say something last, I have given up all hope. I believe it is imabout some one picture or another. A list of the possible from the very way plate-glass is made, and pictures is drawn up and placed at the service of plate-glass manufacturers do not pretend to make all. The success of this scheme surprised me; plate-glass fit for even ordinary optical purposes. little eight-years-old had searched her very elemen-Orderic Vital" asks, do I "mean to exclude it tary geographical books for information as to places entirely from the optician's workshop? I answer, of plate-glass, and often found these grooves most and peoples, and 66 spoke up for herself" decidedly I would for all refractive purposes, until in a very creditable fashion, and fourteen tested and found fit for the purpose intended. I years gave, in some cases, information which have often thought when I have been testing a piece was valuable to his seniors. The four sets of plate-glass and meditating on a part, perhaps having been run through in this triple manner, in the size of a shilling, where two or three stria and out with each other, the entertainment took a crossed, and formed a knot as it were, how unfit new form. Intimation was made that the next such a part must be even for an eyepiece lens, and evening would be a poetical reading night. Each the optician who cuts out of a piece of plate-glass his member of the family would be expected to read pieces to form eyepiece lenses, must often put such some short poem illustrative of some picture in our a piece to form a lens, and then it goes into the eyecollection. They could choose any odd picture from piece in time, and then the purchaser cannot make a set, and the poetry might illustrate or describe out how it is that this eyepiece will not define quite the place or some incident occurring in it. A good so well as another eyepiece. This complaint I have deal of latitude was allowed, and great interest was had from several amateurs, with inquiries as to what taken in the scheme. As illustrative of its working could be the cause, for it 'seems as well made, and was visible; but with a piece of plate-glass cut the following specimens may be given. Cologne the lenses as good, both as to surface and polish, as Cathedral, 600 years in building, very beautiful, another eyepiece, which decidedly defines better &c. The poem read was Longfellow's "All are with the same speculum or object glass, and on the 'Belfry at Bruges,"-Long- same nights that the eyepieces are compared tofellow's " Carillon," and "Belfry at Bruges." gether. And, again, when I have seen very thick "Conway,"-Wordsworth's "We are seven. striæ, and very decided ones, I have thought-Woe "Mont Blanc, and glacier views-Coleridge's be to the lens that happens to get one of these "Hymn in Valley of Chamounix." As only across its centre! Now, the remedy is very a few pictures can be shown in one evening, simple: have the plate-glass tested before it is it is obvious that a set of two hundred views cut up, and the bad places marked and not used will serve for a considerable number of evenings of for lenses. This I offer to do for any one. There this description; and, judging from my experience, is now no excuse for anyone, either amateur or in all the members of a family will take the keenest the trade, using defective plate-glass for his lenses. interest in them. A little work must be done by It will only cost him the carriage to and from my

architects of fate." 66

curvature.

But as in a large object glass these unequal refractive parts have to be corrected by local alteration of the surface, we need only test for striæ, for which optically flat surfaces are not

needed.

make up the compound result at the centre of Now as to the defects on the surface that go to curvature-the most powerful is the presence of grooves from in. wide and upward. These are easily seen when present, and are caused by the mode of polishing adopted for plate-glass, and are apt to be near the edge of the sheet being polished, and in certain parts where the motion imparted by machinery to the polisher gives practically to that part of the polisher a straight motion, although the polisher seems to swing about. This being repeated, and not reversed by the mode of polishing adopted, cuts grooves, and this is why, principally, plateglass will not do for flats in the Newtonian telescope. I have examined by reflection the surface manifest. They can be seen likewise by the contact test, which has been described in our columns before, provided a good flat is used to test by in this way; they stand out very bold before the speculum. But so great is the power of striæ, that they are seen through all these grooves. There are some pieces of plate-glass perfectly free from these grooves, and this leads me to the last consideration

viz., the surface not being optically flat. This is the feeblest cause of defect in the test, so feeble in fact that I have never been able to detect its effect except I have been testing a piece of plate-glass whose rounded edge showed that it was the outside of the sheet from which it was cut-there its effect from the centre of the sheet, I do not think its effect would be visible, especially with a thick piece of plate, for I have found thick plate much truer i.e., nearer optically flat than thin plate. Its effect could only be seen, so feeble is it as compared with the three first defects, when these three first defects were absent, so feeble is the effect of refraction through a surface so nearly flat as a good (and thick) piece of plate-glass ought to be.

If Chance's optical plate were used for all the lenses of a telescope, the difference of first cost would be very little compared with the whole cost of the instrument, and the advantage would more than pay for the little extra outlay in the better