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described Myers's patent reeds more than once-see No. 262. The Physharmonica "Leed with a swell," has also been described in the ENGLISH MECHANIC to be a free reed combined with a pipe.

suggestion in the way of increasing the circulation, I
hope that others, who may feel inclined, will make other
suggestions, so that we may all unite together to in-
crease the prosperity of the ENGLISH MECHANIC.
HOPEFUL.

I believe the Germans put à 2ft. pipe to a tenor C reed, but it is obvious the pipe may be shortened to [Other correspondents have expressed themselves half, to a quarter, to an eighth, or even to a sixteenth Hopeful." Mr. Grierson, who has so of that length, which would approximate to the length similarly to " of the wind channels for such a reed in the harmonium. valiantly defended the Lewis system of shorthand, We have Mr. Hermann Smith's authority for regarding says:- I always leave my ENGLISH MECHANIC on our all these wind channels as veritable pipes. I infer the office table for some time, for the benefit of my fellow shorter the pipe the greater the influence of the reed students. One of them has just become a subscriber, on the short column of air within it, and of course the and a second states that he intends to become one." less the influence of that column of air on the sound of Sea says in a letter:-"I take every opportunity of introducing to the notice of my friends as the most the reed in the way of improving its timbre. "Alexandra" asks for a trumpet stop in the har-friendly act I can do them."-ED.] monium worthy that title. I can't help her, unless she can find room in the instrument for more pipe tone (along with the reed tone) than any short wind channel can be expected to afford. In such case, we at once introduce a rank, whose wind channels are so long as to take it quite out of the harmonium family. It may be I said there is no natural line of demarcation between wind channels and pipes-but a double Creed, with a wind channel or pipe 4ft., or even 2ft. long, would rather come under the category of an organ rank, than an harmonium stop. Alexandra" would cheaply obtain much information by reading; the patents mentioned in "Harmonious Blacksmith's" reply (also intended for her) to "J. C. P. ;" in No. 277.

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Referring again to the significant fact that none of

the harmonium makers have offered the least assistance
to "Alexandra" for contrast and variety of tone, it
may be that those who have mastered the details of
mere ordinary construction fear absence of adequate
pecuniary reward, for spending time, money, and brains
in the construction of an instrument very much out of
Who can blame them while they
can sell their productions? They have their living to
get, and this takes a great deal of the poetic feeling out
of us.
W. T., Pianoforte Tuner and Repairer.

the common way.

MICROSCOPE.

[225] SIR.-Your correspondent "C. C. S.," in his reply to "Sabbas," refers to a new student's micro

REPLY TO "SUBURBAN."

[227] SIR,-"Suburban" rebukes me (in all good faith
know), for what I do as a duty, and not a pleasing one.
The readers of the ENGLISH MECHANIC have a right
to claim that those correspondents who are familiar
with a subject should not suffer erroneous statements
respecting that subject to remain uncontradicted. Per-
sonally I should care nothing though "A. Z." chose
to assert that the earth is corkscrew-shaped, or though
"B. Y." said that Jupiter is a pancake; but if they
assert the theories in the ENGLISH MECHANIC I Should
not hesitate to point out that on the whole accepted
views are preferable. It is not the shortcomings of
"A. Z.," or "B. Y.," or "C. X.," that I regard, but the
injury their mistakes may do to our journal. But is
"Suburban" serious? He speaks of "* unlucky mor-
tala" who are " in the wrong," and who happen to
assail" people, almost as if he loved them, and he will
not have them "trausfixed with an epithet" at any
Suburban's" champion-
price. Are they worthy of "
ship?

Has not our own "F.R.A.S." lashed some of these
offenders, and stingingly, too? I once called in his
aid for such a purpose, and I remember it was very
effectual indeed.
R. A. PROCTOR.

THE FLUTE AND FLUTE PLAYING.
[228] SIR,-I am an old man-a musician-and

However, it is probable that the enormous circle of readers of the ENGLISH MECHANIC embraces more than one student of science familiar with the labours of Magnan and Riccius; and, I doubt not, their kind assistance will soon remove my difficulty. Should inhowever, be not forthcoming, then, sir, you or your formation as to the above-mentioned phenomenon, readers will, perhaps, favour with an answer to the query forming the heading to this letter. altitudes, the cirrus clouds, commonly called "mare's tail," appeared to him to be distant as ever. But what I wish to know is, whether or not exhalations ascend beyond the earth's atmosphere, S..... R.

Glaisher has, I think, stated that when at the greatest

HOW LL.D.'S AND PH.D.'S ARE MADE. [230] SIR, I have been an interested reader of our valuable MECHANIC during the last twelve months, and as this is the first time I have addressed yon, I cannot but congratulate you on having such an array of talented contributors on an almost endless variety of subjects. Truly there is a national education for the working man at twopence a week! If you think a few lines of nine worthy of admission into your columns, I would reply to an Ambitions One" who is desirous of knowing how LL.D.'s are made.

An LL.D., or indeed, any degree obtained in a British university, undoubtedly confers honourable distinction on its possessor, and I would add that a foreign degree is not inferior if obtained in a fair and legitimate way (i.e. not through mere money considerations).

For some years past, however, foreign universities, particularly German ones, have for a pecuniary consideration granted LL.D., Ph.D., and other degrees for sums varying from £15 to £25, and we frequently see a plain Mr. on one day emerge a full-blown Doctor on the next. I am personally acquainted with more than one who have thus obtained diplomas. It must surely be a standing disgrace alike to both university and candidate, when the latter obtains his diploma merely through purchase.

The subject of these German Yeast degrees has lately been fully exposed in the Scholastic Register. The number for July last, contains the following remarks:"The University Degree Trade has not been thriving

Scope exhibited in the Workmen's International Exhi- in my youth used to play the flute. I have heard lately; a result that is mainly due to the exposures bition as being suitable for his requirements. I have Drouet, Nicholson (in his prime), Richardson (an old much pleasure in corroborating "C. C. S.'s" statement, friend), Pratten, (ditto), and most of the later per- agents have entirely abandoned the occupation; but

formers; and am also an amateur mechanic, and con

in favour of that detestable instrument (the flute)

which have appeared in our columns. Some of the

there are still two or three in the field. The facilities

pass a somewhat strict examination."

Having worked with the instrument I am fully convinced that it is the cheapest microscope in the English sequently an admirer of your publication; but little offered by these gentlemen are, however, now of a somemarket. The stand is made of one solid piece of brass, did I imagine that I should live to see any arguments what restricted character, as nearly every European whereby great firmness is secured; it has a spring fit only for mild curates and similar-minded indivi-university is closed to every person who is unable to object-holder, a good object-glass, the eyepiece is excellent, the rack work and fine adjustment smooth and duals. I know all about the abortion, have seen overeasy. In fact, it forms the basis of a very capital intures arranged for four flutes, and have had to accomstrument. Wishing your greatly improved journal in-pany solos performed on an instrument with eight, F. B., F.R.M.S. and heaven knows how many more keys. Also, I once heard Boehm, and after that, nothing that I have

creased success.

If the above remarks are true, and an "Ambitious One" is desirous of becoming a learned Doctor in so degrading a manner, he had better set about his business at once, ere he be too late. The authorities are wise valuable, are likely to become valueless, since it is impossible to distinguish between those purchased and those earned by laborious study. STEEL PEN.

[" F. B." stated the price of the above microscope, heard, or ever shall hear, will convince me that the apparently beginning to see that their degrees, other

which we omit for reasons given elsewhere.-ED.]

OUR SIZE AND FORM.

flute is a desirable instrument for any one to waste his
time in learning to play. I once gave an engagement
to Richardson to play at a concert, being anxious to do
him a service. On the night he sent me a notice, say-
ing that a boil in his cheek made it impossible for
him to appear. Fancy the situation-poor fellow!
Read in any old novel the description of a curate's
abode-"Over the mantelpiece, on two books was
placed his flute, &c." But, with all my prejudice,
I will say, that for the true poetic "flute-like" tone,
nothing surpasses the old German flute; and I shall be
much surprised if our facetious and learned friend, the
"H. B.," does not agree with me, at all events, in this
particular.
F. F. C.

TIONS ASCEND?

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[226] SIR,-Though I agree with the "Harmonious Blacksmith" (letter 213, p. 496), about enlarging the size and increasing the price of the ENGLISH MECHANIC, I think the plan suggested by you is by far the best, if it can be carried out. You know best. At all events the offer is both a generous and courageous one. Our facetious friend, the "Harmonious Blacksmith," suggests that the ENGLISH MECHANIC should be increased eight pages in size and one penny in price. You, sir, say you do not know what the ultimate size of the ENGLISH MECHANIC may be; and judging from the manner in which it has incorporated other periodicals of late, it would not be an easy thing to TO WHAT HEIGHT MAY CLOUDS OR EXHALAforetell. But you say distinctly that you have no idea of increasing the price, though you will increase the size eight pages if you could get three subscribers where you have but got two. Here then is, as I take it, a bona fide offer, and one that reflects great credit on the management. It is in fact a challenge, and I beg to suggest that we, the subscribers, take it up at once and heartily. I believe that our subscribers may be increased onethird with comparative ease. Not one-half, I may say one-third, of the people interested in such a publication as ours, take it in at the present time. I am just returned from a short holiday trip, and I was surprised in several instances to find persons, and just the ones to become subscribers, who knew little or nothing about the ENGLISH MECHANIC; and I have reason to believe that two or three of them, on their return home, will become subscribers. I know no better way to widen the area of our readers, than for those who are subscribers to introduce the journal to strangers during their holiday trips this time of the year. In more than one instance I left my copy at the hotel, in the smoking-room; and I was interested to see how it was looked into and enquired after. I beg to suggest that others do likewise.

Our ever obliging adviser, "F.R.A.S.," said (page 312):-"I assure you I personally recommend the ENGLISH MECHANIC right and left to every scientific friend I have, and to others, who, without claiming any title to that appellation, yet wish to know what is going on in the way of physical and mechanical discovery." If "F.R.A.S.," who takes so much trouble to enlighten us, also recommends our journal right and left," certainly we, the mass of the readers, may imitate him in one way at all events, by recommending our friends "right and left" to become subscribers.

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[229] SIR,-Searching through Shaw's "Boyle for information relative to an experiment conducted by Boyle, I happened upon a paragraph (Vol. ii., p. 454) containing a statement so incredible-at least so it appears to me, although founded on the observations of two eminent men-that I venture to claim the assistance of your readers in an endeavour to arrive at the truth. I will now proceed to quote, so far as is material, the paragraph in question. After stating that, perhaps, the atmosphere may rise to the height of some hundreds of miles, Boyle says: "Nay, exhalations may ascend much higher, if there was no mistake in that strange observation made at Toulouse, in a clear night in August, by the diligent Emanuel Magnan, who, as Ricciolus tells us, 'saw from 11 o'clock at night till 12, while the moon was under the horizon, a little lucid cloud, near the meridian, and almost in the zenith, which could be illuminated by nothing but the sun; and, therefore, must have been higher than the whole shadow of the earth. And,' says Ricciolus, the like phenomenon was observed by the great mathematician Riccius.""

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Now, beyond the short explanation contained in the paragraph above quoted, I am unable to ascertain what were the observations made by either Emanuel Magnan or Riccius; yet, I cannot but think that the observations in question must have been founded on error; since, if we suppose the cloud to have been higher than the whole shadow of the earth, then its distance from the observers considerably exceeded half a million of miles; and if, as we may suppose, the cloud was at that distance of visible sensible breadth, then it must have had an actual linear surface of thonsands of square miles. That such should have been the actual case appears to me improbable in the extreme.

HANDWRITING.

[231] SIR,-Your correspondent "W. S. A." (p. 469) appears to forget that we live in an age of railways and telegraphs, and the old fashioned stage coaches and their living prototypes have grown out of date.

As steam superseded manual labour, so quick writing beautiful form of the letters," as "W. S. A. " in a burst supersedes slow writing. The "true, correct, and of poetic feeling expresses it, belonged to the days of the "sleepy Charlies." In these modern days of "tarnation hurry," it is neither necessary nor desirable for business men to write as exquisitely and carefully as schoolmasters or professors of writing. It is not style but rapidity that is aimed at this rapidity unavoidably results very often in illegibility.

"W. S. A." alludes to writing as an "art." Now to the great majority, who use it merely as a means of conveying their thoughts to others, it is not an art. Schoolmasters and a few others have made it an art for the purpose of teaching writing, but after quitting school it is not necessary for those who do not intend to earn their bread by forming their letters in a "true, correct and beautiful style "to write like schoolboys. There is no departure from truth, and therefore there letters correctly. Modern excellence is to be able to can be no ignorance or vulgarity, in not forming the write three letters in the time formerly occupied by one. Time flies and man walks. We should not consume time unnecessarily, lest time should consume us before we are aware of having wasted our allotment.

LEX.

THE FRENCH MITRAILLEUSE. [232] SIR, The Franco-Prussian War and the part being played therein by the mitrailleuse will probably cause brother readers to welcome theannexed illustrations and description of this deadly weapon. The mitrailleuse is the patented invention of M. Francois Jules Manceaux, of Paris, a gentleman well known for his various improvements in firearms in general, the English patent having been secured through Messrs. Robertson, Brooman, & Co., patent agents, Fleet-street. A mitrailleuse was patented by M. Manceaux in 1867; the present invention, however, is a great improvement upon the former weapon. The first part of the present improvement consists in fitting the barrels between plates which stretch across from one side to the other, and are connected to side plates or straps, which are carried on

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trunnions. The trunnions enable the apparatus to b mounted upon a carriage, so that it can be used in fiel operations.

The principle of the French mitrailleuse will be seen from the accompanying engravings, fig. 1 of which iss sectional elevation of the weapon and carriage; fig.! is a section of the breech end; fig. 3 is a section of the breech end, with the block or closer drawn down, leaving the barrels free to be loaded; and fig. 4 is u sectional plan, with the cartridges in the barrels and the closer screwed home. This compound gun is com posed of a series of barrels, which are fitted between plates A A, which stretch across from one side to the other so as to firmly unite the two side plates B B, upon which the trunnions are formed for supporting the mitrailleuse upon a carriage, so that it can be moved from place to place and employed in field operations. The rear ends of the side plates B B are of greater thickness than the other portions, and are slotted so that the guide plates of the closer can work therein. These plates are centred upon pins, which are kept in position without working loose by means of tappets acting upon the nuts on their ends. The breech-closer plates G extend a distance beyond the rear end of the barrels, and have near their ends long holes, which serve to hold secure a transverse bar J. The central portion of the transverse bar is of larger diameter, or is thicker than the other parts, so that the threaded rod L, which passes through it, may be turned so as to bring the breech-closer nearer to or further from the rear of the barrels. The front of the threaded rod Lis

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rounded, the rounded portion being fitted between two half plates q 7.

The under side of the closer plate has lugs vv for carrying a pin V, to which the upper end of a link or lever bar U is jointed. The lower end of the link is pinned to a lever Q, so that the closer, when released from the barrels, can be raised and lowered upon their joint pins H H, which are fitted in the side plates B B. The under side of the rear of the side plates has projections for the closer to slide upon as it is being moved, and when it has travelled such a distance as to be tilted, it rests upon a plate h, which forms part of the closer frame G G. The front of the closer or breech block O has a face plate P secured thereto. This plate is provided with a series of holes corresponding to the number of barrels filled in the frames upon the carriage. The holes are threaded for the reception of screw plugs or nipples, through which pins are fitted. The inner ends of these pins rest upon a disc of horn or other yielding material, so that when the explosion takes place the force of the recoil is diminished. The distance the pins may project is regulated by a washer or plug screwed into the back of the plate P. Under the rear of the breech end of the barrels is attached one end of an elevating screw, by which the depression or elevation of the barrels is governed. The lower end of the screw works in a block or socket on the carriage.

The drawing back of the breech-closer is regulated by a hand lever, and it can be retained at the required point by means of a pawl working in the teeth of a ratchet wheel fitted on the side of the frame. When the barrels are filled or loaded with cartridges, and the breech-closer brought in contact with the rear of the barrels by means of the lever handle, the fire can be communicated by means of a percussion cap, or fuze, or quickfire at one side of the barrel framing, which fire is instantly forced through a hole, and impinges against the cartridge case with sufficient impulse to break it and explode the powder therein. The explosion in the barrel causes fire to be driven through another hole, which leads from the first barrel to the second, and this causes the second charge to be fired in the same manner as the first, and from the second to the third barrel in succession until the whole of the barrels on that level have been discharged. The fire then passes up to a second series of barrels, placed above the lower series in succession, and in a similar manner to a third series of barrels. WIL. K. HIBBET.

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THE CHASSEPOT RIFLE. [283] SIR,-The annexed illustration of this celebrated weapon, showing M. Chassepot's latest improvements, will probably interest the readers of our MECHANIC.

In its original form failures occurred in practice with the rifle traceable to the form of cartridge used. It became, therefore, the object of M. Chassepot's later improvements to adapt the gun for the employment of flanged cartridges, and to provide the arm with an automatic arrangement for extracting the cartridge cases. Fig. 1 is a longitudinal section of a fire-arm constructed according to these improvements. Fig. 2 is a section showing the extractor in the act of withdrawing the cartridge case. Fig. 3 is a transverse section through the line 1, 2 of Fig. 2. Figs. 4, 5, and 6 are separate views of the extractor. The movable head shown in the engravings of the first gun is dispensed with, and the caoutchouc obturator is replaced by a metallic piston a. Through the centre of this piston a channel of truncated conical form is formed by the passage of the striker or needle R (which it shortened), when impelled by the spring T. The metallic piston a is lodged in a chamber in the front end of the breech-bolt B, and is held by a screw b passing through the side of the bolt and entering a circular groove c on the outside of the piston. A square tooth or projection d is formed on the periphery of the piston near its head. This tooth serves to operate the extractor. The rear or tail f of the extractor is in the form of a flat ruler terminated at the front by the extractor proper g, which is a curved piece having the form of a portion of the inner circumference of the barrel, and having a recess to receive the flange o of the cartridge. The cartridge is shown in two positions; in Fig. 1 it is seen in the charge chamber, and in Fig. 2 as withdrawn from this chamber. A longitudinal groove or slot i is formed in the rear flat portion of the extractor, into which the tooth d of the piston takes. The extractor slides in a recess h in the bottom of the breech chamber.

The employment of flanged cartridges modifies the form of the charge chamber, and dispenses with the combustion chamber in the old rifle. The rear of the charge chamber, that is, the rear end of the barrel, has a circular groove oll to receive the flange o of the cartridge. A cavity h is formed to receive the ex

tractor proper g, which completes the annular portion at the entrance of the charge chamber. In withdrawing the breech-bolt, the tooth d of the piston a, reaching the end of the groove i of the extractor, draws back the extractor, and with it the cartridge case, which is then thrown out. When a fresh cartridge is inserted its flange enters the recess ol of the extractor, which pushes it into place when the bolt is pushed forward. Thus, the extractor is operated by the bolt both to push the cartridge into place and to extract the case from the barrel.

The screw (which formerly passed through the main or top piece to enter the slotsțin the bolt) is now replaced by a plate p (Figs. 1 and 2), passed through this main piece and hell by a pin r; this piece serves as a tenon to slide in the groove of the bolt B. The tenon on the spring carrying rod 2 is dispensed with, as well as the corresponding mortise in the button at the hind part of the bolt. The whole is replaced by a button or stopper L screwed into the rear end of the bolt. The sight rises on a hinge towards the front of a barrel to facilitate operating it. F. G. R., late H.M.R.A.

THE PHILOSOPHY OF THE ENGLISH
MECHANIC.

[234] SIR,-It seems to me I might speak of the philosophy of subscribing to, and reading carefully such a publication as the ENGLISH MECHANIC. There may be a valuable principle involved: something that reacts on one's own whole temperament. To read and study such a paper will have the same effect on the mind as a good broom in a housemaid's hands upon the cobwebs. The whirr of science clears the crannies and calls thought into action. The perusal of such bustling pages is most suggestive. How can one be idle, lazy, or inactive? One must set to work at something. Just as when I go to church, I fancy I get more good by the trains of my own thoughts aroused than by anything actually said in the sermon (though the trains would not have arisen elsewhere); so also a clever scientific paper sets its readers a-thinking, a-thinking, and not only a-thinking, but also a-doing. Say that I read an

article on astronomy, or perhaps on making one's own telescopes. Very well, then there are those bookshelves. Just so. But what have bookshelves to do with telescopes? Not much, in one way. But think of the philosophy of the thing! The bookshelves ought to have been done "yesterday," and were to have been put off to "to-morrow." But now-Now's the ticket. Thanks to the telescope article, now, however hot it may be, off goes the coat, the shirt-sleeves are tucked up artistically above the elbow, out come saws, planes, hammer, nails, screws, sand-paper, and everything, and the overdue job is done; and it is the telescope artist who has done it, or set it a-going; and who knows but on top of the shelves, when varnished, will be a telescope, as a tripod symbol of success? Thus, in like manner, if you tell a man how to make his own gas, or to construct his own barometer, he may do one or the other, or neither; but in any case you have given him an impulse of energy, a push of progress, quite as accelerating and much more pleasant than a whack over the back with a stick, and a shout of "Go on, stupid!"" The man must address himself to something useful; there is a ring or rattle of machinery in his ears, a gurgle of cogs and drums and bands (of genial industry, not of horrid war). The like is good, whether as work or as play, whether as bearing on livelihood, or as mere hobby and holiday, and every man ought to have his pastime, and be choice about it, because if he has not a good one, he will have a bad one. as amusement, mechanical occupation is beneficial, to body and to mind, to health and to comfort. I even imagine it promotes morality, sobriety, and so forth; at least it ought to do so, and might do so. For example, suppose I have to do with a goodly steamengine. There it is, the Titanic motor, with bones of iron and marrow of steam. I don't neglect it; and why should I neglect myself? Its polished parts are shining, its brass parts are brilliant; there is no rust on it; and why should there be any on me? I can at least be clean. And, mind you, it is not necessary for the hardest-working stoker or poker to be dirty: grease will get off tar; oil will wash off oil or paint; wash your hands in a spoonful of turpentine; a jug of hot water is easily got: get a wife to get it for you: go in for a lump of soap, and a pinch of soda, nailbrush

Even

even, and bath; make the bath yourself, at the worst. At any rate, be clean and tidy, like your steam-engine. Nor do you abuse it or misapply it; it has its oil, its proper amount of drink; and, strange to say, that drink is water. Would water do for me? Suppose I try? I never heard of a steam-engine getting drunk, unless the man in charge of it did, or went mad, like the Yankee regatta of two rival steamers among the suags, where the captain sits on the safety valve, and sings out," Go ahead!" No, my model steam-engine is very sobering; it would get grimy if I let it, but I don't; nor will I treat myself worse. I'll be clean, neat, hard-working, clean again, hard-working again, always sober, never muddled or puddled, always measured, aye, and merry too; as jolly old Juvenal saith, with a sound mind in a sound body. So I beg to enounce that the philosophy of the ENGLISH MECHANIC is the spirit of utility; it sets you on to be serviceable to yourself and to others; not only in great public patents" and improvements, but also in natty tidy home contrivances. And all the while the whole thing in its very essence is a witness for selfrespect, for decency, for personal cleanliness, for sobriety, for home happiness, and all that makes life worth living for. GIMEL.

CURIOUS QUESTION.

[235] SIR,-As a constant reader of the ENGLISH MECHANIC, I have been interested, almost amused, at the amount of disturbance cerebral, literary, and philosophical, which seems to have grown up out of a very simple question, put honestly and singly with a view of attaining information upon a subject of mechanical forces.

That an "F.R.A.S." should have descended into so humble an arena was more than I had presumed to think of. But now whatever may be the tenuity of my own cerevisia, or of Messrs. A, B, or C (a point I am not anxious to settle), the thing I do wish to have understood, and which I probably failed to put with sufficient clearness before, is this:-Suppose a piece of ordnance at any point on the equator, and fired pointblank (or with such elevation as to give the longest range) first to the east, then to the west, in each case with the same charge, will any and what difference be found in the distances to which the shot will have been propelled in this one case or in the other, either the atmospheric resistance arising from the earth's rotation on its axis, or from any other cause. As the earth in its orbital motion carries its own atmosphere with it, it is presumed no difference would R. T. GOULD.

from

arise from that source.

[286] SIR,-In reference to No. 86, p. 378, I would feel grateful to Mr. Proctor if he would favour your readers with his view of this question, taking into account the small quantity DE in his paper on the earth's motien, p. 372, col. 3, of No. 249, 31st Dec., 1869. I observe that when the question is confined to due east and west, as is done by Mr. Gould, and no elevation stated, and if we take the elevation to be = 0, then DE = 0; but the ball must in its easterly motion be retarded by the trade wind, whereas in its westerly motion it must be accelerated by the same cause. I do not suppose, however, that this cause of disturbance is intended by the proposer to be taken into account, and therefore the difference between the east and west motions will = 0, as stated by "F.R.A.S.," p. 395. When the ball is thrown vertically, a condition introduced by Mr. Usborne, No. 143, p. 450, then DE becomes a maximum; and if the height be considerable, say 8,970 miles = earth's radins, the ball would require 2,075 seconds to ascend, and the same time to descend, which would give for D E a very considerable magnitude.

READINGS FROM THE GLOBES.

M. L.

[287] SIR,-Not the least of the numerous and important contrivances made by Providence for the comfort of his creatures is the twilight or crepusculum, by which we are gradually introduced into the rays of the morning'sun, and as gradually transferred from the reign of one mighty potentate to the dominion of his great rival night. Twilight commences with the setting of the sun, and lasts (so astronomers say) until the sun gets 18 below the horizon, when the atmosphere ceases to reflect his rays, and it commences again with the early dawn, when the sun comes again within 18 of his rising point. Since twilight begins at this distance below the horizon, we can from hence calculate at what height the atmosphere has the capability of reflecting the sun's rays. Its actual height we are unable to ascertain, because, being an elastic fluid, it expands with considerable distention the higher it reaches from the earth, and becomes of such rarity that, as far as we know, it exerts no influence upon the appearance of the sun. If it were of the same density throughout, its height could be ascertained with great accuracy from the weight with which it presses upon everything around us; but this is not the case, as every aeronaut has experienced, and as others may learn from their description. The causes of twilight are usually ascribed to the refractive and reflective powers of the atmosphere. By means of refraction we have twilight sooner than we otherwise should; and by reflection it is diffused over all the expanse of the atmosphere. Refraction acts with much greater power in a dense atmosphere than in one of much tennity, and is more considerable near the horizon than at great altitudes, gradually decreasing until the zenith is reached, when 210 refraction takes place. By refraction, a ray of light

July a little above four. There can be no doubt, deteriorated state of our atmosphere has contra mainly to produce this result; and if we take th ber of separate observations as an approximate se sure of this deterioration, the good state is to the af as 3 to 1, nearly. It must, however, be borne in zee that the number of observers in April and M greater than in June and July, and this prope must be modified accordingly. If we enquires spots observed (18) have been affected during unfavourable lunations, the following table, contaur the degrees of visibility for the two sets of two in tions each, with the differences, also the differta ithe two corresponding sets in 1869, may tend to tr date the question:

proceeding from any celestial object is bent, and in consequence, that object appears to our view sooner than it otherwise would. From the same cause, the sun and the stars have a greater altitude apparently than the reality. As a proof of this it is recorded that some Hollanders who wintered in Nova Zembla, some time ago, saw the sun 17 days sooner than they expected, which would not have been the case had not the refractive power of the atmosphere raised that object (particularly as being near the horizon) to a greater altitude than computation made it. It is an admitted fact, then, that refraction makes a celestial object appear higher than it actually is. Thus, in figure let S represent the sun; when, then, the ray S A strikes the atmosphere, it is refracted, and as it is unequally refracted by the atmosphere, the refraction being greater in the lower and denser parts than in the upper, the line A M will assume a curved shape, and become, I suppose, what astronomers call the J & Ju crepuscular curve, and the object S will be seen by a

Obs. Spot

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man at M. If, however, instead of being the ray itself, it were a reflected ray, refraction would of course act upon this ray, too, which would have its share in illuminating the atmosphere. Suppose then an innumerable number of reflectedfrays were in existence; all of them would be affected by refraction, and hence would throw their light, though in a diminished degree, upon the earth; for if refraction takes place upon every celestial object, it must also act upon the rays surrounding that object, and the consequence of this will be that, although we shall not be able to see the sun or heavenly body itself, we shall see the harbinger of that body's appearance in the dawn of the carly morn. Refraction, therefore, has its share in the composition of the twilight, and it co-operates with reflection in gradually intensifying the dawn until it breaks forth into the perfect day. When reflection acts upon the ray S A, it will throw the ray in an exactly opposite direction, and the angie S A°C being the angle of incidence, will be equal to the angle C A M, or the angle of reflection; and hence we shall be able to compute the height of the atmosphere. This, however, will be one ray only; but when millions upon millions of reflected rays pervade the superincumbent atmosphere, light is diffused all around, and animals and men are roused to their occupations, and nature displays her attire to the gaze of all. Suppose, then, that when the sun is 18 below the horizon the twilight begins, then the angle M AS is equal to 162, the supplement of 18; and since the angle of incidence is equal to the angle of reflection, therefore S A C = CA M, or 81°; then having two angles and a side, we can find the hypothenuse A C, which is equal to 4,031 miles, from which subtract C E, the earth's radius, and we have E A the height of the atmosphere, or 49 miles. And we not only can find the height of the atmosphere by knowing that the sun begins to illumine it at 18 below the horizon, but we can ascertain how long the twilight will last at any particular place. If, for the sake of illustration, we take London on June 21, and wish to know the time twilight will continue, we must clevate the globe for the sun's declinationnamely, 234, and having made a mark upon London descend 15 below the horizon, and the consequence is with prepared chalk, we shall find that it will only that there is twilight at that time all night, and the twilight all night will continue until London, in the revolution of the earth round the sun, and in the rotation of the earth upon her axis, reaches 18 below the horizon, or until the declination of the sun is again 20, which will not happen until July 20. We infer, then, that twilight lasts all night from May 23, when the sun's declination is 204, and whilst he is travelling to his greatest declination and back again to 20, which makes 58 days. And if we wish to find the duration of astronomical twilight at any place on the globe, we must elevate for the sun's declination, and notice how long the given place will be before it reaches 18 below

the horizon.

SUMMARY OF OBSERVATIONS.

T. S. H.

SPOTS ON

While

PLATO, JUNE AND JULY, 1870. [238] SIR,-The weather during the lunations of June and July, 1870, has been very unfavourable for prosecuting the interesting series of observations on these objects which were commenced in April, 1869. as many as 242 observations in 37 series were recorded in April and May, 1870, June and July have afforded only 80 in 18 series. The observers in April and May were Messrs. Elger, Prato, Gledhill, Neison, and Whitley; in June and July, Messrs. Gledhill, Elger, Neison, and Ingull. The observations in April and May gave a little under seven as the average number of spots seen on any one evening; those in June and

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1 31 027 *059 +032

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The variations of visibility have been, a ei former occasions, irregular; and this irregular apparent on comparing the differences of 1870 m those of 1869. It is true that in some cases the com of the annual curve is reversed, as shown in No 14, and 16, and this is to be expected with a deten rated atmosphere; still the greater decrease of vis bility of spots Nos. 4 and 14 is irreconcilable upon th view with the increase of visibility of No. 30, Dawes's companion of No. 3, a small eraterlet requiring generally a fine state of our atmosphere to see it. No. 3 has also increased in visibility during the last two lunations. Of the spots which were sufficiently ob served during the first year to afford curves of visibility, the following were not seen during the two lunations of June and July-viz., Nos. 2, 6, 7, 10, 13, 19, and 22; of those which are common to the first year, and the two lunations Jane and July of the second, Nos. 3 and 17 maintain a high degree of visibility, while Nos. 4, 14, 16, and 5 have fallen considerably. Tho only spots which have exhibited a high degree of vesibility under all states of ourjown atmosphere are Nos. 1 and 17, and these, with the increase of such a small spot as No. 30, lead to more than a suspicion that the variations of visibility at all seasons are in a great measure independent of variations of our own atmosphere.

Mr. Elger has pointed out that the markings and spots are so closely connected as to be regarded as cognate phenomena. The greatest number of spes observed on any evening was 8 by Mr. Elger on Jus 10, and by Mr. Ingall on July 14. Nos. 14 and 16 were seen by both observers on both occasions, and the rarely visible spots, Nos. 12 and 31, were seen by Mr. Ingall on July 14. At the same time he noticed the markings, and describes them as appearing with at least ordinary distinctness. He adds, "The whole of the floor at times of fine definition, was covered with spots of light." This is very remarkable, as he appeary to have failed in picking up some of those spots which were frequently visible in 1869, as Nos. 22, 18, and 1, and is strikingly in contrast with those stones of the floor described as "very dark." Can it be that such occasions there is a superficial covering of so kind interfering with the ordinary reflection from th floor? or are the white spots themselves smalle superficial masses reflecting a greater quantity of light! I will forward another extract bearing upon brigh ness and colour in a few days.

W. R. BIRT.

FREE-REED ORGANS v. HARMONIUMS. [239] SIR,-When Debain, of Paris, first invente the harmonium (or, one might more correctly say, tirs brought into the notice of civilized Europe an inventica long previously known to the Chinese under a rudet form), all those of us who happen to be musical as well as mechanical, went into ecstasies about the new instru ment. It had long been a want to provide some keyed instrument for private use, cheaper and less cumbrous than the organ, which would give us sustained tones capable of interpreting organ music. And we thought we had found it. At first the novelty made us blind But gradually (deaf rather) to its important defects. one came to discover that the very best harmoniums have necessarily, from their construction, these very sad defects-1, the tone is of the reed, utterly and irretrievably reedy; 2, the bass overpowers the treble; 3, the intonation is so sluggish that it is only adapted for the slowest of music. And even when Kaufmann, of Dresden, introduced the percussion action to remedy this last defect, although a palliative, it was by no means a cure.

For these reasons I, for my part, and I am sare I may say the same for all my musical friends, had long given over the harmonium as a musical instrument, and relegated it to the country chapel and the schoolroom as an accompaniment for hymn tunes-better, certainly, than the discordant flute, and fiddle, and clarionet, which it very often displaced-but still, very bad, both from the impossibility of distinguishing the air and the impurity of the tone which causes it te cut

through the voices and drown them with its buzz instead of supporting them.

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And in enumerating these defects I do not refer to bad harmoniums, but to the best. The faults are as inherent to a 36 stop Debain, or a 24 stop Alexandre, or e of Schiedmayer's best instruments (and I have tried se) as to a common six-guinea harmonium. entirely given up reeds for musical purposes, d out. Last March I wrote Messrs. Breavington & Son, for a Mason & Hamlin organ No. 46, an 8 stop cabinet withvox humana and two rows of keys. I had grave doubts about it at the time. I confess I read Messrs. Mason & Hamlin's certainly very glowing prospectus of their organs with some suspicion, knowing that folks in New York are not incapable of very tall talk. In due course my organ arrived, and I am not sure I can give much greater praise than by saying that every word of the prospectus I found literally and scrupulously true. It is the ideal of what musicians have longed for in a harmonium. The tone is round and pure, as different to the reediness of the best harmonium as can be. It is resonant, the chords ringing again through the hollow-chambered case after they are struck. The bass does not overpower the treble, but by a particular system of voicing the reeds, every note in the register is of equal power. The intonation is so perfect that the touch is as rapid and delicate as a pianoforte, without any trick of percussion action. It is consequently adapted for any style of music, from the lightest dance Forceaux to the heaviest mass music. Best of all, so pure and true is the tone that even used at full power with four sets of reeds, it will not drown a solo voice.

Now the great difference in principle of construction between the Mason & Hamlin organ and the harmonium is so simple that it is strange it should not have occurred to English builders. Take a violin string and stretch it on a bit of board, and try with a bow to get tone out of it, and we might have come to the conclusion that there was no tone to be got from a string, did we not know that by stretching it over a hollow case instead an Amati violin is made. Messrs. Mason & Hamlin do the same thing with reeds. Each reed is placed in a separate chamber over a delicately resonant sounding box, and the result is perfect organ tone. I would not be misunderstood in using this expression. I employ it in exactly the same way as we say an 8ft. stopped pedal pipe gives a 16ft. tone. The tone is the same though the volume and the depth are wanting. Just so closely does the American free-reed organ approach the pipe organ in tone. As the builders very honestly say, "If you can afford £300 to buy a pipeorgan get one in preference to one of ours, but if you cannot, we can supply you for one-third of the cost an instrument of better tone and capacity than any cheaper pipe-organ." This is undeniably true, as I can bear ready and willing testimony. And as regards even the cheapest American organs with one set of reeds, the tone is as pure, although, of course, the capacity for variety, afforded by a greater number of stops, is wanting. Amongst other differences in construction is the employment of very powerful exhaust bellows, whereby the air is drawn through the reeds instead of being blown into them. Any one who has used a "monthharmonicon" must have observed how much better tone is obtained from it by drawing in the breath than by blowing through it. The reeds are moreover heavier in make, and the tongues of a different pattern to those of the harmonium.

The vox humana is an ingeniously simple piece of mechanism, which produces a delicate effect for solo playing, only comparable to the articulation of the voice, or the vibration of a violin string beneath the bow. So far from being a monotonous and vulgar effect, like the wretched "hubble-bubble" of the old tremolo stop, it is so dainty as only to be noticed when one listens for it. It is contrived simply by a rotating fan at the top of the instrument, which vibrates the air after it has left the reeds, instead of before. The automatic swell is the most perfect I have ever seen, enabling a performer to command the power of the instrument from a whisper, soft and crisp as a musical box, to its full capacity, without any difficulty such as is experienced in keeping the wind in" when playing on a harmonium with the "expression" stop out.

No one who has ever tried an American organ will think of going back to a harmonium-indeed, when one of them is placed side by side with a much more expensive harmonium the difference is so painful to any one with a musical ear, that the buzz and reediness of the harmonium is simply intolerable.

EUSTACE HINTON JONES.

THE CRATER FONTENELLE AND LUNAR
COSMOLOGY.

[240] SIR, The cross westward of Fontenelle, figured by "Foreigner," appears to be nearer to the crater than that mentioned by Beer and Madler, and in the position of their delta. If I interpret the general figure of Foreigner" rightly, the mountain range S.W. of Fontenelle, not shown by B. and M., but very plain on Rutherford's photogram of March 6, 1865, would lie parallel with the S.W. side of B. and M.'s lozenge, which side, according to them, is a broad light streak not shown by Foreigner." It is the N.W. side of the lozenge which contains B. and M.'s cross in the position of their zeta, some distance W. of "Foreigner's" cross. These crosses I have no doubt are formed by intersecting fissures in the mountain ranges. There are two intersecting fissures of the same kind in a depression north of Plato, which may be seen under a suitable illumination, with a comparatively small apertare. It would be well to study these features in connection with surrounding

objects, as they evidently point to seismotic or earthquake action. By the way, this will introduce a few remarks on the letter of "Littus Habet Conchas," who alludes to a continued series of critical observations of the moon's surface as not tending to establish any corresponding physical resemblance between the earth and moon. May I be allowed to ask your correspondent if he will kindly inform me in what work I can meet with such a series of observations? The latest series of seleno-topographical notices that I am acquainted with is by the Rev. T. W. Webb, published in the Intellectual Observer This series includes numerous very valuable observations of his own, but they hardly possess the character of a continued critical series which can be used in finally disposing of the question as to the similarity of the moon and earth, or the opposite, although there are many observations that bear upon it.

For myself, I may say that after eleven years of close observation of the moon, with telescopes varying from 2.75 to 10in. aperture, my own impression is that the moon is more earth-like than it is generally imagined to be. If the reader will kindly turn to page 436 of the ENGLISH MECHANIC, for July 29, he will find mention made of a line of cliffs, part of which form the S.W. border of Hipparchus. These cliffs I have most attentively studied, and I know of none of the features of the moon, and they are numerous, which are more earthlike in appearance. The line of cliffs is exceedingly analogous to a terrestrial coast-line. Whether the "fluid masses," oconpying the interior of the "hollow spheres" of your correspondent, sufficed to produce the appearance of erosion on the faces of the cliffs towards Hipparchus is a question that may or may not be settled by future observations; at all events, all the "hollow spheres" N.E. of the cliffs could hardly have ejected sufficient "fluid material" to have affected them, and it is difficult to understand how the " fluid masses," once occupying the interiors of Halley and Hind, could have eroded the cliffs below them. Let us look at this matter for a few moments in the light that a most careful examination of the whole region will afford. Referring to the article already quoted, south of Halley and Hind will be found a tract of high land, certainly the highest in this part of the moon, and probably the earliest formation hereabout. This high land appears to have been dislocated by a "fault" which is traced to Tycho, on one of the lines of the last distributions and settlements of the typical lava of the burst shells of the spheres. Of the precise nature of the surface at the time when the dislocation took place we are ignorant, especially as to whether the hollow sphere" Hind was then included in the mass of high land, and it is difficult to obtain a true ideal section, but we have good evidence to show that the dislocation took place before the bursting of the "shell," for in its neighbourhood the "fault" is certainly interfered with by the grooves, which are apparent on the sides of the "crater" Hind. After this the evidence is strongly conclusive, either that the cliffs before referred to were raised, or that the surface N.E. of them subsided, for they cut off abruptly the slopes from the "crater" Hind. And here we may institute a comparison between the apparently more ancient craters Hind and Halley (premising that the "hollow sphere" Halley burst after the cliffs were formed), and the more recent one Aristillus on the Palus Putredinis. The result of such a comparison I leave with the intelligent observer, who is acquainted with the agencies producing and affecting our geological phenomena. Do not these successions point to such slowly operating agencies as we are familiar with in the earth's crust, and cannot we find terrestrial analogues to lunar craters, such as Hind and Halley, on the earth's surface? for example, Santorin, and such as those partly filled and broken craters on the borders of the Maria, on our sea coast-Torbay, for instance. May not so close a scrutiny as the lunar Hipparchus has undergone, when extended to the whole moon, contribute to the detection of an increasing number of terrestrial analogues?

In conclusion, I would just remind the reader that the article "Telescopic Work, &c.," on page 418, contains a description of the formation adjoining that sketched by Foreigner." W. R. BIRT.

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ON THE LINK MOTION.-LETTER I. [241] SIR, Mr. James Harrison has written a letter on the subject of the "Link Motion" in No. 275 (July 1st), in which he reiterates with amusing earnestness his erroneous opinions concerning it.

He says, if I (J. B.) "was well versed in link motion, I never would have said that the whole amount of vibration must be communicated to the centre of the link." I did not say anything of the sort, as any person can see by reading over my letter in No. 273, June 17th. What I did say is this:-"That the amount of vibration that the middle of the link should have is found by adding the lap and lead of the valve together, and multiplying the sum by two, and it must have that amount, and impart it to the valve-spindle too, or it is all wrong;" and I hope to be able to make Mr. Harrison understand the truth of that proposition, and the practical necessity of carrying it out in the steam engine, before I have done with him.

In the letter alluded to, I gave an instance to illustrate this rule, in which the valve has 14in. of lap, and fin. of lead, which together make 13in., and multiplied by 2 give 34in. as the proper amount of vibration for the middle part of the link; but in that instance I said nothing at all about the throw of the excentrics or the full motion of the end of the link, because I was then merely proving, in a rough way, the necessity for

motion at the centre, and giving the rule for finding its amount. The motion at the end of the link, or the full amount of vibration," is another thing altogether, and is of course always much greater than the centre motion, but is never any particular measure of it, as the amount of end motion depends upon the greatest length of stroke the designer wishes to give the valve; and the centre motion is fixed, as I have just said, by being made equal to twice the sum of the lap and lead, or twice the "lineal advance" of the excentrics, and this is what we might call the normal vibration of the link centre, which is increased by the crossing of the rods in one arrangement of the gearing, is decreased by the same cause in another arrangement, and is neither increased nor decreased by a third arrangement; but all this will be explained further on.

Mr. Harrison still " emphatically denies" the existence of any motion at the centre of the link "when that centre is in a line with the valve spindle and crank shaft, and the diametrical centres are in opposition to each other." He also says that, "both excentrics have the one throw" (right), "and travel one distance" (right), "and at the same speed (wrong), "but in opposite directions (wrong). The excentrics, and of course the ends of the link, move for a considerable portion of each revolution in the same direction, and the reason of that is, the centres of the excentrics are never set in diametrical opposition to each other, as Mr. Harrison supposes, but in practice are always placed more or less on one side of the diameter line.

A line connecting the centres of the two excentrics will not pass through the centre of the shaft, but is always some distance from it, and that distance is known amongst engineers as the "lineal advance" of the excentrics, and its amount is determined by the amount of the lap and lead of the valve. I have no doubt, from Mr. Harrison's writing, that this is the first time he has heard of the "lineal advance," for if he knew anything about it, or its objects or effects, he could not have perpetrated so many blunders in so small a space as he has done; but if he has patience and humility, and aptitude to learn, he may acquire some knowledge of the subject before I have done with it.

But even if the excentrics were set without any "lineal advance," and with their centres in "diametrical opposition," Mr. Harrison would be no nearer right than ever, for the centre of the link would still have some vibration due to the crossing of the excentric rods, as I explained and illustrated in my last letter; and the exact amount of this vibration would depend upon the length of those rods, the length of the link itself, and the throw of the excentrics; and this centre vibration can never entirely disappear till Mr. Harrison, or some other person, makes a link motion in which. the excentric rods will have infinite length, the link itself no length at all, and in which the circle described by the centres of the excentrics shall be no larger in diameter than a mathematical point; or till he produces a link motion in which there shall be no crossing of the rods; and that, I may as well tell him, is quite practicable, and at the same time quite useless, for a motionless centred link would not do for working a slide

valve at all.

I will now proceed to place before Mr. Harrison and "our readers" the link motion as it really is in practice, and I will explain and illustrate the principles of that very simple, beautiful, and imperfect contrivance in the plainest language I can command, so that even Mr. Harrison, and other gentlemen like him, who have yet to learn the very ABC of the business, may be enabled to understand it.

Fig. 1 is intended to show the mechanical impossibility of constructing the ordinary link motion so that the centre of the link shall have no vibration. The centres of the excentrics are set in diametrical opposition or without lineal advance-that being the position in which they impart the least motion possible to the centre of the link; and whatever the amount of centre motion in this case may be, it is caused entirely by the crossing of the excentric rods, which crossing is an unavoidable necessity of the case, therefore, motion-more or less-at the centre of the link is unavoidable; but we always want a great deal more motion at the centre than is imposed upon it by the crossing of the rods, and this additional motion is got by placing the excentrics so that a line connecting their centres shall be at the required distance from the centre of the shaft-and this is the lineal advance as explained above. In all these figures the excentrics themselves are omitted, the centres only being retained as all that is necessary to the explanation.

In Fig. 1 there are eight different positions of the gearing shown for one revolution. This figure is drawn from an actual half-size model which I have had constructed especially for the purpose, and the amount of vibration at the ends and centre of the link is faithfully shown; the excentric rods are 3ft. long, the link is 16in. from centre to centre of excentric rod ends, and the circle described by the centres of the excentrics is 8in. diameter, consequently the ends of the link have Sin. of vibration in all positions of the motion; the link is suspended by the centre, and the length of the suspending bar is 21in. The amount of motion at the centre of the link is 13in. In my former letter I said it was 2in. for a similar valve-motion. I took that from an inch scale drawing, hence the slight error; but 1in. is the exact thing, and is what the model shows. C V is the main centre line of the crank shaft and valvespindle. The link is shown in "middle-gear"-as it is called-with its centre opposite the valve-spindle, or in the position in which Mr. Harrison "emphatically denies that the centre of the link vibrates," as if its position with regard to the valve-spindle could in any way affect its motion. How could it? The motion of

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