The figure (erroneously marked by our draughtsman Fig. 2), represents a transverse section of the spiral, with the manner in which it receives the water showing at the same ting

feet diameter, and 24 feet long, the spiral will require 24 feet stream to make one revolution; which is not the case with the water-wheel, as will be immediately shown. Again, the spiral has no tail water, as all other mills have; the water passes along the spiral as a nut passes the screw.

wheel. The adjoining figure repre sents an under-shot wheel in floody water, or when the river is high, and the water up to its shaft. In this state, the under-shot wheel will scarcely move round, and is liable to be stripped of its floats, as may have been fre quently seen at London-bridge waterworks. The upper figure in the pre

streams, with or without a water; and may also be erected in addition to other wheels, so that the water may do double its present labour; neither can it be obstructed by floods, as all other wheels are.

The

lower figure on this page represents a scale of the solid feet which the spiral contains, according to the dif ferent depths of water which it may have acting on it. The right hand of the two undermost figures in the preceding page, represents a breastwheel, of 16 feet diameter, which employs as much water as the spiral does, while it is one-third less in diameter, which makes it one-third less in power. Again, the spiral runs one-third quicker, which makes the spiral so much superior to the breast

wheel in its greatest power. The water is acting on four of its floats only; and 48 feet run of water are required to make one revolution, while the spiral would take but 24 fcet. JOHN NORTON.

[Our draughtsman, by not choosing to mark the figures as he found them in the original, has obliged us to be very circumlocutory in our de scription; but we trust it is sufficiently intelligille. EDIT.]

ENGLISH MUSICAL WIRE. No. 3, Nassau street, Sobo Feb. 17, 1824. GENTLEMEN-In No. 25 of your very useful Magazine I observe a communication from a person signing himself "Truth," purporting to

an answer and refutation of the matter advanced in a letter addressed to you by Mr. Gunby, on the subject of English manufactured wire for musical purposes.

I believe that Mr. Gunby's communication was entirely unknown to, and without the authority of Mr. Deakin or Mr. Lewis; for the publication of a statement so deficient and incorrect would not have been permitted by either of those gentlemen.

The person signing himself" Truth," says, "that he is no stranger to Mr. Deakin's wire; that it has been tried, and found much inferior to good Berlin wire;" he admits, or "has not much doubt that it will bear as great a strain in a straight line," but denies the possibility of stringing instruments in the ordinary way with it," as it snaps at once.' Now, I will venture to affirm, that not one word of this is true; the wire made by Mr. Deakin for musical purposes is a tempered steel wire, which, at a given temper, is sufficiently flexible to coil round a pin in the ordinary way, in which state its cohesion is greater by 20 to 30 per cent than any Berlin wire of equal size which I have ever used, or seen used. I have now standing upon an instrument several strings of Mr. Deakin's wire, put on in the ordinary way (to replace others of the Berlin wire, which broke in tuning), and which will bear the tension of a whole tone above concert pitch. The scale of this instrument is an equal ratio, and the length of C on the first ledger-line below is 24 inches, which is one inch longer than is usually given. With regard to the complicated fastening which your correspondent has mentioned, it is in principle and application very simple, and affords a facility and precision in tuning, of which the common wrest-pin is incapable. With this fastening Mr. Deakin's wire will, when at that temper which affords the greatest possible power of cohegion, stand at concert pitch, when middle C is 16 inches long (being 4 inches longer than the best Berlin wire will stand at); at this tension I have some now standing upon a new instrument, and there is still enough of cohesive reserve to raise the pitch another tone."

Your correspondent has made an allusion to what he terms a discovery of Lord Stanhope's, similar to that of Mr. Deakin's. But here again his assertion is incorrect; the wire used under the direction of Lord Stanhope was a common steel wire, not tempered, and very thick; I believe the smallest size was nearly one-sixteenth of an inch in diameter, and graduated to nearly three-sixteenths in the bass; these wires were soldered to the fastenings.

I shall feel much obliged to your correspondent if he will favour me with a piece of the wire, which he says he "prepared in a particular manner," in return for which I shall be very happy to convince him of his erroneous opinion by ocular proof of what I have here stated, but cannot hold any further communication with anonymous signatures. I remain, Gentlemen,

Your obedient servant,
E. DAVIES,
Piano-Forte Maker.

THE RAISED ROOF. GENTLEMEN;-I should not have again troubled you on the subject of

the Raised Roof," had Mr. Horsfall been more explicit in the mode used in raising it. The roof is of common construction, and it still appears to me, that unless the rafters were first disengaged from the purlins, ridge, &c. they could not have been raised in succession. My doubts were not as to the powers of the hydraulic press; only as to the mode of aps plying those powers, and I should feel obliged if Mr. H. would favour me with a more ample account of the process; for as it sometimes occurs to me in the course of business to place an additional story to a house, I should like to be able to perform it with greater facility.

AN OLD CARPENTER.

P. S.-In order to assist Mr. H. in his description, I have subjoined the names of each number:

(For the Mechanic's Magazine.)

Red Lion Street, Clerkenwell. SIR-I have seen many of my brother tradesmen very much puzzled about drawing the segment of a circle with a long radius. I therefore think it right to send you a method which I have often prac.. tised; its principles are mathematically correct. Suppose I have a segment to describe, whose chord D C is 50 feet, and versed sine EF 12 inches. Then, in order to effect this, I take a board, A B C D, 50 feet long, and 12 inches broad; and another board, DEBC, in the form of a trapezoid, the length, E B, being 25 feet, or the half of the chord and breadth, or versed sine of the intended segment, E F, equal to 12 inches.

place two nails, D and E, into the board A B C D, and by sliding the sides, D E, E B, of the trapezoid in the direction B E, the point E will trace the half of the intended segment, as represented by the dotted line; the other half may be traced out by a similar process. Now, the truth of this construction is manifest from Euclid, Book 3, Proposition 21; for, the line D E, and angle DE B, are fixed and invariables

J. Y.

IMPROVEMENT IN WATCHES
SUGGESTED..

Experience has proved, that however well watches may be made to perform by the ordinary work, yet they cannot be considered eligible to be depended on for true time without

compensation balance (which is very expensive) in consequence of the expansion and contraction of either the brass or steel balances; besides

that, the steel balances being or becoming more or less magnetic, it has occurred to me, that balanoes made of either cornelian or Brazil pebble (such as are in some specta cles) would not only be extremely cheap, but look beautiful, and entirely remedy the evils I have named: They might be made either solid, with the spring on the top, like chrono meters; or, by having three large holes bored in each, nearly the shape of three bars would he left; as these would, of course, be lighter than steel, they might be either made thicker to obtain more weight, or the diameter might be increased in due proportion. I shall be glad of a scientific opinion on this subject. W. G. P.

THE IMPROVED BOAT FOR WEIGHING ANCHORS.

6

Woolwich, Feb. 4, 1824, GENTLEMEN;I perceive in your Number of Saturday, 31st Jan, an article headed. "The Important Nautical Improvement," wherein your correspondent G. B. of Rotherhithe states, that on mentioning what appeared in your Number of the 17th on that subject to an old shipwright," he assured him, "that he had seen such many years ago, and that at one time all the Indiamen, and many ships of war, had their boats fitted in that way," and then thinks it but right " to apprise you of it, in order to correct any misunders standing on the part of your readers as to its being a new invention."

-There can be no doubt but your correspondent's motives are perfectly correct and praiseworthy, and, as such, he is entitled to the thanks of all your readers; but perhaps it would have been equally desirable had he informed himself of the true state of the