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error, which is called the error of the tables, must neces-(employing dashes to distinguish the particular results)
sarily be a function of all the elements that enter into we shall derive by the ordinary methods of elimination,
We computation of the planet's place, which we will
call, and if we denote the elements of the orbit by x,
,, the equation must take the form

e ax + by + cz, &c.

Another observation will give

e' = ax + by + c'z, &c.

☛ = a′ x + b^ y + c" z, &c.

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| which, being inverted, give the required weights, which we will denote by pz, py, and pe In order to find the moun error of y, and z, we must take the sum of the squares of the residual errors that we have already determined. The squares will be respectively and there will be as many equations as there are ob-0-0620, 00046, 0-0090, and 0.0048, the sum of which is servations Now, there can be at the most, in a pro- equal to 0:0804, the square root of which is 0-284 blem similar to that that we are considering, seven The mean errors of x, y, and z are given by the formul unknown and therefore seven observations would be sufficient to determine the corrections to the elements. z = — similarly for y and x, mutatis mutandis. But each observation is effected by an error, or rather numerous errors, arising from accidental causes, and which cannot be subjected to computation, such as tremors of the instrument from wind, errors in refraction produced by changes in the temperature of the atmosphere, which will also produce anomalous changes in the parts of an instrument, and above all by imperfection of the senses, and an incapacity in the observer to estimate very small intervals of time and space. The only method of removing these errors is to multiply the number of observations, when it is assumed that all small accidental errors will destroy one another. But to increase the number of observations is to increase the number of equations of condition, and hence arises the necessity of inventing a method of solution in which each equation shall equally participate, and of derizing a result that shall be as little affected as possible by error, and if possible to determine the amount of probable error in the result. Squaring each of the equations of condition, ard taking the sum, we shall have an equation of the following form:

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SIR,-As regards the letter of "J. T." page 14, respecting "Violin Varnish," I quite agree with what he says. The information which he desires would be acceptable to many of your readers. I have myself, z (a2 + œ2 + &c.) + y (a b + a' b' + &c.) +z (a cat the present moment, a valuable Italian instrument, on which I have played for more than 20 years, but its belly is without varnish. The cause of this is as follows:-I purchased the instrument, at a high figure, at the sale of an eminent violinist's effects, and by imagining that another coat of varnish would improve the tone of the old violin. I made and applied a var nish of naphtha and shellac, but the result very much disappointed me, for he sound was somewhat deadened, although the alluring sweetness of tone

Hence we have the following rule to form the equation
that gives a minimum for any one of the unknown
quantities: Multiply each equation of condition by the
coefficient of the unknown quantity in that equation,
taken with its proper sign, and then add together ali
these products; and this being repeated for each
unknown quantity, there must result the same number
of equations as unknown quantities, whence each is
reduced by ordinary algebraical operations.
We give as a numerical example the following
equations that are given by Gauss, and have been
employed ever since as an example:-

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becomes instead of zero. This
is termed
the residual error; and if a result be deduced from
any three equations, the fourth will not be satis-
fied, but leave a small error. We must use the rule
given above for the normal equation of z, multiply
each equation by 1, 3, 4, and - -1, and take the sum, for
y, it will be necessary to multiply each equation by
1, 2, 1, 3, and add the results similarly for z, we
shall have, then,

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The solution by ordinary methods gives,
x = 2.470, y = 3.551, and z = 1916

If these values be substituted in the original equations,
it will be found that no one equation is accurately
satisfied, the residuals being

-0-249,- 0068, + 0·095, — 0:069.

To determine the probable error of each unknown is a rather long and intricate computation: we indicate only the method here, the proof of what is inadmissible. In the first normal equation write-1 for the absolute term, and in the other equations zero, for each of the absolute terms: the value of a then found from these equations will be the reciprocal of the weight of the value of found by the general elimination; similarly for the other unknowns. Writing then,

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remained.

In a few weeks I decermined to scrape off the var-
nish, and did so carefully with a piece of glass, but
unfortunately the first coat of varnish came off with
the second, and the belly of the violiu has, since that
time, remained bare, for I have been afraid of again
meddling with it. I keep the instrument in a silk bag
in a mahogany case, and thus the air does not appear
to affect it. Notwithstanding this, I should, of
course, be highly pleased if I could restore it to its
original appearance.
cannot venture to apply any of them, neither would
I know there are many "Violin Varnishes," but I
place it in the hands of a violin maker until a suit
able spirit varnish like the Italian varnish spoken of
by M. Grivel), has been tried and approved. It is
strange, and I have often thought so, that neither
Rode nor Louis Spohr, the latter of whom has touched
of all instruments, has said anything in reference to
upon almost everything connected with the greatest
the varnish.

I

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rather small, and if designing such a cylinder with equal piston speed, I should give a steam port of 28 or 29 square inches area, but such as it is it will do very well. There are worse things by a great deal about this engine than the proportions of its steam ports, as we shall see by-and-bye.

The steam is cut off from the high pressure cylinder at 34 per cent. of the stroke, or 144in., and the diameter of the cylinder being 16in., we have a space of 165 cubic feet to be filled twice every stroke, or 3:30 cubie feet per revolution of the crank shaft; this at 60 revolutions per minute is equal to 198 cubic feet, or 11880 per hour, to which we may add one-fourth for waste in filling ports, piston clearance, leakage and cooling, and we have 14850 cubic feet of steam required per hour; this at 60lb. per square inch above the atmosphere, or 751b. total pressure above a vacuum, requires for its formation 39 cubic feet of water, but the boiler is capable of evaporating 50 cubic feet per hour, se there can be no question of its sumciency.

We will now take a look at the proportions of the slide valves, and see how they acquit themselves in the performance of their duty of distributing the steam to the cylinders, but before I do so I shall just state what are the proper proportions and essential conditions of a good compound steam engine as far as its valve gear is concerned.

The valve which admits the steam from the boiler to the high pressure cylinder should be capable of cutting off at any point, from, say, 10 to 95 per cent, of the stroke, and of detaining the expanding steam in the cylinder to do duty on the piston to nearly the end of the stroke, and this valve should, if possible, be placed under the direct control of the governor. sure cylinders should be free and unrestricted from The communication between the high and low presthe beginning to very near the end of the stroke, in order that no illegitimate or unnecessary back pressure may exist to retard the motion of the high pres sure piston, and that the low pressure piston may receive the full benefit of the unrestricted expansion of the steam contained between the two pistons. The communication between the low pressure cylinder and the condenser should also be freely open from the beginning to nearly the end of the stroke, in order that its piston may continue to receive the benefit of the vacuum as long as possible. "Relivot's" high pressure valve has 7 in. of travel,

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valve and those of the ports are equidistant; with
these proportions this valve cuts off the steam at 34.
per cent. of the piston's stroke, or 14-25in., and ex-
hausts at 78 per cent., or 32-75in., and at the same in-
stant compression begins on the other side of the
piston. The valve of the low pressure cylinder also
has 73in. of travel, 2-in. of lap, and in, of lead, and
the exhaust edges of the valve and ports are equidis-
tant; these proportions cause it to cut off the commu-
nication with the high pressure cylinder at 36 per
cent., or 15 12in., and to exhaust at 78 per cent., or
32-75in., exhaustion ceasing and compression begin-
piston.
ning at the same instant on the other side of the

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at once become apparent, and are plainly illustrated in the annexed sketch, Fig. 1, in which I have placed the cylinders side by side, and attached their piston rods to the same cross-head, so that they make their strokes simultaneously.

Now two serious evils due to this early exhaust

«Relivot's" engine or not, but that is of no importI do not know whether this is the arrangement of ance, as it does not affect this discussion in the least, and moreover it is a common way of constructing compound engines.

The cylinders are drawn to a scale of half-inch to the foot, but the valves and ports, for sake of greater distinctness, are exaggerated to the inch scale. The pistons in both cylinders are at the point when exhaustion takes place, viz., 78 per cent. of the stroke, and they are moving in the direction of the arrows,, and both valves are at the middle of their excursion, just closing the exhaust on one side, and opening it SIP, So long ago as October last year, in the numon the other side of their respective pistons. The ber for the 22nd of that month, on page 140, Rel- steam from end A of the high pressure cylinder is, ivot" gave some of the dimensions of his compound passing away into the conuesting pipe and valve engine and boiler, and solicited the opinions of chest of the low pressure cylinder, thus undergoing "practical engineers considerable expansion and reduction of pressure at upon the same. I replied, asking him to send more particulars, and promising the cylinder, and driving the piston at least 19 per the very time when it should be securely bottled up in to give him the information he required. He gave the required dimensions in the number for November 19th, on page 242, and I at once set about writing this letter, but I laid it by for reasons I need not trouble you with, and did not resume it till now. I hope it is

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cent. further on its way to the end of its stroke. At the same instant that the steam is thus recklessly permitted to escape from the positive side of the piston A, compression be gins on the negative side B for it will be seen from the position of the valve. that exhaustion from that side has just been interWith your permission I will just recapitulate his cepted; the piston, therefore, during the remainder questions here. First, "Will the boiler supply those of its stroke encounters a great resistance in gradually engines with steam? Second, "Are the areas of compressing the unexhausted vapour back into the pistons, and ports, and travel of valves, properly pro-port and small space allowed for piston clearance. To portioned?"; and after stating in his last letter, be sure, a part (and only a part) of this power is reThat those engines are working in connection with stored to the piston on its return stroke by the re-exa water wheel," and that "their load is varying from pansion of this compressed vapour. But why comday to day," he asks "Would an independent cut off press it at all? The evil resulting from doing so can valve be advisable?" The dimensions of his boiler be avoided by using a properly-constructed valve are-"Shell 30ft. long, 7ft. diameter, containing two motion. furnace flues, 2' 7" diameter, with grates 7ft. long." This boiler is capable of evaporating about 50 cubic feet of water per hour, with good coal and sharp draft, and the steam from that quantity of water if used in a well-constructed condensing engine, cutting off at about one-third of the stroke, will produce about 100 to 120, or perhaps more, indicator horse power.

The stroke of the high pressure cylinder is 42in., or 7ft. for the double stroke, and it makes 60 strokes per minute, or 420ft. per minute piston speed, and the diameter of the cylinder is 16in. The steam port is 11in. long, and 18in. wide, or 15 square inches, which is very good proportion. The speed of the low pressure piston is the same as the high pressure one, and

At the same time that the above bad work is going on in the high pressure cylinder, similar bad management and prodigal waste are going on in the low pressure one, for the steam, which up to this instant has been driving the piston on its way, is suffered to escape. to the condenser from end C, instead of being kept on the piston at least 19 per cent. longer, and compression also takes place on the other side D, as in the high pressure cylinder, for the communication of this end of the cylinder with the condenser is prematurely cut off, and the vacuum applied to the wrong side of the piston.

But I have yet to point out the greatest evil resulting from the bad proportions of these valves, which is

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and as four catch the wind, the total aperture is over 1400 square feet. The sails are 12 x 8, and five together présent a surface of more than 400 square feet. The difficulty of getting the sails back is entirely obviated by their being enclosed in the windcap, because the building presents such an obstacle that in a strong

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o be found in the restriction of communication between the two cylinders.

I have said at the beginning of this letter that one of the essential conditions of a good compound engine is" that the communication between the two cylinders should be free and unrestricted from the beginning to the end of the stroke," but how do we find it in this case?

The valve of the low pressure cylinder cuts off at 36 per cent. of the stroke, that is to say, the communication between the two cylinders is improperly intercepted at that point, see Fig. 2, which shows the position of the several parts at that instant. The low pressure valve F has just closed, and no more steam can pass from the exhausting end B of the high pressure cylinder to what should be the receiving end C of the low pressure one. The high pressure piston has to spend its energies in cramming the unexhausted steam into the passage of communication and valve chest of the low pressure cylinder. The 36 per cent. of steam which has gained admission to the low pressure cylinder makes a faint effort to drive the piston by its expansion. It is but a faint effort compared with what it should be, for it is unsupported by the great body of steam which should have free ingress to its assistance, but from which it is cut off-isolated-by the premature closing of the valve.

If that engine were mine I should make the following alterations in it :

I would make the ports in both valve chests exactly alike in their transverse dimensions, that is to say, I would cut in. off each of the admission edges of the ports in the high pressure one, and fin. off each of the exhaust edges of the ports in the low pressure one. I

SIR,-In reading over "F.R.A.S.'s" letter, it gave
me great satisfaction to hear him speak so well of Mr.
Wray's object glasses, as I have a 4in which I got
from him. On Jan. 24th, 1869, I had the pleasure of
observing three occultations of the stars 115, 119, and
clear until they disappeared behind the moon.
120, in Tauri. These stars were quite bright and
July I had some good views of Saturn, although he
Venus has shown very sharp,
1870, and on March 5th,
so much so that some of my friends thought it was
the moon that they were looking at. On Jan. 25th,
six stars in the trapezium of Orion, and two small
had the pleasure of seeing

would then cut 2-in. off each of the admission edges of the low pressure valve, which would leave it in. of lap, and I would make its exhaust edges 7in. apart, or the same as the exhaust edges of the ports, and I would then reduce the travel of the valves from 7in., as at present, to 5in., by putting on a new eccentric, which should drive both valves, and this eccentric should be set to give the valves in. of lead. I would do away with the present high pressure valve, and introduce a compound valve, as shown at Fig. 3, which consists of three pieces, viz., slide valves G and H, and an interposed plate I. The valve H should be worked direct from the eccentric by rod J. This valve is made with an exhaust cavity K, whose edges are equidistant with those of the ports, and two admission passages L L' straight through its solid ends; the admission edges of this valve have of lap, the same as the valve of the low pressure cylinder, and of course the same lead. The interposed plate I has two ports cut through it exactly opposite the steam ports in the cylinder face, and of the same dimensions; this plate dies loosely upon the back of valve H, and valve G lies loosely upon the back of I, and all three are pressed up together by the steam. I is prevented moving from its proper position by studs or stoppers fixed to the sides of the valve chest. Valve G is a plain solid plate, having in. of lap at each end beyond the ports in plate I; this valve is worked by a "link" M, one end of which derives its motion from a rod N, pinned to the main eccentric rod at O, and the other end is worked by a rod P, from a small eccentric Q, fixed on the shaft beside the main eccentric. Q has 24in. of "throw," and it is keyed on the shaft with its centre line, making an angle of 158° with the crank (I am now speaking of a horizontal engine). The effects of this construction are-that when link M is lowered so as to bring eccentric rod N into line with valve rod R, the movements of valves H and G will be very nearly simultaneous, and steam will not be cut off till the piston has performed 95 per cent. of its stroke, and exhaustion will take place at 97 per cent. But wben the link is moved from this position, simultaneous action of the valves ceases, and the movements of valve G become in anticipation of those of valve H, and this anticipation increases gradually till eccentric rod P is placed in line with valve rod R, when steam will be cut off at 10 per cent. of the stroke, or 24in., and any amount of admission between these extremes is to be found between these two extreme positions of the link

stars a little below in the nebulæ.

Since I have read "F. R. A.S.'s letter," I must acknowledge that I am proud to be the owner of such an instrument. I think that I was the first who made mention of Mr. Wray's object glasses in the ENGLISH MECHANIC, Some time ago; and as an act of gratitude to Mr. Wray I cannot refrain from writing, as his name is now before the readers of the ENGLISH MECHANIC. If not trespassing too much, I wish to say a few words of encouragement to my fellow working men. When I first made a start, 25. was all that I could spare for an object glass, and no ENGLISH MECHANIC to help me on-no "Chats on the Stars." 1 had not the privilege that the working men have now of getting every question answered through the columns of the ENGLISH MECHANIC; but perseverance has done more for me than money could ever have done; and now that I have overcome the difficulties that I have had to contend with, and am in possessionof a good telescope, I do not wish to put it under a bushel, but I am ever ready to bring it out to any one that can make it convenient to call on me. Working men, think of this; and let your motto be Nil desperandum, D. ALSTON, Clyde-street, Merefield, Rochdale.

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side, which acts as an exhaust, so that nearly the wind there will always be a partial vacuum on the lee whole of the concentrated blast is available for work. The mill-house must be, of course, a substantial brick building, either square or round, according to fancy. The windeap above may be of thin board, but the joisting must be strong, in order to stand the strain of the upper gudgeon.

The

The regulation is a very simple matter, because the out by hand gear round the main shaft, or better, twelve sails are on rollers, which can be reefed er let perhaps, by means of a self-acting governor. pressure of a good working wind of 20 or 30 miles an hour is found to be from 3 to 4lbs per square foot, or at least at double that upon the sails. HENRY W. REVELEY, Reading.

PHRENOLOGY AND BIG HEADS. SIR,-Having for many years taken great interest in the study of phrenology, I beg you will allow me to say a few words in reply to some of your correspondents, who have, through great ignorance, endeavoured to throw discredit and ridicule on the science. It is a great mistake to say that phrenologists assert that big heads have always the most power. All true phrenologists maintain simply that size is a measure of power, with this reserve-viz., all other things being equal, and they will invariably maintain that temperament or the quality of the brain is most essential to the effective working of the organs; therefore an averaged-sized head with well-proportioned organs aud an active mental temperament will produce far greater and better results than a large head with ill-balanced organs and a slow lymphatic temperament.

THE HORIZONTAL WINDMILL. tion a plan for this purpose, on a scale of 1-12th, and many years' experience. I know a man who has SIR,-I take the liberty of sending yon for publica- I make this statement from personal knowledge capable of doing real work, and suitable for driving a head 23in. in circumference which, by the way, is a two pair of usual 4ft. stones-or, say, three, as one very large size-and although he has had many may be frequently up for repair. enclosed in a windcap, because the open horizontal and on the other hand, I know a man with a head The sails are advantages, has produced little either good or great; windmill cannot produce profitable work, on account only 214in., but the preponderance of brain being in of the wind only catching one sail at a time, and that the upper region, and with a most remarkably active for an instant only, besides the insuperable difficulty mental temperament, who has taken a most prominent of getting the sail frames back against the wind; part in the political and literary world. whereas in the common vertical windmill all the sails act at the same time, and moving edge on, atmospheric friction is very slight.

five sails are always acted upon by wind concentrated
In the horizontal enclosed form it will be seen that
by the funnel-like openings. The latter are 24 x 15,

acquainted with the subject, that temperament is, in
I may observe, for the information of those little
believe, invariably big heads or remarkably active
breeding is to the horse.
regard to the human brain, much the same as blood or
Self-made men have, I
temperament.
S. H. A.

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DIE

BENNETT'S CHUCK.

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16

SIR-In compliance with "Kennington Amateur's" request, I send drawing of Bennett's chuck. Fig. I shows front view, with work 1 diameter, the greatest the chuck will take in. Fig. 3 shows the internal sliding pieces taken out, and the steel die in its place, grasping a small wire. Fig. 4 shows the die turned the other way up for a bar from to diameter. Fig 2 is a plan view. The inner, faces of the sliding pieces are lined with steel plates the nibs at the upper corners being sawn into some distance, and slightly bent downwards, so as to grasp the corners of the die to prevent it falling out. The alider moves strictly across the centre, and when the acrew is tightened by means of a square-ended screwdriver, with a very large powerful handle, the slider sets fast in its groove, partly by the oblique pressure of the work or the die, and partly by that of the thread of the screw. There is a small spiral spring let ball into each of the sliding pieces, at the lower end, to keep them steady, and prevent their falling out, and a flat steel ring, held on by 4 screws, protects the hands. I believe it is a very good chuck, and the reason I do not like the one I made is, that it is got so well fitted as it ought to be. It was invented by Mr. Bennett, one of Mr Evans' workmen, and is in common use in that establishment. I think usually they are made with a large screw at back, so as to go on to a plate chuck, instead of screwing direct on to the nose of the mandrel itself. J. K. P.

THE IMPROVEMENT OF OLD COTTAGE AND

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CABINET PIANOFORTES.

SFR, Although many valuable improvements, especially in the action, &c., of old upright cabinet or cottage pianos may be carried out, to the great improvement of both touch and tone, it is obvious that no great augmentation of the power of the latter can be got without resorting to the use of either more or thicker strings, which usually necessitates employing some means to do what, in many instances, would greatly benefit their owners also, viz., to "strengthen their backs."

In a former series of papers on this subject, written by me, one of which was printed in No. 239, Vol. IX., I mentioned a very effective method of doing this in new instruments, employed by Messrs. Rolfe about A.D. 1854, for which Mr MolyBeaux afterwards solieited a patent, which patent was not completed. In this plan, each wooden bracing is grooved to admit the central web of a T iron bar; of course this may be done to an old piany, but it is done much more easily before the bracings are fixed in their places; so, instead of doing it to an old piano, I would suggest the following method of forming grooves or recesses for the T orangle iron, which. instead of weakening the original bracing ads considerably to the total strength of the instrument.

To form these recesses conveniently, I would insert additional wooden braces between the original ones, leaving from in. to fin. space between them, according to the thickness of the angle iron which is to be inserted. These additional wooden braces ought to be well fitted against the back of the wrest plank, so as to form a sound joint when glued, also under the wrest plank if shouldered on. Should the belly bars be in the way of the additional bracings, they may either be grooved to admit the belly bars, or, what I think preferable, two pieces of wood, of the required. section, inay be glued and nailed on the front surface of each brace, leaving a groove or recess between them to admit the belly bar. As it would be difficult to fit each brace so that it shall bear firmly under the wrest plank and on the bottom, I would recommend to cut them about in. too short, also about in. shorter at back than front, and to form a perfect joint between the brace and the bottom, by driving in a hard wood wedge, having first secured a cleat on the bottom (in front of the brace), so that the latter cannot be forced forward against the belly by the act of driving in the wedge.

The new bracings will of course be secured to the wrest plank at top. Lot only by glue, but also by a strong screw, or what is preferable, a screw bolt and nut, bearing against a large washer; the hole for this bolt should be bored 1-16th inch large, so that it may not act as a dowel, and prevent the wedge from forcing the shoulder of the brace up against the under edge of the wrest plank; this bolt also forms an excellent clam to press the glued surfaces together, which is an important consideration when the work has to be done by an amateur, or by a workman who has not plenty of iron clamps at hand. It is obvious the recesses thus formed between the bracings are capable of receiving either the central webb of a bar of T iron, or one of the members of a bar of ordinary L. or angle iron. The latter is now kept in stock by Messrs. Moser and Sons-and by no other London firm I know of-of very suitable sections, say 2 x 1 x 1, or 3 x 12 x 5-16th. From three

to five such bars as these, securely bolted through the wrest plank at their upper, and through the bottom at their lower ends, would "strengthen the back of any sound well-made cabinet or cottage piano. There are many thousands sucb, male within the last thirty or forty years, which are much too good to be allowed to perish and "go to the fire," as if they were of no more value than ancient human animals-sufficiently not only to enable it to resist the strain of two thick strings, from one-tenth to one-fifth longer than those formerly employed to utter sounds of given pitch; but even if desired, a third string to each note, from fiddle G up to the highest note in the compass of the instrument. I should much like to see the opinion of your very practical correspondent, W. T.," on what he may term my unpractical proposed method of doing what is needed, which opinion he might include in the next of his promised papers on the economical improvement of old pianos-a contribution, now at least due, if not overdue, and which, judging from the communications which have been addressed to me privately, from several and sundry of my fellow readers of the ENGLISH MECHANIC, would be of considerable interest to those of my fellow readers who possess old pianos, and de-ire them to be economically improved. THE HARMONIOUS BLACKSMITH.

OXYHYDROGEN GAS STOVE.

SIR.-I fear that to give a reply to "Houblon," page 643, No. 2074, Vol. X., will occupy too much of your valuable space, although his question brings up a suggestion truly valuable to a great many of my brother readers, in obviating the pernicious stench and securing a greater intensity of heat given by the ordinary means of heating, &c., with coal gas. Fig. 1 represents a suggestion for boiling water for washing, for boiling and stewing in saucepans, and where frying may be done, and a shows the oven, in which roasting or baking may be done. Fig. 2 shows the top part of this gas stove. Two cast iron covers, a a anel eeee, of reasonable thickness, fit down a little within the outer edge of the top part of this stove, resting on bracket

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ing, as seen by the dotted line n n nn, which bracketing forms the seat for the washing boiler B, as seen in Fig. 3. Three holes of sufficient diameter are cast in these plates, two in the plate e and one in the plate a, with lids hhh, Figs. 2 and 3, hinged into the top bed of the stove. The two doors hi are laid back on the bearances b, when the cover plate e e e e is lifted off by the ring v to set in the large boiler for washing. Cooking may be going on in the oven m and on the back burner g. Fig. 2, a saucepan, may be set at the same time the washing is going on. The centre of these holes in the portable top plates, for stewing. frying, &c., must be direct over the gas burners. are the two front gas cocks, and ss the two front air cocks into the burner g. The air-vents w w are small holes about in. diameter, one to each burner, the holes y, which may be each 14in. diameter, holes fitted

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the top of the burner, fitted in the upright of the stove. a a represents a number of small holes in the outer edge of the top part of the part e all around. The top part or cover c may be taken off, and eggs or anything may be boiled in a pan placed on instead. For the supply of air continually, and sufficiently compressed, I recommend my centre fluid hydraulic, drawings and explanations of which shall, by your kind permission, appear in the ENGLISH MECHANIC shortly.

JOHN C. SHEWAN.

HARMONIUM REEDS-VARIETIES OF THE TIMBRE OF.

SIR, "P. E. H." asks if additional vibrators act only like additional strings on a piano, i.e., only increase its loudness, or if they can be made to imitate the sounds of the trumpet, oboe, elariouet, flute, &c. The only possible reply is that of the puppet showman, who exhibited the battle of Waterloo, in which the artist did not very clearly indicate the leading characters of that remarkably Christian-like and benevolent military encounter of the fellow worshippers of Him who taught brotherly love and peace to mankind, when the good little girl asked him, "Please sir, which is Napoleon, and which is the Duke of Wellington ?" Whichever you please, my pretty little dear. You pays your money and can have your own choice." If "P. E. His prepared to pay his money-and a good deal of it-h my purchase, within certain limits, the right to choose, not onl much tone as he desires, but the different kis f toue he prefers.

It is suffisently obvious that if two harmonium vibrat be m as nch alike as possible, and employ to pr dum ical sounds under as nearly as possible the auditions, the sounds they cause the utterance of will not differ much in character; in a word, they will act just like the second, third, fifth, sixth or seventh unisonous string of a pianoforte, and only augment the loudness of the instrument; but just as one string, tuned to the same pitch, may differ from another in thickness and length (and consequently its sounds differ in timbre), so the sound of one reed, which is thicker or wider in proportion to its length, may differ from another reed in its sound, not to mention that the character of the sounds, which are caused by the same reed, may differ greatly according to the treatment to which it is subjected, for in this respect harmonium reeds resemble human beings, and utter very different sounds, according as they are well or ill treated.

The most obvious means of varying what I may term the original sounds of harmonium reeds is to vary the proportions their lengths bear to their widths. It is hardly to be expected that the sound of a reed which is only twice as long as it is wide will very closely resemble that uttered by another whose length is from eight to twelve times its width, any more than we can obtain sounds of the same timbre from the long narrow pipes of the dulciana rank identical with those uttered by open diapason pipes of more than double their diameter. The character of the sounds we obtain from each will be in proportion to their sectional areas, like producing like, and we might as reasonably expect to gather grapes from thorns, or figs from thistles, as to obtain the full broad tone of the wide scale open diapason pipe from the narrow dulciana, or the beautiful quality of the latter from the former. No doubt the skilful voicer can do much by making mouths, but neither manipulation nor chemistry can yet wash the blackamoor quite white,

without also washing out his individual life; both he
and the pipe whose mouth is opened too much are only
fit to go "down among the dead men,"-you can't well
make them shut up.
Besides that variation of quality of sounds, induced
by varying the proportions of length to breadth,
different methods of affixing the reeds to their frames,
and different methods of forming the ree s, consider-
ably influence their timbre. Good workmanship can
do much, but, according to the late Mr. Myers, nothing
can compensate for the injurious consequences of the
reed and its frame being formed out of two pieces.
He used to say, which is true, that absolute contact
between them was beyond human art to effect, and
that an uncertain amount of chattering invariably
ensued when the reed was simply held to its frame by
a saddle or cross bar, screwed down on it Also, that
the best rivetting did not prevent chattering if the
reed was made of thin material instead of being forged
out of metal from 1-10th to 1-15th inch thick, and
very slightly shouldered on the side nearest its frame.
I have found this a very effective method of prevent-
ing chattering, but Mr. Myers had a great faith in his
patent method of construction, in which the reed is
cat out of the same substance of its own frame, and
only remains attached to it at the fixed end. That
his colophons, with hardened and spring tempered
steel reeds thus formed, produced tones of far greater
purity than any of their contemporary seraphines, I
can avouch, but that this was entirely due to their
reeds being made of the same piece of steel which
also formed their frames, I can't help doubting. I
suspect good workmanship had something to do with
it; but whatever the cause or causes might have
been, the effect was excellent. The eolophon differed
from the thin reedy seraphine nearly as much as a
fine organ reed, employed in unison with the open
diapason, differs from ye ancyente oboe, or vox
humana stop, voiced à la Punch, whose dulcet sounds
ye ancyent voicer of pipes evidently considered the
ne plus ultra of reed tone.

Not long since I heard an harmonium, by Ramsden, whose strident tones might have satisfied our MECHANIC's princess" Alexandra" herself. This instrument, which drowned every other in the room, had but one and a half row of reeds, whose tones remarkably resembled some of those German concertinas which so greatly surpass their English namesakes in power and-if I may be allowed to coin an adjective-also in horniness. Possibly great pressure of wind had something to do with the matter, for I find the steel reeds of my Day and Munck's colophon assume this quality when forced. I suspect the physharmonica with a swell (not, of course, the organist himself, although some of them are both great swells and heavy swells to boot), with its free reeds blown by 10 or 12in. wind, has something of this strident character, and sounds very unlike the tender reeds of an Evans's or Hermann Smith's chamber harmonium, which are delicately blown, and perhaps also-as all good tender children should be-well wrapped up to keep them from squalling.

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two or more ranks of keys, that perhaps
(who is no eleve at all in the matter of harmoniums,
excepting in the sense that the wisest of us have
something to learn) or Mr. H. Smith would kindly
express his opinions on this method of varying both
the power and quality of the sounds of this instru
ment, for, if desirable, it is extremely cheap, only
requiring one or two extra weights to be put on the
bellows at the performer's pleasure, and this may be
readily done by disconnecting their supports; or if
the use of weight be prohibited, by allowing additional
springs to come into action.

rately the exact ratio of disturbance originating from this source, as it varies so much under different circumstances, nor can we hope to eliminate it entirely until the good old form of the Cassegrainian or Gregorian telescopes come again into general use. An open tube could then be used with great advantage, which seems rather to increase the disturbance from this cause in the Newtonian telescope.

There is, however, no comparison whatever in the relative greatness of this source of indistinctness, between the Newtonian and front view construction. Of all the forms ever devised, the last-mentioned telescope is so completely at the mercy of these troublesome cyclones that, leaving out of considera tion the spherical aberration, sharpness of definition is almost, if not quite, impossible, in such a telescope certainly, if the correspondent, who sent you a sketch of his telescope lately is the happy possessor of one of those large heads, so highly spoken of in a recent number, very little light, and that of a very tumultuous character, can ever reach his 12 n. mirror.

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That any free reed instrument will ever render that
wide variety of timbre obtainable from organ pipes
is hardly to be hoped for. If anything at all like it
could be done, the instrument would well deserve the
name of wind organ, but I am far from believing that
our so-called wind in trument stops, whose names are
engraved on its draw, exhaustively represent the
capabilities of reeds for producing sounds of different
timbres. I suspect it is rather because no one has yet
shown what can be done, and how to do it, such an While speaking of this form of telescope,
instrument has not been made, and that no commer- sorry to read the abrupt manner in which your
cial demand exists for harmoniums with greater talented correspondent "F.R. A.S." took up a remark
variety of tone. "Alexandra "only asks for what every of "Arcturus' with regard to spherical mirrors.
organist who performs on a tolerably large instru- Your worthy correspondent has always been so cour-
meat with a swell, already possesses; and if she can teous in his replies, and so ready to assist us at all
induce some expert, cheaply to supply her require- times, that we should expect, for one who has taken
ments with free reeds, which at present are only to be so much trouble to enlighten our minds on the mecha-
supplied by pipes at great original expense, not to nical minutiae of speculum grinding and polishing,
mention the cost and trouble of the oft-repeated and to teach us lessons which are rarely, if ever,
tunings which a large pipe organ with many reeds learned from professional astronomers or opticians,
requires, she will have the satisfaction of having better treatment at his hands. I can hardly see how
caused an addition to the number of the good things" F.R.A.S." would, in any degree, trench upon the
of this world to be brought into existence, and for one just estimate he has formed of the absolute necessity
I heartily thank her for asking for it; indeed I con- for the parabolic curve, if true definition is to be
sider her request an example of that refined musical attained, were he to confess with Sir John Herschel,
taste which invariably distinguishes her sex.
"that for this construction it is needless to insist on
THE HARMONIOUS BLACKSMITH, the parabolic curve." My own experience is, that the
spherical aberration of a mirror, parabolised in the
usual way, is quite equal to, if not greater, than that
of a good spherical one, when tilted at an angle of $
and 4 degrees, and that experience was learned from
most perfect 4in. speculum by With. For preserving
the silver films of these glass mirrors, if the observer
does not wish to remove them from the telescope each
time he has finished using it, I have found no plan so
efficacious as to turn the tube itself into an air-tight
cell; this is easily done by having it made perfectly
stanch in all its seams, and having a lid for the mouth
which fits most closely and neatly; to this lid is
attached, by a string, a long roll of some light fabric
which has been steeped in chloride of calcium, and
thoroughly dried in an oven or at the fire, before in-
serting it into the telescope. It will quickly absorb
all the moisture in the tube, and as no more can creep
in so long as it is closed, will keep the silver surface
perfectly dry and bright. I have often thought, how-
ever, that some of your clever chemical correspon-
dents would be conferring an incalculable benefit on
the possessors of these telescopes if they could dis-
cover some method for precipitating pure aluminium
on glass; it is of an exquisite white colour, of very
close grain, and receives a higher polish than even
silver itself, and might tend to render them quite
equal to refractors in light-grasping power, as they
are at present in defining power.

REFLECTORS AND REFRACTORS.
(Continued from page 11.)
SIR,-The telescope was next directed to the two
nebula before-mentioned. We shall now only give our
impressions of the latter (M. 13 Herculis); and what a
wonderful sight we beheld when it was brought into
the field of view! With a low power a small, bright
cloud, all sparkling with diamond points of light, but
with a higher power how magnificent the change!
Stars piled upon stars, not one trace of the cloud
remaining, but star-dust, even to the very centre,
where they seem so infinitely close, that one wonders
they each can still be seen separate from the other.
Here is a test for the perfection of figure of a specu-
lum, than which none could be more severe. To com-
pletely resolve this superb cluster, even to the very
centre, with such an aperture, is work any man might
feel proud of. On the second evening I examined this
object most carefully, and for some time, and could
most distinctly trace the two dark rifts first seen in
the Earl of Rosse's great telescope. They were best
viewed with the highest power I used (350).
But enough has been said to show the extreme
excellence of the speculum I was employing, and the
sufficient adaptability of the mounting described in a
former letter." Let every amateur take courage, and
if he only possess a little ingenuity and patience, he
may do even better than I have done. The above is
but a short account of one or two nights' work-very
favourable nights, I will admit, and such as do not
come very often, but when they do amply repay the
earnest student any small additional outlay he may
have made in procuring a really good speculum or
object glass. Whatever he does, let the beginner
beware of cheap object glasses or specula; they always
break down when such testing times
prove ultimately a loss rather than a gain.
I would rather possess a really good 24in., or even
2in. object glass, than a cheap 3in.; and this reason-
ing holds good, a fortiori, with regard to specula of
respectively larger aperture, as with them the evil is
increased in a threefold degree.

"

come, and

This wrapping up is a very effective method of subduing unpleasant sounds. Every paterfamilias knows -to his horror-that his infant's eries are strident, indeed, if heard in their native nakedness, but become quite bearable when its dear little head is under the bedclothes. It won't do to let the infant breathe too freely, or he becomes "the son of the sleepless"; and even if this mode of quieting sometimes be fatal to it, we have at least the consolation of knowing that its departure to the world of spirits diminishes that pressure of population on the means of subsistence which political economists so earnestly deprecate. No doubt the reader will say there is nothing new in this, it having long been familiar to "ye family man,' but if not new itself, we have not long since become acquainted with a new application of this very old fact, which new application well deserves letters patent not only to be granted gratuitously, but also that its inventors should be fully paid for their ingenuity. I need hardly say that I allude to the late Shoreditch infirmary practice, in which a noisy pauper -what right can paupers have to make a noise ?-was duly and effectually quieted by having a cloth forcibly There is one fact, however, which I have learned held over his wicked mouth, while the nuss prepared from constant observation; it is that when the air is a sufficient dose of morphia to quiet him effectually unsteady there is no use in trying to use an aperture until the day of resurrection, on Count Fosco's prin- of 84in. perhaps this may seem too strong an assertion ciple of assisting tired Nature's tendency to perma- to some, but certainly the position in which my telenent repose. Verily we do improve in the treatment scope is placed-a position very similar to that deof insane paupers, for not only do we liberally pro-scribed by Mr. Purkiss (near a large city-has taught vide wet cloths for their crying necessities, but also me its truth. Many nights come when I can use expensive medicines, dispensed with a liberal hand by smaller apertures, and see planetary and lunar details nusses, to assist their progress out of all mundane sufficiently well to learn something of phenomena taking place in those bodies, which a larger aperture would not even suggest.

miseries.

To return to our dead sheep (muttons, as the French say). I very strongly suspect the reeds whose draw stops are duly labelled clarionet, hautbois, and most of the other varieties of timbre we hear from the harmonium (or rather ought to hear). Too often the real tones are very far indeed from that instrument, are much more due to the different areas of the spaces between the reeds and the pallets (within which spaces the air, under the influence of the reeds, becomes resonant), and the quantity of what I take the liberty of terming bedclothes (interposed between the reeds and the hearer), than to any other causes-of course I mean the extent to which the reeds are covered up. I am told the popular voix celeste-which can only be termed celestial on the hypothesis that the angels practice singing the music of the spheres (whatever that music may be), with remarkably thin reedy voices-is produced by another dodge, but instead of enlarging and perhaps yet further exposing my own ignorance on this not very celestial subject. I would recommend the reader to peruse Mr. Hermann Smith's paper on it, for an expert can, if he will, almost invariably give us more information than any mere amateur, however clever he may make the very common mistake of thinking himself.

But few modern harmoniums which I have seen are constructed with the means of blowing their reeds with wind of different pressures, without using the expression stop. Myers and Storer, 1839, and Hewett, 1838, patented methods of doing this, with only one bellows, and, I believe, others have since invented other ways of effecting it. The thing seems to me so very desirable, especially for instruments with

Nights often come when it is vain to attempt to divide even such a star as a Herculis with the whole aperture, or see the transits of Jupiter's satellites, yet a lesser aperture of 5 or 6in. will accomplish both tolerably well; unfortunately too, these are the kind of nights which predominate in our climate. This I say with great deference to Mr. C. Key's opinion, which is deserving of the highest respect, but it has forced itself again and again on my notice, and were I asked to advise one of your correspondents who was anxious to possess a telescope which he could use on most bright nights, and was not willing to keep a large one in reserve to use on good occasions only, I should strongly recommend a refractor of from 3 to 4in. There is a calmness of definition in a refractor, arising from the air between the object glass and eye-piece being shut in, and nearly free from disturbance, which has greatly tended to induce a preference for that instrument over the reflector. This freedom from air currents is frequently mistaken for a greater sharpness of definition, whereas it may be stated with all confidence that a reflector, if it be a really good one, is, on favourable occasions, equal to the very best refractor of the same aperture, only those favourable occasions do not come quite so often with the former as with the latter.

The position of the eye-piece in the Newtonian telescope, as it is generally placed, has something to do with these tube currents, for the heat from the observer is almost necessarily brought in contact with the air in front of the tube, and with the surface of the tube itself; it would be very difficult to estimate accu

I see in a letter from one of your excellent practical correspondents, that he paid £2 for a focussing metion" to the eye-piece of his telescope; now for about one-sixth of that sum he could have procured a plate lens, secondhand, with rack motion. Having taken out the lenses, he could easily have fitted the spring-tube of his eye-piece to this, and thus have obtained a most excellent and simple focussing motion. This plan is not mine, as I feel sure many of your correspondents have seen telescopes so

mounted.

The most pleasant "finder" possible, can be formed by placing a rectangular prism before the eye-piece of the finder, and so turning the rays out parallel to those from the large mirror after they pass the "plane. By this plan you have only to turn your eye from one eye-piece to the other, while still rechning in your chair, and need not strain either your neck or your eyes to find what you may wish to observe. I cannot close this letter without two words of thanks, first to yourself for the successful manner in which you have conducted your most excellent journal of late, and the abundant store of really useful information you have managed to obtain for its pages from those whose "fame is in all lands," an secondly, to your generous and patient correspondent, Mr. Purkiss, who has made a real discovery in the science of speculum testing, and one of the very greatest value to all those interested in the subject. 1 bave tested it myself, and believed it possible, with due attention to particulars, to attain, by the means he suggests, a mirror of any size, perfectly free from spherical aberration.

P.S.-I am vesy glad to see Mr. Wray's name brought before your readers in a recent number by the Rev. Mr. Webb. I have two object-glasses by him, one a 2 8-10ths inch, already mentioned, the most perfect of its kind I have ever seen, the other 4in., recently obtained, which quite surprised me by its light grasping power. On two occasions I have distinctly seen the 6th star in the "Trapezium" of Orion, a test I used to consider far beyond such an aperture. I do not mention these matters by way of advertisement, but to assist those in search of really good object glasses, and to whom the price is a very important consideration. If the amateur can save £5 in the purchase of an object-glass, and obtain a really good one, he has the money in hand to purchase s battery of eye-pieces, no mean consideration after all.

HYPERION.

EXTRACTS FROM CORRESPONDENCE.

NOMMES DE PLUME-" Neptune," in a letter full of congratulations, says: One of the interesting features of the ENGLISH MECHANIC is the great variety of assumed names under which correspondents write. Where they all come from I cannot imagine,

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