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what would now be termed, in music-hall phraseology, "a lady vocalist," i.e. Miss Brinkloy, as early as 1767. Ho might as well also have stated that the elder Dibdin was the accompanist in this first recorded public use of the pianoforte. The instrument he used might have been а pianoforte proper—which, it having been announced by that name, it probably was—or it may havo been a hammer harpsichord of English or German manufacture. There is no impossibility in its being English, for wo have home-made pianos a year older, not to mention that the "apostles" might then have been hard at work converting the musically-bar barons natives of England from the idolatry of harpeichordism to orthodox "pianoforte ism," with a success rivalling that of the South African bishop, whose missionary labours among that little known native tribe of African idolators, who rejoice, or ought to rejoice, in the euphonious name of Kauoodoodoodooldums, were, in both .senses of the word; so very "graphically illustrated" by the clever author of the celebrated Bab Ballads.— N.B.—He wrote this veracious (for as the noble author of "Zanoni" would hare put it, he presents to us the real, if not the actual) hietory of that bishop's Christiimlike doings, in the way of reconciling religious differences, in a most earnest and truly Christian spirit, although truth compels me to confess he only did it in "l*'un."
I feel tempted (onjy just for once) to digress, and say л few words about Dibdin. This musical genius, who built the Circus, now the Surrey Theatre, another theatre in Beaufort-buildings, which ho named the Sans Soucy, and yet another which he colled by the same title—now, I believe, the auction rooms of Messrs. Bonhams, in Leicester-place, from whence I have abstracted (after paving for it) many a pleasing picture, not to mention " certeyuge and snudrie" pianofortes and other musical instruments. Dibdin, was, I believe, the first Englishman who gave musical entertainments unassisted. For some of these he composed his cele-, bmtcd nautical songs, one of which asserts that a sweet—(well, he might be sweet, all things considered) —little cherub sits up aloft, for the humane purpose of *' looking out" for the life of poor Jack. How he, with his peculiar conformation (which however much it might conduce to sweetnets, and if not light itself, certainly lightness, as every Christian is so posteriorily constituted as to require the assistance of Baxter'.: celebrated back "shove" can testify) could sit, is just one of the many things no fellar can understand. Dibdin's sea songs were extreemly popular in their day, and had the credit of greatly assisting to man the navy. I should be inclined to suspect that with all our Jock Tars' patriotism (often accompanied by a strong desire for prize-money), that constitutional safeguard—yclept the pressgang—now, I am very sorry to say, a thing of the past, for Conservatives to regret—had just u leeue to do with this matter. But then John Bull has long worshipped shams; why should he not worship musical shams as well as others?
Dibdin was accustomed to accompany his songs by & very complex musical instrument of his own design— a sort of organized piano—which I believe had pipes, drums, bells, triangles, and other sources of harmony (query of noise and dissonance), which my own father —who knew him personally, and often "sat under him," I mean attended his performances—told me was very effective indeed. Now I have heard several similar instruments of English and foreign make, and, in а certain sense, I have no donbt whatever it was like them, very effective. The poet says or sings, 'Tis distance lends euchautment,—certainly quite as true of tho wholo generation of such "stunners," as it is of any view, earthly or celestial, within tho power of our telescopes. Nevertheless, I should be very glad to know what has become of it, and see it added to that collection of queer old odd fiddles and other things in the Museum, which Punch's polite juvenile miss very improperly termed /чипу, to the horror of her governess, who very properly told her never again to use so shocking a word in public, most especially not in the sacred precincts of South Kensington Museum; for said she, "Government objects to such a term being used to describe works of art. My dear, you oug i. о say * curious' or 'very remarkable,' and nev>e ^o use so vulgar a word as funny," I .trust, if Dibdin's instrument is yet in existence, its present owner will either present it to the nation or sell it for a valuable c-o-n-s-i-d-e-r-a-t-i-o-n.
That the pianoforte superseded the harpsichord in the theatrical orchestra at a very early period is an obvious mistake. I must doubt — although often employed to accompany the voice, when it wa3 wheeled on to tho stage when needed—that it did so generally until about seventy years ago, perhaps not so soon; for until about 1810 it was so weak in tone that the harpsichord continued to surpass it in power. One of the most powerful harpsichords ever constructed was burned in the fire which destroyed old Covent Garden Theatre; but whether another succeeded it in the new structure, or it was replaced by a pianoforte, I have been unable to ascertain; but I rather think it was so superseded; for I do not remember that the old harpsichord maker I knew, who was about seventy years of ago in 1833, and who was very enthusiastic about the burnt harpsichord, ever told me that it had a successor of the same species as itself. As he was very familiar with the lost one, and, until I showed him mino, would not believe it was possible to make one which could exceed it in power, and felt great interest in this and other harpsichords generally, often lamenting our degenerate modern taste for tho piano, I think he would have told me if it had not been the last of its race in the Theatre Royal Covent Garden. I have since feared showing him my instrument was an act of cruelty to the animal, for it dethroned his favourite idol; he was compelled to admit the greater
power of mine, which is the only instrument deserving the title of "consort" harpsichord I have had the pleasure to hear; butas a description of it is published in No. 276 of the English Mechanic, I, as usual, eschew vain repetitious.
It is quite certain the piano did not come into general use as a solo instrument in the concert-room until the masterly playing of Musio dementi was heard, and "took tho town by storm." Not only was Clementi a very " stronghand " on the harpsichord, but, for his time, a very great pianist. Some of his compositions are far from easy. The great Thalberg, at the Exhibition of 1851, told your very practical correspondent "W. T." that, excepting his own compositions, he seldom or ever practised anything but "dementi's Gradus ad Parnassuin," a work! strongly recommend to the whole generation of young lady players, it being a collection of remarkably "ea»y" exercises. When they have mastered them, they uee«V little feax anything else within the reach of their fingers. Indeed, if young ladies* hands could command twelfths, I ¿bar we should not greatly admire them— I mean the hands, not the twelfths—any more than we admire big female feet; for, be it known to all men and women, that the female foot should not quite equal the Queen's foot—I înr.an the third part of her standard yard—or twelve inches imperial measure.
Our pianoforte historian seems strangely misled by hie reading. "How readeet thou," is a question I think it would sometimes puzzle him to answer. He says that very ingenious mechanician, Merlin, tried in 1774 to effect a compromise between tho harpsichord and piano (by combining both), which had theu nearly superseded the former. The patent of Merlin lies before me, and I can find no trace of any attempt at compromise in it. Merlin simply proposes to do, by better means, what had been done on the Continent, and probably in England also, at least half a century before his time—viz., to put hammers to harpsichords in addition to its jacks. That he afterwards constructed three unison grand pianos, with jacks added, is nothing to the purpose. Robert Stodart did it soon after; and so far from this indicating that the piano had superseded the harpsichord, it rather indicates that the harpsichord yet maintained tho lead, or at least, yet had so much influence that the pianoforte-makers thought their instruments could not stand alone. So far (from tho piano having generally superseded the harpsichord at this time, it is likely that if the books of Tschudi, Broadwood, Л Co., and Kirkmani Co., were obtainable, they would show more than а score of harpsichords made for one grand piano; and probably if we had similar returns of all the small pianofortes and spinets, the latter would show a very large majority, although perhaps not so large as the preponderance of the number of harpsichords over grands.
Probably Robert Stodart never made a harpsichord proper in his life; but eren he, by the invention of л check inserted into the key, remedied the chief defect of Christofali's action—viz., the long drop of tho hammer into its cuneiform rest after the hopper had been " set-off," by means of this check, probably gave the grand pianoforte tho greatest impetus towards its adoption for use in the concert-room it ever received; for from Stodart's time until the so-called double action of Sebastian Erard was invented but little further improvement was made in the mechanism of this instrument. Indeed, but little more was required to make it as perfect as any mechanism could be, in which the hopper is made to escape from beneath the shoulder of the hammer butt. Erard first showed us how to do this, and yet to retain the capability of repetition, formerly confined to single actions without checks; but like most inventors—I plead quite as guilty myself of committing this fault as any one who has at tempted to improve pianoforc actions can do—he first did it in a very complex, however efficient manner. From the sin of complexity, that firm are yet far from free. ЛУНЬ all tho consideration due to commercial requirements, and making every allowance for tho very natural independent feeling which renders first-class firms unwilling to adopt the improvements of small makers, however excellent their designs may be, I have often wondered that Messrs. Erard have not adopted Stumpfs modification of the principle of their own action, which I find does its work in my experimental grand piano equally well, if not better; i.e. it enables the player to repeat the blow with the key equally low, or even lower than can bo done with the mechanism used by Messrs. Erard—for I can do it with certainty, by allowing the key to rise rather less than tho sixteenth part of an inch, the hammer being effectually checked between each blow, however rapid the repetition. Surely it would be no dishonour to Messrs. Erard to adopt what is only a simpler and improved method of carrying out tho principle of the invention of the talented "founder of the firm, especially when it is considered, that by doing it, the action is so greatly simplified that the number of centres of motion is reduced from six to two, irrespective of that of the damper. Through error we arrive at truth, and through complexity we—in mechanical designs and constructions—arrive at simplicity.
Merlin's, and his predeoessors', combination of jacks with hammers, afterwards carried out by R. Stodart and others, is very effective when properly done. I knew an instrument of this kind, with two ranks of keys, in a satin-wood case, compass five octaves complete, i.e., 61 semitones, which bore the uamo of Longman and Broadrip, A.d., 1790, the samo date as my harpsichord. It was a vile piano, restrung with three about No. 8 wires to each note, but tho harpsichord action brought out very fair tone, excepting the bass, which being strung much too light was weak. I think so well of this combination that it is quite possible I
may carry it out in a bichord grand ¡ it affords a very pleasing variety.
In page 52, Mr. Brinsmead describen what is termed the old man's head actioji, i.e., the hammer lifter, which does not еясаре or hop off like the hammer lifter of a modern piano, whence its not very appropriate name of grasshopper. N.B.—The inventor «>f this was not John Gieb, as Mr. Brinsnieadi who copies tho mistakes of others, states, but Cbñstofali, whose action has a trae escapement.
It is by no means " sartohi sure" that the old man's head is the very oldest of pianoforte actions. I have gone into this subject in another paper, but will just say thai the first record of its alleged invention by Schroeter, A.D. 1710, is subséquent to Christofah's escapement action. Maybe the tangent of the clavichord, with clothing on iU top, had been used to strike strings [a la dulcimer) before any old man's head (in»4* a musical instrument) was treated—as it was the onetom to treat a traitor's, i.e., stack upon a stake or pole—for the tangent wire fulfilled this duty to the head of "ye aucyontc man" inside the, perhaps, reversed dulcimer or clavichord with open strings tuned to the chromatic scale. This kind of old man's head, however "soft "(young men's head» never are soft of course), would not " damp," i.e.. stop the vibrations of a string, unless held against it, any more than a modern pianoforte hammer does. Unless the player lifted his finger instantly it would indeed block most "consumediy ;" but it is astonishing what you con do when you are used to it—like the lucky eels who were benevolently supplied with many skins, and had to endure their being successively taken off. We have Sterne's authority that it was nothing (query, to than or the fishwife ?) when they were used to it, which they could not well have been if they had not been mercifully provided with many cuticles. I have seen a pianoforte maker's shopman—I sincerely beg his serene highness's pardon for giving him a designation so infra dig., I should have written gentleman ; of course they are all gentlemen in so refined a vocation as pianoforte making—the gentleman, I was saying, who condescended (for a consideration) to play very pleasingly on the instruments in his employer's shop, and to exhibit their excellences (and hide their defects also) from the would-be purchaser, who, probably from his" touch'' not having been sufficiently " cultivated," could not play on any of them at all. I say I have seen him ran his fingers over the keys of an instrument (every hammer of which blocked dead against its strings), and lift up each finger from the key just as if the latter had been a " hot potato," supposing so refined a person could have conceived the existence of so vulgar a comestible aa a hot murphy necessarily must be, for " are they not sold in the streets," certainly not so cheap as sparrows during the first century, for we don't buy that poor man's luxury, the "hot potato "—by the way, it is considered rich man's luxury at Evans's—quite so cheaply as the market price of sparrows—i.e., two for a farthing—onery some other fraction of a denarius. Can it be possible that Queen Anne's, or any other farthings, were then current in Judea? But not being a numismática! any more than I am a mathematical person, of course I cannot possibly know that Cresar's image and superscription were not impressed on farthing*. But to come back to our subject, after this slight digression, or compound of digressions, I remark that Mr. Brinsmead states that with the old man's head action the blow was very feeble, but I may also remark this is not an essential character of that action; indeed, there can be no difficult v whatever in perceiving that it might be made to impel the hammer with as great velocity, and consequently cause it to strike as forcibly as the common grand or any other action can do. Nay, if the old man's head be wide and 1hin—I forget tho ethnological word for this conformation—and it be stuck up rather high (d la traitor's) it is obvious that it will approach nearer to the hammer's centre the further the keys be depressed in front. Now, this condition of things, so far from causing the hammer to strike a feeble blow, conduces to the very reverse ; for it is obvious that the nearer to the hammer centre the old man's head, or lifter, acts, the faster C.P. it must impel it, and the merest tyro in mechanics knows that the faster a hammer of given weight be impelled tho harder it strikes. But, as many persons resemble the writer in desiring the expérimentai* erucií, they can—if so minded and desirous—give the policeman on the "beat" half a crown to try the effect of striking their own whole one with his truncheon when moved at greatly varying velocities. After they have had sufficient experience I can assure them, supposing their previously whole crowns be not "crackit," as the Scotch say—i.e., made into half-crowns, or yet smaller fraction» (I hope not vulgar fractions)—in other words, if their thick skulls be not fractured, and their memory totally destroyed by the experiment, that their doubts will be completely solved, and they, being saved by suffering, will become true believers ever after. I fear I shall get but the *malt thanks for this benevolent good advice (gratis), which, the poet says, is yet its market price.
I have been induced to favour the gentle reader with this analysis of tins perhaps oldest and most primitive of pianoforte actious, because in comparatively recent times the old man's head—like that of an irrepressible nigger—has popped or cropped up again. The grand pianoforte mechanism of Messrs. Hopkinson is an arrangement for making the old man's head—in this case literally a wooden head, as usual, but with his hat off— do modern work, and I must say they have made him do his modern work extremely well. Instead of putting his head on an indexible pole (like that of an ancient wrong-doer, treated secundum artem, according to the humane practice of our ancestors, who put tho dangerous class speedily out of pain, and thereby saved no end of money in county rates and model prisons), Mfssi-.-í. Hopkinson put it on a U-j, with a knee joint, но that hie old bead (modernized to nuit the requiiemente oí a pianist of this period) might be madu to bow to the requirement»* of modem society. In their action the old man's head, although tí be but a wooden block, cannot block the hammer against the string, bocauRO,aa in our Schroeter'a and Mason's actions, it cannot lift it quite up to the string—in a word, he is a short-legged onipede. N.B.—This action, although but a onelegged affair, cannot possibly be made to resemble "our Mary Anne's letter," for it don't come (or go) hopping. Unipedü as it is, it cannot hop—ergo, it is not properly what is termed a hopper, or, somewhat absurdly, the grasshopper action. To prevent the hammer from rebounding from the old man's head, a habit it had, which was —however soft that head might naturally be, or however soft artificially it might be made—the torment of the player, Mesara. Hopkinson apply Ilobert Stodart's common grand chuck to it; and it is in making provision to allow the further descent of the key, which would otherwise block the hammer against the string, that the ingenuity of its designer, (whose name is Mata, if I don't forget), is displayed. This is effected in manner following :—that is to say, when the lifter has raised the hammer as nearly to the string as it can safely be adjusted to do, a lever comes into action which compels the old man to bend his knee-joint. This not only prevents his head from rising any higher, but actually compels him to do the polite by lowering it. Under these circumstances it is obvious that not only does the further depression of the key bring the check witliin thu radius of the hammer's circular path, but it also, by shortening the hammer lifter, affords ample room between its top and the shoulder or surface of thu hammer butt (against which the said lifter acts to raise the hammer) for the hammer to fall against the check. Thus it will be perceived that there is no escapement or hopping off, proEerly so called, no danger of blocking, but also comined with absolute certainty of the checks acting properly. I need hardly add that the hammer strikes the strings with just the same force in this as it does in every other action which impels the hammer at the same rate. It cannot be greater or less so long as its weight and velocity are unaltered. It is, in my opiniou, one of the very best grand actions in use. It feels extremely nice under the finger, enables the performer to play with great expression, and repeats the blow by a very small rise of the key in front, which is a combination of very good qualities.
The remainder of this more or less veracious history I have already characterized. It consists chiefly of matter wuich Rimbault thought good enough to print, A.d. 14Ö2, from whose work it is copied almost verbatim, even down to the list of patents for so-called improvements in harpsichords, spinets, pianofortes, &c., but in this matter ho has indeed gone beyond his predecessor, who terminated the list he published in löÖ"2, with Hopkinson A.d. 1Й51 ; following so worthy an example Brinsmead terminates his list, published in 1&70, in the year of grace 1862, with the illustrious name of John Broadwood—I beg pardon, I ought to have written, my only excuse is that old associations have euch power over us—the illustrious name of John Briii s mead, the alleged father both of Edgar and of cheap pianofortesrEureka, Млдпш, e*t peritas et prev€tlebit (query, will, in time, pre wail a bit). It is, of course, quite indisputable that among the many patents which have been taken out for improvements in pianofortes eince Brinsmead's crowning mercy, A.d. 1НЙ2, there could be not even one worthy record, no doubt filial veneration—not to hint at commercial interests—compelled our " Sweet Edgar"—by thowayl fear the name of the "sweet " individual recorded by the poet was uot Edgar bnt Edwin, but n*i mporte, both at least are genuine Saxon, and, as the very practical Yankee philosopher put it '* it's all the same and it don't matter." After such a " crowning of the edifice " with the name of the author's respected progenitor, it would ill become a mere outsider, like an ignorant blacksmith, to comment on the refined tasto (combined with a somewhat acute perception of probable material advantage), which is exhibited by the exclusion of so many more recently patented inventions. So having, perhaps you will think, said quite enough already (I fear too much) anent this matter, I to the great relief of yourself and your readers, only say one word more, which word is, Finie. Тик Harmonious Blacksmith.
just been finished) with the same weight as before. Now there were parties there, like somo of your correspondents, who thought the valves were spoiled, and that if the regulator leuked the engine would not stand still ; but, to disabuse these parties of their prejudicial disposition, I brought it to the level, placed the lever in the centre notch and turned the steam on, but could not get a puff out of her, but by shifting the lever a notch or two she answered to it immediately, but by bringing the lever into centro notch again she came to a stand-still, with the steam on all the time. This, I think, will be proof sufficient for Mr. Wheatley that the centre of link has no motion, provided the excéntrica are in their proper places.
I will now say a word or two to my friend James F. Ryan. Whenever he makes a drawing of excentric never let the excentric rod point to the diameter ; that is not its proper place. The place for it to point is the common centre of excentric, and its vibration is something less than the throw of the excentric vertically each sido of the horizontal line. I am very thankful for the diagram for my instruction (or rather destruction provided I swallow it), but beg to say that it is a waste of space, as the same diagram is the production of Mr. Baskerville, of the 17th of June. It is the taking of the diametrical centres that is leading them astray.
I now ask Mr. Wheatley and Mr. Ryan of what use are so many notches in quadrant if we have so much motion in centre of link? I always thought the first notch from centre was the minimum, and the end notch the maximum; in fact, common sense must tell them that a link 1ft. 4in. long travelling 5Jiu. each end, but in opposite directions, and each end making the return stroke at the same instant, must make some part of that link motionless as it were. If we put the lever in centre notch we have no motion in valve, but if we place it in next notch we have the amount of motion, and, as I said before, the maximum is when in end notch. Now how can this be unless the centre of link is, as it were, the centre of motion to two distinct levers? If we saywe have l2\in. of motion in centre of link then we might say that we have three motions in that link— one to run the engine the right hand, the other to run it the left hand, and the third one (which is the 2$т. Mr. Ryan speaks about, and the 3$in. Mr. Baskerville says the middle of the link should have), or that supposed to bo in centre of link, is to run the engine any or no way, but which is the very tiling J. W. Bedford wants to'get without—viz., " steaming and exhausting when the lover is in centre notch."
Iu conclnsion, let these gontleinon draw out a link lft. 4in. in length, and take njin. as vibration for valve; divide one-half the link in four (treating that half as a lever whose centro of whole is as centre of motion), and we shall have for the end notch 5Jiu. of vibration, and for the next 4in., the next 2fin., and the one next to centre notch l^iu. of vibration respectively; and thus we require nine notches in quadrant—viz., four each sido of centre notch corresponding to the four divisions of one-half the link, consequently giving ns complete control over the amount of opening required for that valve, to suit the difference of loads the engine has to lift or draw. James Harrison.
 Bra,—I am sorry I replied to Mr. Wheatley во rashly on p. 352. I ouçht to have taken more time to think it over; but as I am not at home until tho week's end, nor do I see my Mechanic until then, I could not possibly reply as I should have done; this, and the way Mr. Wheatley commences his attack, led me on rather too rashly, but I will endeavour to do better in fntore.
I am very thankful to Mr. Wheatley for reminding me of my want of know ledgo of the link motion. He яауа he is afraid "I know very little of the link motu»." I may inform Mr. W. at once that I do not know very much about it, not one quarter of what I ahonld like to know, but what I do know I have proved by experience, having applied tho link motion to Cornier* valves as well as slide valves. I have aleo seen the link worked with one excentric and rod. Now if he will make a model of tho former (Cornish valve), and one to the latter, I think ho will know a little more about this motion by the time he has done во. I may state for the last five years I have liad a locomotive to keep in repair, and about two years ago I had to tabe all the lap off to enable it to go up au incline (that had
[10.1] Sir,—I have read with much interest the discussion on " Link Motion " carried on in the columns of our Mechanic, and think that it will go a great wav in clearing up tho very hazy notions entertained by the great majority of working engineers on this beautiful motion. Will you kindly give me space to correct an error into which Mr. Ryan has fallen in the diagram sent for the instruction of Mr. Harrison?
In the diagram in question, with the excentrics in the position shown, the rods ought to be created. This, it will be evident, very much reduces the amount of vibration. It is quite possible so to proportion the length of the rods that there shall be no vibration.
R. H. M.
HARMONIUM REEDS—THEIR CHANGES IN PITCH.
 Sin,—We ought all to bo ready to obey the new "order," which, in right of your premiership, you have issued, calling upon us to see that no question goes unanswered. Every one must acknowledge it to be a good stroke of practical wisdom to exhibit weekly the "unnoticed queries," and it should be a pride amongst the subscribers, each in liis own speciality of acquirement, to keep the list within the least possible limits. Mindful of the duty, I reply to thoso questions which have personal reference to my own studios.
"Amateur Tuner" (4295, p. 407), enquires concerning the tuning of harmoniums; tho remarks I mako will abo answer the question of "J. H. F.," some numbers back, on the subjoct of tuning. The observation of an amateur tuner is quite correct as to facts: harmonium reeds do fluctuate in pitch under variable pressure of wind, and necessarily во. It is tho nature of tho free reod. "Freedom" presupposes tho tendency to go astray. Stronger wind sets a greater portion of tho reed in motion than an average pressure does; lighter wind throws loss length into vibration, therefore virtually tho reed itself varios in length. In fact, the reeds never vibrato entirely up to their roots, but only more or less in extent according to the degreo of force exerted by the wind upon them. Within average forco the differences of pitch arising are scarcely observable, although wo know they must exist; but when the flexion becomes a strain on the fibre of the metal then the variability reaches extremes, producing dissonance.
The predominance of such fluctuations will very greatly depend on the character of the sound-board.
Improperly scaled channels favour discrepancies of pitch, whilst truly sympathetic channels have a compensating influence, restraining the wildness of the variations.
The defect is not peculiar to harmoniums only, it pertains to all wind instruments, and is but partially overcome or modified by art. The student would do well to remember that every art is a compromise, whether in governing man or materials. After all the skill of the maker has been exercised every instrument betrays imperfections. The soloist on a wind instrument finds that an art of intonation is required, he needs to tone each note as hu wants it, and excellence in this gives him supremacy amongst his fellow artists. Tho questioner will immediately respond—" I would know this art,"—we can only reply that he must acquire it in patient work ; it cannot be told. When we are engaged in finishing and perfecting an instrument we are rehearsing the part of thu artist who is to play upon it, reducing the imperfections of intonation, and, as far as possible in us lies, are smoothing the difficulties ho would have to conquer himself before his music could give the satisfaction to tho ear which both artist and audience desire; hence the anxiety of the artist to obtain a fine instrument—henc\j the ambition of the maker to produce one. Yet tho finest possible instrument leaves full scope for the artist, only that it permits him to devote his, skill to tho finer grades of excellence, the rougher work has been done for him in patient rehearsals and repeated trials of effect.
Amateur musicians, like amateur politicians, are too much bent on demanding a system ol perfection—too much inclined to rely on formal methods, and to think that everything may be done by rules and regulations. In respect of musical instruments they will soon find it is not so ; experience will show how much they must of necessity yield to tho peculiarities they meet with in order to attain real utility. It is best to recognize defects as inherent in the nature of the harmonium, and we are then better able to judge how far they are to be influenced by skilful treatment, or veiled by art, and perhaps mado subsevient to agreeable results. Tho practice of tuning, although so important a matter for music, is but distantly related to musical feeling; it is an arithmetical operation, a calculation by the ear. Many of the best tuners have been шеи without musical knowledge, and devoid of musical feeling; the talent is special, like tho talent for figures, even as a man may bo a good accountant yet possess no aptitude for the conduct of trade, or may be a good architectural draughtsman, yet have but little sensibility to the) painter's effects of colour. Suppobing a man has a talent for tuning, it will require from two to five years practice to render him competent. I cannot, therefore, advise the amateur harmonium builder to undertake tuning his own instrument; his desire of assuring his friends that he did everything himself ho had hotter sacrifice to the more humanising regard for his friendo' ears. It is hardly probable, under the most favourable suppositions, that he would be successful in his early efforts in tuning—his time would be wasted aud the practical usefulness of his instrument be lost; for I take it to be that it has somo musical service in its design, and has not been got up as a child's puppet-show for friends to be condescendingly interested in. An harmonium intended for use should, if possible, be tuned by a practised tuner, who, if only of moderate skill, will have an advantage over an inexperienced hand. It is then open to tho possessor to make whatever incidental changes his own taste may suggest ; indeed, it is likely that minor changée and shadings may be desirable, for it is not every tuner has an ear for quality, and the amateur who possesses the higher susceptibility to musical feeling may thus find ample range for exercising his skill; and should his temerity lead him to any extravagant temporary derangement the tuner will be able to bring it back again into a sane condition.
The amateur bent on experiment and content to spoil a set of reeds would do well to get up an extra specimen and test it by side of the professional work ; he will learn more by this than by his own unaided efforts. Instruction in the arithmetics of tuning should be Bought in one of tho manuals on the subject; unless entered into with thoroughness of detail an exposition in these pages would be useless, and therefore I prefer to advise the study from its rudiments. A little book, at a shilling, called "D'Almaine's Art of Tuning," may be obtained through any bookseller.
In the process of tuning tho bellows should always bo kept as nearly as may be at one even power, about half tho strength of springs, remembering that single notes tuned wül show more variation under changing pressure than will be exhibited in actual u*e when chords and running passages distribute the strain of the wind. A discreet tuner strikes the mean in the general display of the instrument, humours each reed according to its strength or weakness, and endeavours to leave it in that condition which, on the whole, will be most generally serviceable in combinations of chords and most agreeable in the average effect; for the tuner should also be able to associate the voicing and regulating the reeds with tho more mechanical operation of tuning. The ability to do so is rarely found, but when it is, that tuner is highly prized. No two tunera tune exactly alike, and there are different systems of tuning adopted from personal preference. It is an accepted doctrino that all octaves should bo tuned perfect. As regards the harmonium this doctrine I do not hold to, believing it can be shown as theoretically reasonable, and practically more agreeable that they should be something less thon perfect; but this and many other matters in tuning form too complex a study" to be understood by a merely curvory explanation. Hermann Smitii.
 6ib,—In accordance with "C. G.'s" request (p. 480) I give him a method by which he may find the proper diameter of a plan for any sized Newtonian reflector.
The aperture of the speculum being given, its solar focal length is next found, anda diagram (similar to that given above) is to be correctly drawn to any convenient scale; previous to this, however, the largest field and lowest power eyepiece proposed to be used with the telebcope is selected, and the diameter of its field lens measured. In the diagram, S S represents the spéculum, and the short line F F its focal length; upon this line the eyepiece E is supposed to be placed in such a position that the diaphragm is coincident with the line F F. The diameter of the field lens being correctly drawn to ecale, next draw lines A A and В В from the extreme margin of the lens to the margin of the speculum, and these lines will represent the practical working limit of the cone of reflected rays. The next thing to be found is at'what point ought the piano to intersect this cone of rays. This is found by first measuring the semi-diameter of the telescope tube and adding to it the distance beyond its outer side at which the focus is supposed to be thrown. Suppose, for instance, the tube is lOin. diameter, and the focus F F is 8in. distant from the barge tube, the total distance of the focus from the centre of the plane would have to be Bin. This then would be the distance of the centre of the plane С С, from the focal line F F, and the diameter of the cone of rays at the line С С, gives the size required for the actual aperture of the plane. It is of course, advisable to have the plane just a trifle larger than the cone of rays demands to admit of necessary play in its adjustment.
This, I believe, is the most correct rule ; but to those who desire a simpler method I may say that if the plane is l-5th the diameter of the speculum, that will be found sufficiently correct in most cases. As to "C. (I.'s" query respecting the polishing of specula, I may say that, in general, titfulness of movement arises chiefly from irregularity of size in the facets of the polisher, and may be almost entirely overcome by attention to this point. I find the time required to produce а good polish is from three to four hours, but this varies according to the hardness of the glass and the amount of cohesion between it and the polisher to harden. The pitch rosin may be added, or (as Herschel recommends) it may be melted with sutficiont heat to vaporize some of the essential oil which it contains. I find this quite as effectual. W. Pukkiss.
READINGS FROM THE GLOBES.
 Sib,—Geographers have fixed upon the latitude and longitude of a place in order to determine its position upon the terrestrial globe; and astronomers have fixed upon the right ascension and declination of a heavenly body, or upon its latitude and longitude, in order to mark its place upon their maps and celestial globes; but mariners, besides latitude and longitude, require the course which a ship ought to take upon the pathless tracks of the mighty deep, as without correct guidance they may endanger the safety of their vessel. As they make use of the mariner's compass to direct them, it is necessary for them to know upon what points or rhumb-lines they must steer in order to reach their destination ; and consequently the value of accurate knowledge upon these points cannot be too highly estimated. We propose then (1) to define the angle of position between two places upon the earth's surface and the angle of position of a star; (2) to show how to find Buch by forming the triangle upon the globe ; and (3) to point out bow to verify the results by working them out by the proper formal» for this purpose. The angle of position shows the true bearing of one place from another, or the exact direction which the arc of a great circle would take to reach it; and this great circle is represented by the quadrant of the globe ; but it is necessary to bear in mind that it is not the direct course which a ship must steer, for the magnetic needle being of small size as compared with the bulk of the earth, makes equal angles with every' meridian over which it passes. Thus, if a ship were guided by the mariner's compass, according to the true bearing, as found by the angle of position, it would make equal angles with every meridian over which it passed, and would be carried out of its right course, for the quadrant of altitude or great circle does not make equal angles with every meridian over which it passes. If the magnetic needle were sufficiently long, and pointed from one place to the other, the course, as found by the angle of position would be correctly taken; but mariners find it necessary to guide their vessels by the bearing which the mariner's compass gives as calculated by a Mercator'B chart, which is constructed by the parallele of latitude being made at right angles with the meridians; and it is only on the equator, or a meridian pointing north and south, that the angles of
position coincides with the bearing by mariner's compass. They therefore steer their course by what is called a rhumb-line, which cuts all the meridians which it crosses at equal angles, as the magnetic needle does; but the augle of position shows the true bearing of one place from another upon the earth, or the direction which a ship would take if the two places were in sight of each other. The angle of position of a star, which I understand is used in some astronomical calculations, is the angle which that particular star makes with the pole of the ecliptic and the pole of the equator. Thus let P (Fig. 2) be the pole of the equator upon a celestial globe, and P the pole of the ecliptic, and A the star Arcturus; then the angle PAP would bo the angle of position of the star Arctnrus. These angles of position may be determined by the globe approximately; that is, sufficiently near to enable us to compare their results with those which have been worked out by the formula) in trigonometry. If, for instance, we wish to find the angle of position between London and Constantinople, (Fig. 1) we must bring London to the meridian, and having screwed the quadrant over it we must pass its graduated edge over Constantinople, and measure the angle upon the horizon (taking care to have London in the zenith), which will be found to be 104° from the north towards the east. To find the angle of position of Arcturus by the celestial globe, we must bring Arcturus to the zenith, then we can chalk out the triangle or pass the quadrant from Arcturus over the pole of the ecliptic and we shall find the angle on the horizon, viz., 22° We shall then be in a position to пае the formal» to verify onr results; and the formula for this purpose is the same as used to find the shortest distance between any two places, namely, Given the two sides and the included angle to find the other angles. The two sides will be the complements of the latitudes and the included angle the difference of their longitudes, and the angles at the base will be the angles of position of the two places; but to find the angle of position of a star, we have three sides given to find the angle A. The three sides are P A the complement of the declination, P P the obliquity of the ecliptic, P A the colatitude, and the angle may be found by the formula
cosiA = /«■"'■»»_<•
Sin ft sin с
where * denotes half the perimeter of the triangle. Thus in a commercial country like this the study of the globes becomes important, as it gires us elementary ideas of geography and astronomy, by which the mariner may not only know the direction in which one place lies in respect to another, but can tell with precision the precise spot where his ship happens to be.
T. S. H. P.S.—In letter C, p. 372, col. 2, line 12, for A 0 read ВС.
DISSOLVING VIEW PAINTING.
 Sir,—With your kind permission, I propose, in the course of a few weeks, to offer a detailed and practical course of instruction on the higher class dissolving view painting, the result of nine years' experience. It is a fascinating pastime, and the great enjoyment it enables one to afford others is to me its strongest recommendation. To place glass-painting within the reach of those who cannot make their own drawings, printed outlines and photographs are sold for colouring by most opticians. Of these I hope to speak in a suitable place, but I state en panant that nothing surpasses a euperior "hand-painted slide in oils," which will always keep its place in the market, and command its price. I venture to remark, as a nameless one, simply for the encouragement of the earnest-minded, who can bring patience, care, and a moderate amonnt of skill to the work, that when I took up the art, I could but make a modest vignette in tolerable drawing, and only a short time since I disposed of some of my later views (on the Rhine) for ten shillings each. If those interested will kindly follow the directions, Ac., which, by the aid of our invaluable paper, I may give, I think I shall be rewarded by hearing that many have arrived at highly respectable results, while some will have produced "things of beauty that will remain joye for ever." Sahlk.
 Sin,—In reply to N. G. Lamborne, I beg to say that my answers to his queries are the result of
nearly two years' experience in the delightful exercise and pleasure of bicycle riding. As regards learning to ride I accomplished that in about an hour, on an incline of a hundred yards or so. I finit learnt to balance myself on the machine by taking my leg« off the ground and letting the bicycle run down this inclino; I then placed one foot on a treadle and got it into the motion; then the other foot's turn came, and but of all I placed both feet on the treadle. After occasional practice for a day or two I could ride the machine nearly aa well as I do now. I find, like T. Cooke, the best and easiest way to propel the machine ia to place the seat well back on the spring, so that one can give a for ward-down ward push instead of only a downward one. Riding on this plan, I can beat all the riders in my part both in speed and distance, as the motion is not so tiring, 4c., as the other. The twisting abont of the machine from Hide to side of the road, showed that either the rider was not up to his work or that his machine was out of order. I have not found any danger to result from riding a bicycle in narrow roads, and unless a rider should lose his presence of mind, or be unable to manage the machine, I do not think an accident likely to happen. I cannot say, from experience, of the danger or otherwise of jumping on to the saddle when one wishes to mount, but I should think it is u dangerous practice. I should recommend a would-be purchaser to buy a machine of such a height that he could touch tbe ground with his toes when mounted, and he will find it a very great convenience. A good rider never, or very rarely, loses his power over the bicycle. The great secret in turning a corner, 4c, sharply, is "never take your foot off the inside pedal or treadle," or the pressure exerted by the outside foot overcomes the inside, and down you go.
The leg guards, which are generally fitted to bicycles now, effectually prevent all splashing and rubbing of the thighs. "Husband" has given the best mode of taking a bicycle up hill, and like " E. S." I shall believe in ruptures when I feel the effect of them.
 Sir,—1 must apologize for not sending yon the description of my coil La-fore; I do so now, trusting it may not be too late for the several correspondents who were inquiring about it.
In the Exhibition of 1851 there was a large coil by Siemens and Hahtke, made on the vertical principle, which gave extraordinary results, as perhaps some of our readers may remember. This coil was made out of a solid block of ebonite, cut into parallel grooves, into which the secondary wire was wound, the primary being quite detached and slipping into a core in the centre of the coil. Now it occurred to me that it was an unnecessary trouble and expense—which in a large coil would be immense—to cnt these vertical channels out of the solid ebonite, as the tension in each of the compartments, if they were made small, would not be great enough to leap over the interval between each alternate channel; accordingly I proceeded to construct a coil as follows :—I give the size oi my present one ; your readers can alter the ¡size to suit their own several requirements.
I took an ebonite tube about 18in. long, Sim. in the bore, and ¿in. thick ; on each end I cut a screw on the exterior, for about 4in., and on them I fitted two nuts (all ebonite), 5in. in diameter; these nuts form the two ends of the coil, and serve to screw the discs all together, leaving about 8in. of the tube clear at each end—this U very important.
I next cut out about 80 or 90 discs or rings of thin ebonite. No. 20 wire guage, so as to slip on the ebonite tube, and between each disc 1 put a ring of ebonite, about an |in. thick, and the same in depth. Now these discs are not all the same size in diameter. Suppose the distance between the two nuts to be divided into three parts, I make the depth of the discs of the middle division double that of the two ends; this is also important, as the inductive effect of the core is greatest at the centre and nil at the two poles, so that it is desirable to get as much of the wire as possible on the central part of the coil.
Thus then I have 90 discs or thin rings, 60 of which are 4 Jin. external diameter, and 30, G Jin. I have also 90 small rings, fitting the tube, and ¿in. square. I then build up my coil as follows:—I screw on the nut at one end, leaving about 3|in. clear from the end, then I put on a small ring, then a thin disc, then a ring and another disc, and so on, till the whole 90 are thus arranged; taking care,as I said before, that the larger 30 discs occupy the central part of the coil; then I screw on the nut to the other end, and make all tight. I ought to mention that every alternate thin disc has a hole drilled through it, just above the small ring, for the wire to pass through, and I put a small loop of wire in each hole previous to putting them on, м a convenience for palling the wire through; which, without this forethought, is very troublesome to do. On the two ends are screwed two supports to attach the coil to tbe base board.
Now for the winding. Don4 wind in the lathe. I made a temporary stand, and supported the coil on two axes with two handles.—the object of this will be seen presentir. Slip the end of the wire, by means of tho loop before mentioned, through the hole in disc No. 2 (supposing yon to begin at the left hand»; then wind and fill up the ßret channel, the end of which will be the left-hand terminal. Then turn the coil round, join on the wire to the end you pulled through, and fill up the channel No. 2, but irtnd the revene way to No. 1. again reverse the coil, and proceed as before, and so on till all the channels are filled: then solder the outside ends of every alternate pair together. The coil will thus be tilled with a continuous spiral of wire
joined, or connected alternately at the inside and ontaide of each channel. Before winding the wire, took the wire in a boiling mixture of 3 part* of paraffin (eolid) and 1 part white wax—thi» it most important. Perhaps it would be better, though more trouble, to let it pass through the hot solution as yon wind it on. I need the former method.
I think I have clearly explained my plan of construction as regards the secondary wire. I may mention that my primary consists of No. 10 cotton-covered wire, wound in three layere on a bundle of soft iron wires abont ljin. diameter. The wires are elightly insulated by a covering of tape soaked in paraffin and wax, and each layer is also insulated by a few thicknesses of gutta-percha tissue. The whole, when wound, forms a cylinder which will jnst slip into the ebonite tube.
In a coil of this construction it is impossible to break down the insulation if your tube i* a good and tountl one; and the insulation of the wire with the paraffin stops all email leakages, so that yon utilize every part of the induced current, and hence yon reqaire very small battery power. The one that I have described has given good thick sparks of from 8iii. to 4in. in length with one cell of Groves's battery, the platina of which is 2in. by 4in.; and the secondary wire that produces this extraordinary result is, as nearly as I can calculate, about 4 miles.
My condenser is made as follows :—I took about 60 sheets of ordinary good demy paper. I had a sheetiron dish mode, about the size of the paper, in which I heated, by a Bauson's burner, the above-mentioned mixture of paraffin and wax. Into this boiling mixture I dipped each sheet. I find, however, that it cools so quickly that it has not time to drain off; so that there is mnch more than is required. This is easily obviated by holding it before a flro, and it will drain off, leaving, when cold, a beautiful pearly-looking sheet of splendidly insulated paper. And the whole process is so simple and expeditious, not occupying, for the 50 or 60 sheets, about a square foot in area,
The drawing may now be traced, and when the intonaco
more than an hour, or two at the most. I send i small sketch which may make my description some what clearer. I trust that thie description may be of some assistance to your readers. Indoctobium.
P.S.—My thanks are due to "Sigma" for his notice of the air-pump. I wish he would state definitely what vacuum he got with a Tate's pump by the gauge, as I have one which I cannot get to act at all well. I am making one on Newman's plan, the result of which I shall be glad to let your readers know, if interesting. Can any one inform me the best oil to nee with air-pumps, that will not get thick and clog the valves? All that I have tried do so, and thus impair their action.
WALL DECORATION. J-'lj' • ГД7в] Sib,—In reply to "Faber" (1830), the preparation of a wall for fresco painting is a work of time and great carefulness, for on the goodness of the work «lopends in a very great measure the durability of the painting. If the wall is already covered with plaster or laths it ehould be cleared, and the bricks thoroughly scraped and afterwards well chipped. See that the bricks ore in good condition and perfectly dry, and then proceed to lay on the first coat, consisting of river sandand the best old lime, mixed to about the usual thickness. This should be laid on so as to leave a level bnt rongh snrface. At some places on the Continent small flint pebbles are mixed with this comporation to give the requisite roughness. This groundwork shonld be allowed to dry thoronghly; indeed, unless the lime is old, it will be some considerable time before it will be safe to put on the intonaco or painting-surface. This should be prepared with the very best old Urne, perfectly free from grit. An excellent material is prepared from the limestone of Dnrdham Down, Bristol. The lime is mixed in troughs to the consistence of milk, and is then passed through hair sieves into jar», where it is allowed to settle, and
íu^iH " 'tSmaA °a- П U then геайУ t0 bo mixed with the sand (fine quartz sand, well sifted, is the
sand. The implements used to float on the last coat are made of wood or gloss, but trowels of iron may be ?ьТМ^вв 'гот,.ГП91' «* «TM ¡e taken not to press the iron too forcibly on the intonaco. When the Urne
HíñVí « "Ä 1S read* *° Ъе Uid-the ronRh cast must be wetted thoroughly, and the intonaco floated on
«^°Л-а!1Ы with rather more sand than the tirst. The thickness of the two should be about 3-16ths of an inch After these are spread, go over the whole "TM tt TMu °/ wet Unen, which will remove the marta <я the trowel, and prevent the surface being too smooth I
Now that we have eliminated one of the supposed
from the unexhausted parts will be developed more than those having the old developer continually passing to and fro over their surface. This I am disposed to think is the cause of the increased line of light on the sun's disc as represented by the American photographs. In order to obviate this defect, I would suggest that the plate be moved about as little as possible, or the solution be poured on and off—first from one end nnd then the other—or by developing in a bath. The latter, at first sight, would seem the most promising, as it would give a free supply of developer, and that too of more uniform strength over the whole surface than can be obtained by the usual method.
Our English operators will do well to see to these matters before the next expedition sots out on its journey, and be certain that all has been done that can be done to remedy these defects, and lot us see, on its retara, that its photographic operations have been at least equal to the Americans', if not superior to them, if that is possible.
_ Those interested, and requiring more minute purticulars, will find the subject fully discussed in the following papers, to which I have had the honour of communicating my views from time to time -—The Photographie Journal, Nos. 108 and 110; The Britieh Journal of Photograph), Nos. 140, 226, 233, 239, 426, 431, and 400; The Itluitrated Photographer, Nos. 22, 25, 28,32, and 50. G. Marlow.
ACCIDENTS OF THE WORKSHOP.' П7Э] Sin,—As the Brituh and Foreign Mechanic is now amalgamated with the English Mechanic I send you the continuation of this subject, which was commenced in the first named journal on July 2, p. 842. It may bo as well to give a short résumé of the contents of the previous part. The mechanic, always in the midst of moving machinery or climbing scaffolding many feet from the ground, is continually liable to accidents, and a knowledge of what to do, and what not to do, will be found of very great nse. In the first place, where the accident is apparently serions, the clothes of the injured man should be loosened, and he ehould be laid on a door, or shutter, or a plank. An attempt should be made to discover whether any bones are broken, and if there is profuse bleeding it should be arrested immediately. Where there is a cut or gash, if the blood is scarlet and comes in throbs or jnmps we know that it is arterial blood, i. е., comes/ron the heart; bleeding of this kind is stopped by tying a ligature (a narrow etrip of linen) between the wound and the heart. But if the vital fluid is of a dark colour, and flows steadily in a stream it is venous blood, and is going back to the heart ; in this case the ligatnre ehould be tied or pressure applied between the extremity of the limb and the wound. After the wonnd has been well washed, a compress of a pyramidal form made of linen rags or lint should be applied, apex downwards, and bound firmly round with a bandage. Before applying the bandage it should be saturated with water, or a little simple ointment placed on the part next the wound. If the gash is long a stitch or two should be passed through the edges with a bent needle and silk,— each etitch tied separately. H the bleeding of the artery be stopped by the pressure of the finger or the ligatnre, the compress may be dispensed with, and а piece of lint folded three or four times placed over the wound and bound down with a bandage. It the wound is of such a nature that pressure will not arrest bleeding, especially where one or more of the arteries of some magnitude have been severed, more forcible means mnst in these cases be applied; the offending artery mnst be sought for, and when found drawn out by means of what is called a tenaculum, which resembles a shocmaker'e sewing awl ; when this is not at hand a large pin bent, or a pair of tweezers with fine points; may be need. When the artery is pulled forward it should be tied with some thread two or three times double, and if there are others they shonld be treated in a similar manner. It mnst be observed that the extremity of the divided artery nearest the heart should be secured. After the blood vessels have been tied the wound should be washed, if caused by an instrument covered with foreign matter, or if not it is always well to cleanse it; but allow as little water as possible to enter the opening, for it has a tendency to swell the flesh and increase the gaping, especially if warm water is used. Any piece of glass or dirt may be removed by a dry éponge. When cleansed the edges are to be brought together with a few stitches or adhesive plaster, and a bandage bound round in the ordinary way. This should be removed doily to see whether the wound is inclined to slongh or discharge matter; when such is the case what is called the " water dressing " should be resorted to—this is merely the bandage or rag covering the part to be kept saturated with water. In some cases "proud flesh "may form ; then, as in sloughing, a little nitrate of mercury ointment may be applied. It is best, on the whole, not to meddle with the dressed wonnd more than to keep it clean, which is a great thing, for it mnst be borne in mind that the best healing doctor in the world is nature, she can and does perform what no human being can or ever will, and the surgeon's motto is to assist and not interfere or interrupt nature. When it is found that the edges have adhered to each other the stitches may be removed, also the bandage, and a little simple ointment applied on some lint or linen rag, which will prevent the part being injured by dust and other irritating matter, and assist in healing the wonnd by excluding the air. The cause of wounds being irritated and prevented from healing through not being excluded from the air is from the fact that the atmosphere is impregnated by millions
* The right of translation and reproduction reserved by the writer.
of minute invisiblo animalcula which is во elaborately explained in Professor Tyndall's lecture on "Dust," which I should advise all my readare to obtain. This «maní has demonstrated beyond all reasonable doubt that were it possible for all the air we breathe to pass through a filter of cotton wool before entering our lungs that life would be prolonged many years. In proof of this observe the advanced age to which farm labourers live to what those do who are living in the foul air of our great cities. But I am going from my subject, though I could write many pages on what I have just alluded to, but it would be turning from the path upon which I have set out.
Other means are to be adopted when the hemorrhage is obstinate, such as the application of ice or very cold water to the part. Cold is one of the best stiptics we have, and seldom fails to do good; it not only contracts tho gaping mouths of the arteries but also those of the wounds, thereby arresting bleeding. The ice can be applied directly to the wound, if clean, or be wrapped in flannel or a piece of linen rag, and on the cessation of the flow the wound bandaged as before directed.
Cases have been known where the artery has only been partially severed; in such instances contraction is impossible; therefore it is necessary to complete the division with a lancet. This should be left for a medical man to do, for it is an operation that requires a knowledge of the venal and arterial system. It should on no account be attempted by a novice, unless medical aid is nnprocurable, and this appears the last resource to save the person's life by stopping the bleeding. This is founded on the known tendency of arteries to self-contract on division. The danger in this operation is that an inexperienced hand may, instead of completing the division in the already wounded vessel, injure others in the act, and so, in trying to do good do a great deal of harm, and make matters worse than before. The safest and surest mode of arresting hemorrhage, when the wound is of some magnitude, is by tying the blood-vessels; this, when effectually done, is unsurpassed by any other means relating to external bleeding. It should be borne in mind, that all the arteries must be secured, else bleeding may proceed after bandaging, and the patient unconsciously lose an alarming amount of blood.
In my next letter I shall speak of internal hemorrhage. Frederic J. M. Butt.
which a given or known volume may be abstracted for the special determination.
The chlorine, sulphuric, and carbonic acids may be thus determined, as also the amount of hydrate in the free state.
From the result of this analysis, we calculate the percentage composition of the liquor, and having that knowledge, we may readily form an idea of the quantity of raiuttc toda or crystallized carbonato which may be obtained from it.
Theoretically, 62 parts of anhydrons soda should produce 106 parts of anhydrous carbonate, 286 of crystallized earbonate, or 80 parts of the hydrate. 80 parts of the hydrate would of course in its turn form the same quantities ; but if it only contained 60 per cent, of the hydrate, the quantities obtained would be 8-5the of the above—Ariz., 036 of anhydrous carbonate, 171-6 of the crystals, and would only correspond to37-2 parts per 62 of anhydrous soda (NajO).
George E. Davis.
THE SUN'S PARALLAX.  But, —Allow me to say a few words in answer to " Veritas's " letter on page 425. It is evident that if the data of a calculation be correct, and the reasoning false, the result must necessarily he incorrect. Now, in my letter, on page 402,I wished merely to point out the false reasoning, and correct the error of "Veritas." And if we assume the data given by him on page 228 to be those " which are generally accepted to be terms," it is plain that the parallax found by him in the same letter cannot be " that which is generally accepted to be true," because the reasoning is false. For aught that I know, not being an astronomer, the parallax may be correct, but if so, the data cannot be. Surely " Veritas " does not want ¿gurus to enable him to see" this? Hm¡o.
WEIGHTS OF CHEMICAL SOLUTIONS. 1179] Sib,—I am afraid I cannot be of much use to "Alkali," as regards finding the amount of pure anhydrous soda from the density of the black ash solution; probably other readers may contribute what he requires. If the solution contained nothing but pure caustic soda, the percentage might he approximativcly determined by the use of Dalton's table.
To use Dalton's table the specific gravity must be known ; and this is calculated by multiplying Twaddell's degrees by 5, and adding the resulta to 1000 :— 80° Twaddoll x 5 = 400 1000
1400 = specific gravity, or by substracting Beaumé's degrees from 144 and then dividing the same number by the result :—
^Beaume Ш _ ^^
When tho specific gravity is found, reference to Dalton's table will show the percentage ; but to avoid any calculation, I have worked out the table, showing Beaume's degrees with Twaddell's, and also the real specific gravity.
Percentage of sodium oxide (NajO) in solutions of the hydrate.
The above will probably not be of much use to "Alkali ;" I merely give it, thinking it may be of some use to the few of your readers—saving them the trouble of calculation, &c.
"Alkali " must remember too, that the above table is for the percentage of soda when present in solution as a hydrate, and not as a carbonate; in which latter state it is present in black tun mixed with sulphate, sulphite, or sulphide, either separately or together, with a little hydrate and some undecomposed aalt; it will therefore be seen that the table is useless for the estimation of the carbonate when it is present in solution.
I ho only cowect method by which the exact composition of the liquor may be known is by an analysis; this may be either gravimetric or volumetric; the latter is preferable in this case.
The filtered liquid is diluted to a given volume, from
LATHE CONSTRUCTION.  Sib,—lam sorry not to be able to comply with the wish of "H. D. C, Capt. R.E." (letter No. 1381, as I am not in the least an ornamental turner, and I have already written one letter to yon (see p. 833 of the current volume) on this very subject. Had I the inclination and could I afford the time to do it, I have the kindest invitation from the gentleman at Halifax, who supplied tho photograph of the cutting engine (p. 12), to go to visit him and make drawings of all his apparatus. I do not believe that there is a better shopful of tools in the world than his, for they were not bought at a sale nor ordered wholesale from a maker either, but made consecutively to drawings and directions given by their possessor to a workman who yields to none for accuracy in putting his work together, commencing about October, 1846, when I saw the first pieces of his lathe in hand. As it is, however, I cannot undertake to go down to Yorkshire and spend a week making drawings and putting together again all the things I should have to take to pieces. Had I fancied fancy work, I should have done SO long ago. If the R.E. Captain is stationed at Chatham, I may in my capacity of Engineer-Volunteer officer, have the pleasure of being in his company at the Field Works Inspection there on an early day, and shall be glad to discourse on the subject of lathe work.
J. K. P.
 Sm,-- While thanking "F. R.A.S." for his reply, it being hardly an answer to my question, may I observe that it is scarcely what I require ? I hope that I may consider myself sufficient of a mathematician to understand, at least, the rudiments of conic sections.
What I wished was for your correspondent to decide if the definition I gave was correct, as, a dispute having arisen at a recent meeting of the Mathematical Society that is based on it, I was asked to get it decided. The point, therefore, is, Is the definition I gave rigidly correct?
Also, tho vertical plane of a conic section is the plane passing through the vertex and parallel to the plane of the conic section.
That the circle is a conic section is of course indisputable, but if it may be regarded scientifically as an ellipse the definition of De Morgan, that all ellipses have two foci and a minor and major axis, will be apparently incorrect.
At the same time I must thank Mr. Proctor for his opinion, and I presume he regards the conic section produced by a plane passing through the vertex of the cone a hyperbola, with its curves passing through its centre, and having only one principal vertex, and with its asymptotes identical with the sides of the conic section.
Otherwise a piano diverging from the slant side of a cone, and cutting the cone, will not be a hyperbola, if it cut the vertex of the cone.
a UR8/E MrsoRis.
 Sib,—I shall have very much pleasure in acceding to the request of "An Axinouth Resident" (see letter 124), and will with your permission, provided no other correspondent volunteer in the interim, commence a series of articles on "The Microscope ; How to Choose and How to Use It," in tho course of a few weeks, say about the third week in August.
As regards mounting in Canada balsam, your correspondent finds, as have all mounters, that air bubbles are a plague and a vexation. If the balsam be tolerably fluid he has only to keep his slides for a few days at about 70 deg. to 80 deg. of Fahr., and the bubbles
= 14489-216 = weight of cone А С II
8-1416 x 440
.-. 12 + x = МЫ
.-. x = 4-54
Again, AR + R В : С S :: AR : BR
.-. 12 + 4-54 : С S :: 13 : 1
.-. С S = -33- = 1-378
Hence C H = 2756 = diameter of section,
GAS BY A NEW PROCESS.  Sib,—I hare copied the following from the ТЫа newspaper, a few years ago. I forward it to you with the hope that some one (or more) out of the numbers of readers, of our Mechanic can manufacture, an apparatus of the kind, and also understand the process of the manufacture of the gas afterwards. If there could be found among the many readers who could and would do this, I am sure of this he would get an immense custom, and it would be a boon to numbers—your humble servant for one.
"Gas By A New Process—An experiment in gas lighting, by Count ie Val Marino, was made yesterday evening on a piece of ground at the back of Fetterlane. A small gasometer was erected which was connected by tubes to a furnace, containing three retorta, one of which was partly filled with water; the second with tar; and both being decomposed in the third retort, formed the sole materials from which the gas was produced. The process appeared to be extremely simple ; and the novelty of the experiment consisted in the fact that the water and tar were the only materials employed, though the inventor says that any kind of bitumen or fatty matter would answer the purpose equally well. After the lapse of about half an hour after the commencement of the process the gas was turned into the burners, and a pure and powerful light was produced, perfectly free from smoke and anpleasant smell. The great advantages of this kind over that produced from ooals consists, it is said, in the cheapness of its producing materials, the facility with which it ie manufactured, and the perfection to which it is at once brought without the necessity of its undergoing the tedious and expensive process of condensation and purification, for in this instance as soon as the preliminaries were completed, the light was produced in a perfect state within a few feet of the gasometer which, although of inferior size, was said to be capable of affording light for at least 50Ü lamps or burners. The price is estimated not more than one-third that of coal-gas, equally available for domestic use, and such that small gasometers might, at a trifling expense, bo fitted up at the back of gratos in private dwellings, from which tho gas could be conveyed in India-rubber bags to any part of the house, thereby preventing the many accidents which occur by the use of tubes or pipes."
I do hope we shall hear from some of the readers of our Mechanic that they will at once undertake tho manufacture of the apparatus, and for trilling royalty instruct any person in the process and manufacture of the gas. J»hn Fleet.