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Oft- perpendicular height. with a horizontal pipe of3in. going off near the top with; a descent of 3fL or so, to serve as a heat-trap. But this should be into n kitchen chimney finally, to enmre the continuous carrying off of all vapour, otherwise thia would injure the plants. It is requisite also to have an earthenware vessel on the top of the bouse, with water always in it, to ensure requisite moisture, or thia heat will be found too dry for plants. Great care must also be taken at dust, or the leaves of the plant* soon become covered from the cleaning out of the stove.

There Is also an Item of expense In repair. Though ihe iuteri.ir of the stove, lined with fire-brick, will but for years, tbc sheet-iron P'pinjr, the chi-ape»t and easiest healed, will rrqairerenewiugevery three yean, at a cost of about 30*. to ti.

Anthracite, or malting coal, sbonld be used, with care not to supply too much air at any one time, or overheating will be ihe result. Thla system waa naed for three years with No. 170S houee, 40 £as could not be had moderate. Should anyone be desirouspcrsona/^ to inspect and test these particulars of heating by gas, ho bu gnly to apply at 21, i'ark-street, Bath.

J.B.

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TELESCOPIC-ANSWERS TO QUERIES.

Etsj—In accordance with "Leo's" request (page **!. I give him my method of roughly estimating the ngure of specula:—Procure an open wooden frame, almiiar u> that of a schoolboy a slate, across which are la be stretched parallel cords of smooth whipcord, or what ta better, violin strings, or catgut, In a similar manner 10 a harp About (. of these strings will be enough. They should not be more than Jin. apart, and must be exactly equidistant from each other. Aext stand the mirror, which is to be Inspected on tiny convenient support, with Its face opposite a window, and at a distance from it rather more than Its radiue of carvature, or twice Its focal length. Then incline the mirror slightly, until It reflects tbo image of the observer's head when standing cloao to the window. In this position then, with the face looking toward* the mirror, hold up the test frame between the eye and the mirror, and parallel to It, until the Inverted Image of the cords la seen reflected on lta sur

Fio. 1.

face. If now the mirror be spherical, the cords will appear to converge towards each other as thoy approach the edge of Its disc; but when the mirror is truly parabolic, the cords appear as they really are, perfectly straight, and equidistant from each other.

The simplicity of this test speaks for itself; and should the operator hare a Venetian blind to his window, that alone would be sufficient, without a test framo, to enable him to form a tolerably correct idea of the figure, providing tho room is large enough to permit tho mirror being placed at a sufficient distance.

1 should say that to give this te*t its best trial, the eye should be brought as uear to the mirror as distinct vision will permit. An. distortion of the parallel cords will then be exaggerated just In proportion as the lines are magnified; and it preferable, the cords may be only Jin. apart to bear this amplification.

Next In order, I must attend to my " Pupil" (page 500), or else ho will think me by this time a forgetful teacher. "Pupil " seems to think " the band suspension tho best for such as himself, with blanket to rest

on." I should think so too. Ho will no doubt find rt very comfortable, and will do r r betur to rest 011 the blanket himself than trust his mirror there. Blaukets are very nice things in their place, but I, for one, have no faith in them as supports for specula (unless, perhaps, when they are small). Uo should try the method explalued on page 601; It will answer perfectly for a loin, glass, or even larger. The plane for a lOin should not be less than Ilia.; 21b. Is still better. As to the ordinary plute, I have nsod a flat cut out of this material for solar observation, and it has shown the rice grain stippling very plaiuly; but I have not yet tried it on tho stars, but bellevo it would work well. I may add ihat the cone of rays In a Newtonian, although bent or diverted to an angle <-f 45°, suffers no other alteration beyond a slight diminution of light; the object seon Is in the same position, and moves across the field in the same direction, with respect to the observer, as in n refractor.

The foregoing replies will no doubt satisfy 'G. O., on the same page. My mirrors are made of lln. gluts. I do not consider myself accomplished in the art of silvering glass, although I have produced some very decent films. No doubt scrupulous attention is required to the directions given by Browning, who, I may say, has kindly informed me that the temperature of the room ha» much to do with the success of it. It should be not lese than 70°, and great care must be taken to get the glase perfectly clean. 1 have found that after cleaning the glass wiLh nitric acid, an alkaline solution is useful belore the final washing with water.

As to the question askod by "Novice," раке 606, 1 am sorry to say I am at aloes to kaow what he means. 1 am afraid he is running his head against some imaginary post. Let him read the directions again more -carefully. • W. Puhkibs.

ELECTRIC MACHINES.

Sir,—" Derf Errao," page 657, reminds me of a promise of information as to Carre's improvements in ■electrical machines on the inductive principle. I havo not happened to meet with further particulars than those ho gave or referred to, and they are by no means clear and comprehensible; and I have had too much on my hands to make experiments, especially aa I feel very doubtful if the matter is of much value. If " D. E. has not the number, he should obtain No. 220, which contains a description of Holtz's machine, on similar principles. I have tried vainly to get a eight of one, but none of the Instrument makers appear to think them worth troubliug themselves about. In reference to the brown paper machine, I do not think my remark was calculated to raise the ■querist's hopee unduly, aud I quite agree with *' D E." in what he says, it would be a very poor investment of time and labour. I expect a great drawback would be the hygroscopic nature of the paper, which is not а very good non-conduetor is consequence. As to the ■ebonite disc, I hope '' D. E." will get off better tham I did. I ordered a 15in. one, and was charged 17s. ßd for it, though weighing barely 21b., the seller declaring he had to get it from Germany. Flat sheet ebonite, say !in. thick, can be got and cut to size without difficulty, and the price is about He. Od. per lb., while the ■cuttings from the square would be valuable for making up other instruments. For an induction machine a much smaller plate would do; and as there is no strain on it, only sufficient thickness is needed for maintainingits form. Ьшыл.

HORIZONTAL WINDMILL.

Sir,—Seeing that the subject of windmills is being ventilated in your paper, I send you drawings of a horizontal windmill which I have designed, and which may perhaps be useful to some of y»ur readers. Fig. 1 is a horizontal view, and Fig. 2 a view of it as seen from above. The letters are the same in both figures. The sails as shown at A, Fig. 1. arc fixed loosely on to the levers, so as to permit the upper half to fall forward until bor i sonta 1, as shown at A1, when the lever itself keeps It from further depression; neither cau it go farther back than a perpendicular position. The sails are not fixed on the levers exactly in the middle, hut, as shown at A, Fig. 1. the upper half is lnrger than the lower. В is n pulley "fixed on near the end of each of the levers, round which a cord runs which is fastened to the top of the larger halves of each of Ни; opposite sails. Fig. 2

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«hows the position and working- oí tho sails when in operation, tho wind blowing in the direction indicnied by the arrows. At A1 tho wind has the greatest power, the sail being in a vertical position. Soon niter passing A' the last pressure of wind on the sail will cause the »pper half to full backward at the same time by means of the cord fetching up the sail at A« to a vertical position, the wind itself forcing It up Immediately 11 is raised above a level; tho opposiie sailor the wlud Indicated as A2 being then hi the

Çosltion shown at A^, the wind has no power at all. he levers can be shortened to suit the power of the wind, as the luncr part, beiughollow, permits the outer to be pushed into them and fastened with a pin at С I havo made ene similar to this on a small scale which works admirably. 1 think great power couJd be obtained by this machine. Next week, with your permission, I will send you drawings of another windmill, by which I Ihink still greater power could bo obtained, aud which would be admirably adapted for working ship's pumps, as on board ship there is

frenerally plenty of wind at man's disposal, bot which s seldom made to perform thoso duties besides propulsion, which would be the saving of trouble and ■expense to the owner.

A Hdstic гном Berkshire Downs.

HORIZONTAL WINDMILL.

Sin,—In reply to " P. I'." and Mr. J. Thrower, I beg tosíate that I should regulate the machine in the following manner :—In the first place, I should weight the cord Л (Flg. 1), which would run over the pullevwheel C—with tho

A

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weight It, tho lal

ter being light

enough to allow of

the sail swinging

out in a high wind,

as in A, Fig. 2, and

thus permitting the

excess of wind force

to pass by. Secondly, I should cause the red D F, Fig. 1, to pivot

at E, E being above tho middle point of Ü F, and К F consequently longer than D K. The effect of this would be, that when the sail was ator about В (Flg. 2), E F would swing back aud D К forward, aud the whole sail He more or less edgeways to the wind, as in Fig. 3. To prevout this occurring, however, in any but heavy gales or strong gusts of wind, I Bhould weight It at G G, and also perhaps have a cord running from G to К and M (Flg. к 2), with a weight attached to

It as before. A better, but more expensive plan for regulating

the sails at В (Fig. 21 would of course be to have them

made with movable weighted lane, as in tho ordinary

"patent sails" of vertical

mills. They would then

open in a high wind at B,

close at A on the reverse

side of the sail being presented to the wind, and thus

cause the cord and weight

Fig. 1, to come into play.
Tho sails might slip up and down the arms, as this

would admit of the leverage being lessened or increased

at pleasure. In such a case they must pivot on a

tube. If the arms were not very heavy, they might

be shortened, if required, by being drawn through the

shaft, thus:

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Head of Screw or Peg to fasten the Arm to the Shajt.

I cannot answer Mr. Thrower's question as to the power required for his lathe. If Mr. T. makes any experiments, and would slate the results in your paper, I ehould be much obliged.

/ have never tested the above plan, nor indeed any other. 3Iy model has no regulator. II. Alcak.

P.S.—Instead of cords aud weights, steel eprings might be used to catch the sails. The springe should of course be strong enough to resist an ordinary wind, and w.-ak enough to yield to a g*le. The sails should be much larger than I havo re- ¡J Arm

pr;>ented them either in this or my former letter. If there were four sails, ono cord only would be In tension at or about A, Fig 2 at any one time. If there were eight sails, two weights would he needed, and cords 1, :i, 6 7 must bo tie! to weight No. 1, the others i., weight No. 2

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Sin,—My reply to Mr. Thrower and "P. P." was forwarded to your address before the number of the Esulish Mechanic containing Mr. Yallanccs letter reached me.

I must apologise If I have at all infringed Mr. Vallance's patent, but nt present do not understand very exactly how fur our plans agree Would Mr V kindly send a side view of his mill, with sails and spring rendy lor action?

I have never made any use of mine except as a motive power to a smnll mode! raft fitted-with paddlo wheel». I thought it possibly might be employed to force a vessel against the wind. Clumsiness of workmanship, however, and disproportion between «ails and paddle-wheels prevented my arriving at any decided opinion on the subject.

1 have known my mill revolve with onlv ono sail up but faucy it would do so ouly lu a high wind, my model being too small and ill-made to admit of much momentum. H. Aloau.

"F.K.A.S." AND ТПЕ NAUTICAL ALMANAC.

Sir,—In answer to a query from " Kquatoreal," concerning tho tables of Jupiter's satellites, that appear in the "Nautical Almanac," "F.K.A.S." has employed language which, I thiuk, is susceptible of misconstruction, as it may bo thought to censnre the authorities tbat publish the "National Ephemeris."

The business of the computers of the "Nautical Almanac," is to accurately deduce certain results from certain tables, and the predictions concerning the phenomena of Jupiter's satellites, ate in this respect as accurate as any other part of the work. 1 will remind •' F.K. A.S.," that the use of au ephemeris Is not only to ouablc astronomers to observe certain phenomena, but to enable them to make comparisons be-, tweeu the assumed theory a>d the observed fact, aud so to derive the nmountol correction that must be applied to the elements, to bring the theory in accordance with the observations; and when the elements of Jupiter's Batcllitee come to be re-discussed, the discordances between the predictions and the observavations, will be of tho greatest use, and the accuracy

with which the predictions have been made, from an assumed theory, so far from being the approbiium of t»u Nautical Almanac," may be its prldef

"F.K.A.S." says, that the иве of Damolseau's tablee ought long since to have been discontinued, but kiows that there are none to replace them ..nu surely ciinmot be an insinuation that the " Nautical Almanac office ought to have computed other», that should better represent the observed phenomenal It is the duty of computers attached to that establieament to use, and not to form tables. W. E. P.

THE RELATION OF POWEE TO APERTUKKS IN TELESCOPES.-TO "HUGO." Sib,—Willi roference to this subject, I do not think the explanation of "F.K.A.S." satisfactory, it la evident, that if the magnifying power of a telescope, еачепв paribus, be doubled, the image of the object on the retina will then oceupy au area four times as great, and consequently the intensity of the light must be reduced to one-fourth ; therefore an object gloss oí faur times the nrea would be required, i.e. of twice the diameter. From this it will be understood that the power to be need must vary directly as the aperture, and not as the area of object-glass, as "Hugo"

supposes. S. X. РВЕ8ГО*.

VIOLIN TAUNISH.

Sin,—A week or two ago a letter appeared In the Enc.lisii Mechanic, signed "В.," inviting discussion on the subject of violin varnish ¡ but although it appears tornea Bubjecteminently worthv ol attention, and of interest to a considerable number of your readers, " B.'s" Utter has not at present elicited any rüp yV. venture to «г"0 this letter in the hope that the subject may be re-opened by attracting tho attention of somo of your chemical subscribers or other«, although they may not themselves bo directly luterested In the construction of the violin.

The requirements of a good violin varnish are, that it should afford protection to the wood, but at the same time it must not interfere with the vibration of the instrument. All the ordinary varnishes made from gums and resins arc quite unsuitable for violins since they do not allow the wood to vibrate freely ML. Grivel, who professes to have re-dlscovercd the Old tremona varnish, says that not one of the eubBtaices used in ordinary varnish is used in compounding it, and that it is a spirit varnish. If this latter assertion Is true, it upsots the generally received opinion that the Cicnion« makers varnished in oil.

There are many who insist that the sole cause oí the superiority of the Cremona instruments is the varnish with which they are covered; but although no one who has studied the subject properly will hold this idea, no one will deuy that tho Yarnlsh is of very greot Importance; and any hints in the Mi.cii.vnic would be highly Interesting to many.

la conclusion, 1 innv suggest a method by which the fitness of a varnish for musical purposes could be tested. Two thlu slips of the same wood, and of the same dimensions, if made to vibrate in the same manner—that is, made to produce the same nodal division—will render the same sound. New, if one of two euch rods he covered with the varnish under examination, and then both rods be caused to vibrate again, the effect of the varnish will bo at once apparent. II the varnish bo bad, the covered rod will give a lower sound than before ; but if a varulsh could be forrad that could be applied to the wood without lowering the sound, or, in other words, without interfering with freo vibration, tho desired result would be obtained. J. T.

HOW TO MAKE AN ERECT DECLINING SUNDIAL.

Sir,—I am not about to repeat in this letter what яав been offered in a former one, and for those who wish to know what an erect declining sundial is, I will refer them to No. 252 of tho English Mechanic. pago Mn. My object now is to state the method of constructing' such a dial by the terrestrial globe, which may be of service to those who prefer dolug it this way to working it out by trigonometry and logarithms. All sundials, whatever be the declination of the place, may be made upon tho principle of a horizontal dial, 11 we only know the latitude and longitude of the place to which the declination of the plane answers, for all are constructed for the meridian of Borne particular country; aud in declining dials, the reason of the substiler line being at a certain distance from our 12 o'clock line is, because tho country where it would be a horizontal dial has the time earlier or later, according to the declination of the plane. Thus, for instance, we nil know that the time in Africa is Inter than in Loudon j that when it is Ihr. lcmiln. at the Cape of Good Hope it is 12 o'clock at London; consequently the sun will come to the meridian of any place in that country sooner than hero. Suppose the plaue on which we construct our dial decline from the N. towards tho E. 63°, we shall find by the globe that such a place corresponds to a place near the S. coast of Africa. We must first coun t B0° from that point on the wooden horizon, which will be 27° from the S. towards the В., and having made a mark on the globe where it touches this point on the wooden horizon, we must bring it to the brazen meridian, and then wo shall find Its latitude and longitude. We must remember, however, to have the pole elevated to the latitude 51° 3C, and the meridian of Greenwich under the brazeu meridian. Wo shall then find the latitude to bo 3:,<Ч1У S , and the longitude 33° E. The difference of time, therefore, is 2hr. 12min. ; but as it would be very Inconvenient to subtract this amount Irom our dial, we can arrange the hours for the latitude of Loudou In the following way : Keeping to» gloto elevated, tve may pass a thlu etrip of bras» across it graduated to 18u°, or a thlu tapo woàlï answer the purpose—one end of It must be placod on the wooden horizon exactly at the degree of the wall's declination. Thus, we must bring one cud of it to (H° from the N. towards the E. ; we must then pass It under the brazen meridian across the zenith, which aa the globe Is elevated, will be Щ" from the Pole'

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90* distant from (be point of declination; and as it li

impracticable to mark every meridian on n terrestrial

globe, wemsv, for convenience, take that of Greenwich,

and torn the globe until it toaobea W from the K.

point towards the .S., then it will be Uo° distant from

the point of declination, and so a right angle will be

formed j then in the point where it cuts the tape, or

thin strip of brass we shall tind both the things

require). The number of degrees on this meridian

(which may be measured by the quadrtnti reckoning

from the ■. Pole to the part where it cuts the tape, is

the elevation of the style, which will be found equal

to the latitude 33* 40\ and the number of decrees on

tie tape or sttip of brass, reckotiing from Ihe zenith

tntke part where it cuts the meridian, will he the

distance of the aubatiler line from ihe l'-t o'clock line,

tamely. l'i= 45', over which the style must be erected

perpendicularly.

A san-dial of this kind I mado soma time aeo on the wall of a bouse, working it out first by the globe, and tkea -verifying the results by Ue formula in trigonometry, and it snsweredJ.tbe purpose admirably. It ia a m< st useful kind ol dial, and Is often to be met with. The hour-arcs may also be found by the following- formula:—H: Cob A. C: : ten. A I Cot. A CD. .-.BCD fs known; then again, cos Ji C D: cos A I'

D: : [an AC: tan. Ji C, which will give the morning hours; bat for the afternoon hours we roust make the angle A C B, SO" + 90=, which, worked out by logarithms, will give the distances required. I hope. Sir. to finish these remarks on dialling in one more letter. T. S. H.

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TURNING BUNGS WITH A FOOT LATTIE

Sir,—I bought a small foot lathe about a month

ago tor the sole purpose of turning bungs. The size

of It is 3J' centre, with a 2' V fly wheel. I have

spent a considerable amount of time in trying to lind

out a plan by which I could them ithe bungs)speedily,

and tried three or four dili-rcnt ways without, I may

say, any success. I have ne doubt there is a proper

method, if I only knew of it. by which I could turn

them with great speed, and fear I am only csposlng

my want of mechanical skill lu asking a question

whic-h I have no doubt is simple enough to the

initiated- I shall be very thankful if you or any of

the readers of your valuable journal can tell me of a

good plan or instrument by which 1 can accomplish

my object. P. Kcssv.

TURRET CLOCK.

Sib,—Will yoo kindly allow me to ask Sidney Maddison If ho will explain the manner in which the hour and quarter trains of, his clock are discharged, and also to explain the winding more fully, and how the motion work is worked. Can the clock be seen in action ; if so, where and at what time?

Compensation.

POISONOUS POSTAGE STAMPS.

Sir,—I went to see a friend of mine one night last

week, and, much to my surprise, fouud him suffering

from severe vomiting, as he seemed quite well when I

saw him at noon of tile same day. 1 risked tho cause

of his skki.es>, and he informed mo that ho had been

despatches a quantity of circulars by post that

evening, and that the gum—or, better, the '■ glutinous

concoction '—oil the back of the penny stamps had

marie him. rurj tick. i\u« is not this too bud 7 It

almost mattes one shudder to think what this stuff is

composed ol; and we know for certain that some of

ft mntt pass down the throats of stamp users. There

are many "pretty, palrnt" littlu devices lor wetting

postage stamps, but how mnuy uso them? We can

safely say that Sfl out of every 10;' stamp*consumed

In the kingdom ure wetted with the mouih. The

higher priced labels aro: free from this concoction;

*>also are the stamps ol tho Inland Revenue Deparl

nent. What excuse has the Postmaster-General lor

litis?—surely not expense, seeing how small the pro

portionate cost of better gum would be, and how large his proOti are! Ono million and r. half is the average amount netted by the Postmaster-General annually . Oue would thlok ihat out ofShl* a trttlo might he found to pay for a better quality of gum- '"°lie that a change for the better will soon be effected.

Terset Denroy, I.ivrrpool. [No doubt a letter or two iiddtcseed to the Postmaster-General would be the means of putting tho matler right—En. K. II.J

THE "MACCLESFIELD" VELOCIPEDE.

Sin —This machine was made from my own design by a e'oachbuilder of the same name. It cost me £7.

Its trial trip was au utter failure. The machine; went beautifully up the street, but the driving wheel refused to bite on the road. When that difficulty was overcome, I found It hard work t» get up nlll-anollier alteration was suggested. The machine is bcautirully hlllltnatl. and v- h.eipedo riding becomes a pleasure (without toll). This Is tho only machine whore a large driving-wheel can bo used with any degree of comfort. A ilfllu. driving-wheel gives 586 pulls of the lever to the mile ; 4*ln. lakes 440 pulls; and a COIn. 354 pulls; weight about 851b., which would bo no mntcrlal consideration when one-third the movements an MM betwixt using a ,16in. driving-wheel and a 60ln. Price ought not to be more thau 8 guineas to have a durable machine. This machine works by the hand as well ■■ the feet. It needs no springs, and tho maker will not let out any on hire.

J. Stanwat, King-street, Maceleslleld.

What is wanted Is a simple yeast that will act on flour like brewers' harm, nud that can be easily made by ordinary person. good bread frtBDpOWdert or German yeast being an impossibility to'hose wbe know what bread really is. I. Estee.

Cross-bow.

Sir —A correspondcat In your paper has, through your kindness, asked Instructions and dimensions to help him In constructing a cross-bow. I enclose a drawing of one I some years back obtained of an old family iu the New Forest, where they were used to shoot deer and rooks uuttl a lata period.

A is a piece of Iron In which to place the toe of the foot whilst stringing. B li, two iron brecea.connecting this toe-rest, the steel bow and stock, aa shown la No. 2. CC, the steel bow, ljiu. iu width at top, graduating, from the bond to each extreme, to |ln., having a fork to receive the bowstring. D is a groove of smooth horn to facilitate the slide of arrow, i. i» a bone sunk in the stock of the bow, on which the trigger acts, to keep It strung. It Is of circular form, projecting aeove the stock of the bow, and Is grooved. When the trigger is looaed, this bono luruB and propels the arrow, shown at A No. 2. F are strips of

A GOOD INSTRUMENT. Sir,—"G. C." mentions my name In the Sxuoea Mechanic, as the possessor of a4Jln. Alvan Clark. and which he very justly, I think, describes as a rino instrument. I have only had the Instrument some two or three months, but have used ami tested It a good deal iu the time. It seems very perfoct In both siellar and planetary definitions. It will clearly divides Arletis. n ononis it nppears to separate, but the smallcrand dull coloured star Is a little flattened, y Andromeda- is elongated, and also S Cancri, slightly I think; but in this case I am speaking from only one ob-ervulion. Tho followlug minute stars I have seen with this glass :— The ,'.th and 6th stars lu trapezium; the 0th about three or lour times iu tho last two months; the faint companion to X Orionls, as a steady object, and with all powers ; the lStk magnitude comes to »2 Arletis on three occasions, steadily, wlih in)power; T. OrionK with nearly all powers; 15 M.itioceioiia quadruple. The email stars in Sigma, Arionls, and the 11th magnitude star, companion to A Lyra, are not -'put out" with a power of loo. although are ol course not so well seeu as with a much lower power. I have seen six specks, or craters, on the floor of Plato. Jupiter and Venus I have seen beautifully denned. I have an achromatic eye-piece, giving a power ef ah nit 500, and 1 have seen with this power Venus deliued really wouderfulle well. Japttar waDts more light, and I have generally found 220 high enough. The outline of the disc is sharp, with any lower, but with a high power there is not sufficient Illumination to show the fainter belts. I here is a peculiarity about this O G. which 1 never met with before, and that is. that tho two surface* of the crowo lens, aro worked to tho same curve, and either surface seems exactly to fit the concave flint. On trying the telescope I found the O.G. would perform wonderfully well with crown lens, turned either way, and It took mo some little time beforo I became satisfied which was tho beat position for the crown lens. I tind wiih crown lens, placed In one position, the 0. G. will not bear a ring aperture so well as in tho other position, but with the full aperture, definition is very good, and this Is the position in which the lenses were placed when I received the O. (..(second hand). My experience leaves me to prefer the reversed position of the crown Ions. _ I had an opportunity of looking through "G. C.'s," telescope, 2{ln., mentioned in the Mechanic, audi lind it gives very small star discs. 1 am an unbeliever in size of star discs, varying with aperture alone, Irrespective of the local length and figure of speculum, or curves of object glass.

W. Matthews. Hill House, Gorlcston, Yarmouth.

BSEAD MAKING. SIR,—I should feel obligee If any of your readers could give me a good recipe for the making of yeast or barm. It la sometimes difficult to get It from the brewers, even in the country —I mean iu remote places, and in Loudon you can't get it all, and if you wish to bake your own bread, you must put an willl baking powders. For my own part, I don't believe they are wholesome, and am afraid they leave an injurious deposit on the system, if long used. Resides, tho bread made In this way is not light, neither is it heavy mid (no matter what pains you may take ill mixing) it is anything but satisfactory. 1 have tried Liebig's method, llorwlck's method, hydrochloric acid, earb. ainni., carl), soda. .Vc. : but they ure really failures, anJ not equal to bread made with brewers yeast Liebl-'s mode is the best, but still the bread is not sufflcionily light. Uorwlck's powders any one can try. as they are sold at many places, and are panegyrised from day to day. I have found them Ineffectual, but for those who are not particular the following form is perhaps as good as any, anil any person can make it. for next to nothing, the cost being very trifling; Ground rice, lib.; carbonate of soda. Jib.; tartaric acid (crushed very finely), «z. lobe kept in a dry place, in a stoppered bottle, or well secured from the air. Use It like other baking powders A wrod sort of yeast is mado In Hungary from bran, and I believe tho Persians use pen-e (which are windy) for the same purpo-e. but I am ignorant of the process. Teetotal harm is made of potatoes, flour, hops, and brown sugar, quickened I think with brewers' yeast. Cobbott recommends a kind of cake, made in summer time, of rye flour, but the process, although satisfactory, is Inconvenient.

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GUN ACCIDENTS. Sir—As a humane man, you will, I am sure, Insert the following description and drawings of an invention of mine for preventing those deplorable nccidtnta resulting from the unintentional discharge ol lirearms Such accidents are almost invariably caused uy the cocks becoming caught iu hedges, bushes, etc., or by the gun belug carelessly or ignoraiitly carried at full cock, when, of course, any accidental touch on tlio trigger fires the piece, and tho result Is frequently wounds or death. 5Iy invcmlon is simple, strong, and inexpensive; can be attached to any gun-locks,, makes guns much safer, prevents wear of looks, and removes tho necessity of always bringing the guu to "half cock" before crossing hedges, walls, etc. I merely add that having no pecuniary interest n uatever li the invention, and not having patented i. .11 persons ale at liberty to uso it. A the cock, w ltd the notches HUH cut or filed on its fronted ge C is a steel catch, with a square hole through it. Intoiwun the boss or button D flta, D, imUUd boss or >.tt»n countersunk at the top to receive a • "f","f""ft" washer. It has a hole drilled through Ho a kn t a stout steel pin. upon which it, turns, and which IJ rivetled to the lock plate K la a «»« '-"'%,t" t, 0 peg, also rivetted to the lock plate to I rey.m t i catch C from going below the ov« »^{ fuoild bo ing, and to support tho cock if the trif,f,er »u

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the FHstenwftld lignites. The components of the g* at a specific gravity of 05451, ia said to be as follows

accidentally polled. FFF are screws to fasten the' cover or cap H to the lock plate. K Is an ordinary V spring. The notches on the edge of the cock need not be cut qnfte across the edge of the cock, but the face of the cock can be left unaltered, so (hat the notches may be unseen. Of course C and D may be made in one piece, if preferred. His a cap or cover made of stoat nhcct-ir >n. case-hirdened, or of thin steel. In some locks It will be necessary to place the guard in the rear instead of the front of the cock. In that case it will only be necessary to invert the guard and out the notches in the rear of the cock. To set the guard, turn the boss D towards the cock, and to throw it out of gear, turn it from It. I have severely tested my invention, and find it never fail*. One of the notches B is for full cock, another far halt cock, and the -upper one is for securing the cock in case it should be accidentally lifted. I sincerely hope that the Baines safety guard may be of service to my countrymen, and that it may be tho moans of saving human life. Henry D. Baines.

DRAWING FOR THE MILLION—No. IV.

Sir, -T. 1 to 4.—Continuation of cylinders and cones. Many figures are combinations of cylinders and cones. Draw always first tho enveloping prism, the great outlines. Generalise your exercise, put the solid in other positions: p. ex., horizontally instead of vertically, Ac.

in your pages of late. To threw some light on the controversy, I beg to send an extract from an American paper, which has recently been sent to me by a friend on the other side of the water.

An Old Subscriber. "During the last few years heating with ga«» in different ways has been introduced, and doubtless this made of heating would enjoy a far more extensive application on account of its cleanliness and simplicity, were it not for the high price of illuminating gas on the one hand, and the impracticability of generating gas on the principle of Sleman's gas generator, on n small scale, on the other hand. The supply ofa cheap article, seems, therefore, very desirable; and this object, we learn, Is about to be realised by the gas works now building at FUrstenwald, near Berlin. The can Is to be generated from lignites at FUrstenwald, about 22 miles from Berlin, and carried to the latter city by means of pipes. For this purpose there will be erected at FUrstenwald 12buildings, each 105 by 62ft., with an aggregate of 70 furnaces, each containing lOretorts. The furnaces will be provided with Sleman's regenerator. The gas, after having been freed from tar, water, Ac, by parsing through condensers, is brought to Berlin through a series of pipes, 4ft. In diameter, into which it is forced by 4 cylinder-blasts »f 7ft. 7iin diameter and 6ft. stroke. The blasts are propelled by 4 steam engines of fift. stroke, and 360 "horse power each, capable, however, of working up to 500 hor&c power. The pressure of. the

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100 00 If this composition of the gas can be regularly maintained throughout, it will answer it purpose perfectly. The experiment shows that 3000 cubic feet of the gms are equal in heating power to one ton of lignite, or onc-thlrd ton of hard coal. The price at Berlin larated at 12* cents gold per 1000 cubic fret, and tho equivalent of one ton of hard coal will cost lu Berlin 1 dol. 12J cents gold. The capacity of the works mr& calculated at 9,500,000 cubic feet per annum, or about 10$ millions per day, which it is said will cover the demand of about half the city.'*

THE -WORKING OF GRANITE IN ANCIENT TIMES.

Sir,—Granite is now commonly planed, turned ia the lathe, and polished by machinery, but it ia very questionable if it is wrought more beautifully than it was by hand In ancient times. Egypt shows example* of what patient labour can effect, but ludia, from whence it is probable Egyptian civilisation waa derived, yet possesses monuments of early human skill, which are hardly equalled by any extant examples of Egyptian art.

The famous temple of Chillambmm, in Southern India (probably at least as old as the Egyptian, pyramids), originally consisted of seven lofty walls, six ot them wiibiu the external one and each within the other, surrounding the central quadrangle. These wallB had teven gateways and twenty-eight pyramids, forming a huge cross, probably by no means the earliest example of that most universally distributed figure, for the crosses discovered in Central India by Mr. filutheran, appear to be far *nore ancient. The walls of this temple extended over a mile iu on© direction, and have never, that I know, been equalled in magnitude by any modern Christian structure.

The interior of this temple is decorated by festoons of chains, depending irom pilasters; each of these chains was wrought out of a single piece of granite, sixty feet long, the links, tweoiy in number, having been carved, intersecting ench other, and highly polished ; indeed they retain their polish to this day. Each link is thirty-two inches diameter, and I nm told, only one is broken; aud much ss I dislike the desecration of ancient monuments, I shuuld like to see a few links of the broken chain in the British. Museum, for an example to English mechanics. I cannot help thinking it rather doubtful, if our automatic granito working machinery could do much better than these people of the same Aryan race as ourselves did by hand, it is said, without steel tools— but this I beg leave to doubt—notwithstanding Mr J. Whitworth does deservedly esteem its powers m highly. Tiil Harmonious Blacksmith.

VERY REMARKABLE ANCIENT MUSICAL INSTRUMENT.

Sin,—In an ancient Peruvian huaca, or catacomb, a syrinx, or l'andeau pipe, was found, which was carved out of a solid mass of lapis ollaris. This interesting relict of an ancient and extinct civilisation (which may be as old as the representations of harps lound by Bruce in the tombs of the kiugs of Egypt, an engraving of which Is In Burnty'a " History of Music "J, is profusely ornamented with representations of what are termed Maltese crosses, a thing not very surprising when it is considered that the cross iB perhaps without exception, the most ancient and widely diffused of existing symbols, both in the Old and New worlds, for It is found throughout Europe, Asia, Africa, America, and even the iMands of the Pacific, Tonga, Vitl, and Easter Island for iustauce. This instrument is alno ornamented by other symbols, very similar to those found on Egyptian obelisks, and on some of the monoliths met with in Western Europe. An engraviug of this remarkable specimen ot Pan's pipe, is in the " Trans. Roy. Boo. Edinburgh," Vol. 20, page 121. Query, does not its ornamentation indicate (iu common with the almost identity of ancient architectural remains in India, Java, the Pacific Islands, and South America), tho intercommunication of the ancient races of mankind, which inhabited the Old and New Worlds, perhaps before Hie Pacific Ucean waa formed, or at least before n large extent of land between Asia and America was submerged?

The Harmonious Blacksmith.

U— Cone cut by two planes passing through the vertex.

V. I.—Plan and deration of a square pyramid having two sides of the ba.»is: A D and It C parallel to the vertical plane of projection. V. 2.— The same inclined Draw first the elevation; from S1 a perpendicular and from S an horizontal line will give the point St now horizontal projection of the vertex.

W. 1 aud 2,—The same exercise for a cone; the ellipse projection of the basis is limited by the rectangle A BCD. G. Quilosa.

GAS AS A FUEL.

Sin,—I see that the question of gas as a fuel lias been more than once inquired about, and written on

gas in tho pipes is intended at 10ft. water, equal to about 71b. to the square inch, since this comparatively high pressure allows of a smaller diameter of the pipes, and seems to offer a lower one In many other respects. 'J he pipes are to be made of i,iu. boiler plates, and not buried, but laid above ground, to render them at a?:y time easily accessible, aud supported in an appropriate manner by stone pillars. Under a pressure of 16ft. water, the pipes will deliver 407 cubic fret per second.

At Berlin tho gas will be Btored in 12gasometers, each 15ilt. in diameter and 40ft. high, having, therefore, a capacity of about 700,000 cubic feet. From these gasomrters the city U to besupplied. From experiments mft'ie by Dr. Zulrck, of Berlin, it seem* that a gas of good heating quality can be made from

LOCK NUT. Sir,—In our valuable paper for February 25, page 575, there is an account and drawings ofa patent lock nut for the joints of railway rails. I think it would be too expensive for rallwny work, and propose a lock nut for Joints of rails iu this form; the head of tho bolt made to fit in an oval hole, so that it will not turn, and on the inner plate a small square groove, cut across tho centre of the hole, and a cut similar in the squares of the nut, but at tho back, so that when tho nut is screwed home, any of the squares put opposite the groove In the plate, there remains a square hole for a key to drop iu, bur not to be made to fit too tight, and long enough to get hold of it to take it out at any time, so that when the plates wear, take out the key and you can either give it a quarter or half turn, whichever it requires to tighten it, so that the nut is level, then put in the small iron key, and it will remain firm until wear takes place. If too expensive for main roads, it would prove valuable for points and crossings in yards, especially for junctions. Let some of our brother correspondents give me their opinion of it. Platelayer.

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KAPPEE'S IMPROVED FIRES. Sill.—IsendyouabovcarenghsketchofMr. Rapper's Improved fires, which he ha» introduced into Chatham Dockyard, with a saving of 50 per cent. *lg. 1 U tor welding tab-.. Tb. sketch .hows the working of it. When it welded the shaft tubes for tie Glutton the tabes were 13ft long, 4ft. one end, 2ft. 81n. the other This fire is well adapted for boiler-makers, lor welding the inner tubes. Fig. 2 is more for beams nlaieB, or angle iron. It is a very valuable fire. It is .easily lighted or easily cleaned out j there is no turnioK the work on ed«e. Fig. 3 Is lor heating the arms

HINTS TO CORRESPONDENTS.— •'Scrutator " savs :—" G. Forreit (p. 638) recommends • Scrutator' to slga himself 'Sorew Loose/ or 'sorew tlghtor his ideas before he rushes into print.' The force and real application of these remarks will be seen by reading further on, where he says—'" Gttcbe Manito" is quite right In saying that the machine used for shoddy manufacture is called a "willey," or vulgarly a "devil."' Now it so happens that 'Gitche Mntiito' did not say anylbing of the kind. The expresjlon vulgarly a devil wa< my own! From this I Infer that G ForreBt did not quite uuilerstand whut he was writlug ahout; I beg, therefore to Include him wlili those to whom, Hints to Correspondents' are intended to apply. 'Gltohe Manito,' whose lotters are most fully appreciated by mo, will, I am sure, see the folly of G. Forrest 'rushing into print.' With regard to G. Quilosa's more respectful letter, I beg to remark that if, after 25 years' experience in leaching, he will luiorm me through the pages of our Mt.ctiAKic that he la not sufficiently 'up' in tho subject of Projection to detect >he erroneous teaching in the book he so strongly recommends (' Projection, by Ellis A. Davidson), I will, through the samo medium, endeavour to enlighten him, although 1 have no intention of reviewing tho work In question."

CONSUMPTION.—" Hanley states:-" I am glad to sea you take so much interest in that terrible complaint consumption. Some years ago. a relation of mine travelled amongst too Portuguese, and the country-people used the following plan for all lung diseases, In the first stage —New milk one quart, then take a Sat bar of clean iron about Hln. thick, make It a bright red colour in tho fire, then stir the milk with the iron till you have reduced the quantity by a half a pint; this is taken every morning till the patient gets better : they very seldom give drugs of

REPLIES TO QUERIES.

[1507.]—SEA VOYAGE.—Seeing that no answer appeared to this query, I extract the following from the " Annualrede laMalsonde Mello-lez-Sand," circumnavigation in 1670. Theesiabllshing of the steam boat lines between Australia and San Francisco (lSflfl), and between San Francisco and Houg Kong (1887), has completed tho circumnavigation by staam. Those two lines present but a little difference as well as to tho

?rice of passage as to the duration of tho voyage,
'rices are the iollowlng in first-class (I reduce ap-
Sroximatlvely in English currency), fr.im Paris to
larstillea £4. from Marseilles to Alexandria £M 12s.,
from Alexandria to Suez £2. from Suez to Aden £40,
from Aden to Pointe de Galle (Ceylon), £.:0. At Pointe
de Galle tho two lines separate. On the northern one
we pay from Ceylon to Hong Kong £30, from Hong
Kong to San Francisco £60, from San Francisco to
Saint Nazaire, (France), £70. on the Panama Hallway
£5, and from St. Nnzalre to Paris £2. On the south-
ern Hue from Point de Galle toSlduey £50, from Syd-
ney to Panama £60, for Panama Railway £5, from
Colon or Aspinwall to St. Nazaire £44, and from St.
Nazaire to Paris £2. The whole voyage costs :—
By Hong Kong, 1st class, £203 lis.
By Australia, „ '• ''-•'

The duration in time 1b the same.

Days
Paris to P. de Galle... 25

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P. de Galle to Sydney 24 Sydney to St. Nazaire 55

Tetal

Days. Paris to P. de Galle .. 25 P. de G. to Hong Kong 15 HongKongto S. Nazaire 64

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but If any of the readers wish It, I will be most happy to give it.

Gio. Hitaut, Franklin-road, New Brompton.

EXTRACTS FROM CORRESPONDENCE.

STARCH. — H. E. Godfrey observes:—"I was

delighted with the interest taken in the subject

* starch.' Long live ourjournal of mutual instruction!

Much good might be done among pharmaceutical

students by short notes on Materia Medicu, Botany,

and Pharmacy, Ac."

WATCH CLEANING.—" Ab-oth-Tate " writes :— "To 'Veritas,' 'Stopt,' and others. The olive oil purified with lead shavin* s is very good, but if they will puichase the best almond oil, they will rind it much better, >s it does not gum nor freeze like the *e»t purified olive oil does. Tried and found good."

THE USES OF OLD HORSE.—H. E. Godfrey, referring to a letter under this head in our last number aaya :—•' It may he Interesting to soma of the readers of the EftotiSH Mechanic who have a passion for ketchup, to be Informed that there arc establishments, in and about London, devoted especially to the preparation of genuine mushroom ketchup from old horses' livers, which are allowed to decompose for the purpose."

ALGEBRAICAL PROBLEMS.-" Pneuma" says: —"I enclose a reply to a questlou in last Mechanic lor insertion In your next number, if you think it •worth while. At the same time, are you not almost too liberal In tbe space you afford for solutions to algebraic problems, which are frequently of little general interest? Could yofl not suggest to your readers that almost every young algebraist can surely rind in hla own neighbourhood some educated persou wan would be glad to help him out of an occasional difficulty."

OS SKETCHING FROM NATURE. —" Mua" aays:—"May I make a remark or two on tho above j*pers? At line 7 from the bottom the writer says, • Iliuce it u always,' *c, *c. He should have explained that If au appearauce of height is to be giveil to a building, in the foreground especially, the perspective tnsit be attended to. For instance, in rig. 1, standing at the foot of a houBe, the perspective causes tbe line of the roof to slope as in diagram, and aa tbe writer himself states aud shows, not only the proportionate height of the house, but also its posi tion. In the same Fig. we have, un the opposite side a smaller house, hence the difference in perspective Tbe onlv method we have of showing the stupeudoui height of Buch towers as St. Peter's at Home, an. Strasbourg Cathedral Is by the perspective. Proof o' this may be seeu in a lithograph of the latter church; ■by T. M. Richardson, jun."

iron and milk on a diseased lung.

MEDICAL OPINION.—" F.R.C.S." writes " to beg to add a further remark on tho question of improvement of your journal, and I venture to do so Bolely on public grounds, it is to caution correspondeuts. both those who make and those who answer medical questions at various times. I have noticed inquiries and replies calculated to lead to great mischief; I might particularly indicate some relating to tho sight and diseases of the eye. 1 am myself the chief surgeon to one of the large eye hospitals, giving advice to upwards of 10,000 patients annually, but I would not venture to rep]y to some of the questions as propounded in your columnB."

MANGANESE BATTERY.-Mr. W. H. Stone deprecates the imperfect information which has been given since we inserted his detailed account a short time since. He says :—" The ' strong saline solution,' spoken of in the last number, is bent formed of saturated solution of Bal-ammoniac. No ' perforated shelf to hold a supply of salts ' is needed ; at least mine has been working untouched for seven months without. A'cylinderof amalgamated line open at top and bottom ' is equally needless, as a small fiat strip 2ln. broad answers any purpose, and costs much le3B. Lastly, there is no need to give 7s. or evea 6s. for each cell. A quart jar costs 6d, a Oin. porous pot 7d ,a carbon to mntch about Is., zinc about 2d., Bal-ammoniac Jib 3d,manganese about lib. 2d ; total 2s. 8d. Of course binding screws and platinum connections are expensive, but there are simple means of dispensing with both.

Total 104

By the opening of the Pacific railroad, tho Australian line comes in the second rank. The shortest route round the world Is that of San Francisco ; by this lino one csu go in 39 days from Liverpool to Ilong Kong, aud tho whole tour requires only 80 days.—Camille, D. P.

[lflSlO-LOCKS.-Therc Is a book on this subject, "Constructionof Door LockB," to be bad nf Virtue Brothers aud Co., 26, Ivy-lane, raternoster-row.— Maty.

[1729.]-RINGS OF STEAM.—Any force acting ■ udrivnly uuon the air from a centre imparts to it a rotary motion, which is not only confined to loco> s and baccy pipes. If a big gnn, on a still day bo fired, without shot, with a well greased muzzle, an enormous aud regular smoke ring will be the result— Maty.

[1708.1—VARNISH.—Mr. B. Nlcoll's address 1« Regent-crcus, Piccadilly; and bis works, No. U Arch, Lachmere-grove, Ualtcrsea.-A. M.

[1799.1-RKVEUSING ECCK.NTRIC.-I cannot do better in this instance than quote Raukiuo:- To reverse the direction of rotation of the shaft of a steam engine, the piston must bo made to come to rest and then to move the reverse way, before completing a stroke, and the ecceutiic must assunio that position relatively to the crank which is proper for working the sltdo valve when tho rotation of tho shaft is reversed. That position tor the position ot backward gear) is somewhat less than hall a circumfereuce from the position of forward gear, measured round the shaft in the direction of forward rotation. To bring the eccentric, therefore, into backward gear, it is sufficient to causo it first to slaud still while the shaft nearly finishes the first halt turu backwards, and then to accompany the shaft In its rotation In most stationary engines, aud many marine engines, those objects are effected by having the eccentric loose on tho Bhaft, and Bo counterpoised, that its ceutro of gravity shall be in the axis of tho shaft, but preveuted from turning completely round by means of two shoulders, one of which holds it in the position of forward gear, and the other in that of backward gear rare Wing taken that the motion of the loose eccentric rouud the shaft shall be lorwards to go from forward into backward gear, and backwards to go from backward into forward gear. To reverse an cn

PARAFFIN OILS.—The United States" Government has recognized the danger of the so-called paraffin oils. A general oruer promulgated by the United States War Department provides that hereafter no volatile oils will bo issued or used for illuminating purposes at mllilary posts, and all varieties of coal oil will be regardod as volatile. In general, lard oil will be supplied for issues of oil authorised for the necessary Illumination of military posts.

A RARE LENS.—The largost photographic portrait lens ever made in this country is ono of lOlln. diameter, recently completed by Rosb, and now In the 'possession ot Mr. Mayall, of Regent-street, It Is an achromatic lens of great power, and will take portraits ef any Bizc, from tho smallest miBiature up to very nearly life size. It Is made of glass of the whitest inscription, and its size admits so large a volume of lighttnatpliotographscoveriagaspaceoflOiu. by lain. may be done in eight seconds. The lens renders in the holograph nil that is seen In the optical Image, and his so truthfully that the coarseness and cxaggera• ioti belonging to large photographs taken with nlerior lenses arc altogether absent. In the open air 'roups of 15 to 20 pei sons (each face about tho size of 1 sovereign, and the whole picture 21in. by 24iu.) can ie taken with the short expusure of 10 seconds, ihe cost of manufacturing the lens was upwards of £210.

■ iie with a Ioobo eccentric, the gab is to he dlsen_ • aged from its pin and the slide valve moved by hand if necessary. When the Bhaft has made part of a turn backwards, a stop on the shaft comes against n shoulder of the eccentric causing it to assume its motion, ro-cngagiug the gab and workiug the wive as before.—Maty.

[1809.1-FKATHERS IN WOOD.-The following wliloh recently appeared in tho /ItiiWer.will answer "E R. S. ■-" In the structure of all woods used in bulidiug, there 1b, firstly, a series of vessels of woody tissue surrounding tho heart of the tree, having a t'crtical growth, and arranged in annual concentric circles; secondly, there are certain hard woody growths, called tue" medullary rays," radiatwg from the heart and consequently more or ess horizontal: these vertical aud horizontal growlhs are intimately but reouiartu plaited and iuttrtKtned together, to give strength to the trunk, and thus fa. all is regularity. Now where the branches buist through the Bioin this regular arrangement is upset, and the above-mctitionea woody vessels are disarranged, and pushed at different ancles. Wnen the tree is cut down and sawn horizontally across amongst these branches, tbese disrupted horizontal aud vertical vessels (of different colours, be it remembered) are seen cut at every conceivable angle, aud an ornamental 'leather, '"ore or less extensive, is the consequence These feathers do not exiBt at the base of tho tree, because there are no branches there to disturb the annual growths of tbe wood (minute leathers do intlecd uxist nt the terj/ heart, aud these were caused by the growth ol leaves and twigs when the tree wss a acedling or little • Feathers ' are not teen in -hal. because the

cutting)

fir is a straight-growing tree, without branchc i in the

portion of the trunk used in commerce. leathers

are seen most abuudhntly in 'pollards,'for the siple

reason that alter the top of the tree has been »"» »'. au immeuse growth of brandies is alwny si tin ted disturbing the tissues In every Imagtiia ''« ««> ■. ^ action oi the light cu the feather a ^ adds picMj to their beauly alter the wood is polished. -Uirsv.

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