ECONOMY IN FIRE WOOD-MR. SPEER'S CONCENTRIC CHUCK.

26 MECHANICS' INSTITUTION AT CRAYFORD-MR. COBBETT'S STOVE.

many scientific and practical men, both engine, tool, and lathe makers, and persons professionally acquainted with turning in all its branches. Both our Chairmen of Mechanics were present, one of whom, you cannot but know, is an engineer of the first eminence, and who, I suppose, your sapient and veracious Correspondent will allow is not " very ignorant of the tools used in an engineer's workshop." The claim to novelty was particularly discussed, and the evidence of several practical men taken as to that point, as appears by the minutes of the Committee.

I have also, both before and since I submitted this chuck to the consideration of the Society of Arts, shown it to several lathe-makers and turners, all of whom have declared that they never saw any on a similar principle before.

I am, Sir,
Your obedient servant,
E. SPEER.

7, New Inn, April 5th, 1825.

ral meeting assembled, and consists of operatives only. A reference and circulating library is forming; and, as soon as our funds will admit, apparatus will be purchased, to enable the members to become their own lecturers. The members meet every Wednesday evening. Visitors pay sixpence each, and sons and apprentices of members will be permitted to attend gratuitously.

Such is the brief outline of our infant Institution; the establishment of which we owe to the exertions of the Rev. Thomas White, Dr. Gregory, John Fassett Burnett, Esq., and other principal inhabitants of Crayford.

By giving this communication an early place in the Mechanics' Magazine, you may induce other manufacturing villages to follow our example, and will confer an especial favour on your constant reader, and a warm friend to the general diffusion of scientific knowledge, WILLIAM WALKER. Crayford, March 29th, 1825.

To the Editor of the Mechanics' Magazine.

SIR, As the friend of operative mechanics and artisans, you will be gratified by the information, that a Mechanics' Institution has been established in the little manufacturing village of Crayford, in Kent; and that Dr. Olinthus Gregory has very politely offered his services to the Institution.

The Doctor gave his first Lecture on Mechanics in the National School Room, on Friday evening last, to a very respectable audience of ladies, gentlemen, and operative mechanics, who evinced the interest they took in the lecture and the good of the Institution, by the profoundest silence and attention during the lecture, and by an unanimous vote of thanks to Dr. Gregory at its conclusion.

The members of the Crayford Mechanics' Institution pay twopence a-week each. The Institution is governed by a Committee, chosen by the operative mechanics in gene

MR. COBBETT'S STOVE. SIR,-W. T. appears to be rather angry that Mr. Cobbett's Fire-place should be disapproved by any one, and pettishly states his belief, that "if he (Mr. C.) was to do the most unobjectionable and meritorious thing imaginable, there would be found some to doubt his good motives, and others to misrepresent them."

Now, Sir, without at all disputing Mr. Cobbett's good motives, I must observe, that W.T. can know but little of the world, if he is not fully sensible that public characters place themselves in that situation, that their writings and assertions are descanted upon and discussed more than other men, and this is naturally and fairly the case; for what should prevent me, or you, or any one else, who differ in opinion from this great Leviathan in the political world, from stating such dissent from hi:n, together with the reasons for it? Mr. C. is, or has been, a great champion for freedom of discussion and the liberty of the

EFFECT OF IRON MASTS AND CHIMNEYS ON THE COMPASS.

press; but his advocate, W. T., one may almost be led to suspect, is hostile to these liberal sentiments.

In respect to the illiberality with which I am indirectly charged by W. T., I must observe, that having read Mr. C.'s overdrawn statements of the many excellent qualities of this stove, I was induced to inspect it, and must own that I was greatly disappointed, on being shown so filthy, clumsy an article, as the highly-praised American stove in question. Now, as respects myself, or such persons who have an opportunity to see and judge for themselves, the consequence is but trifling; but to such of your readers who live at a distance in the country, and who have no other means of forming an opinion, except what may be gathered from the Political Register, the case is very different, and it was principally to guard these from disappointment, by trusting to such statements, that the article in your 80th Number was intended; and I have to remark, that W. T.'s assertion that Mr. Cobbett has given his readers and the public an engraved representation of the stove represented by him, is not correct. It is true, that an engraving has been given in one of Mr. C.'s subsequent numbers, but it appears that this engraving was furnished by the person who makes the stove, and is very unlike that recommended by Mr. C.; in fact, he disowns it. It is so altered (like Peter's coat in the Tale of a Tub), that it is quite different from the original. "The enclosed body," says Mr. C. (I have not his Register at hand to refer to his exact words, but I "know that I am right in substance), "is not mine; neither the ornament nor the burning martyrs," as he terms the figures "I want none of them; two bricks being all that I use to keep the fire together." An elegant mode truly, and which must look admirably in a gentleman's drawing-room. Still the body, as introduced in the engraving, is an improvement, and is what I recommended in my former statement, inserted in your 80th Number; but, upon the whole, my opinion of its merits remains unaltered; for unless the projecting sides and hearth-plate

27

can be done away with, it will never
be fit for the parlour; and, as re-
spects a cooking apparatus, I again
repeat it is totally out of the ques-
tion, there being scarcely room or
convenience even for a Welchman to
toast his cheese.

I am, Sir,
Your humble servant,

April 2, 1825.

T. J.

EFFECT OF IRON MASTS AND IRON
STEAM-CHIMNEYS ON THE COM-

PASS.

"

Professor Barlow having been requested to give his opinion as to the probable efect which the projected hollow iron masts (see M. M. p. 432, vol. 111.) in men of war might have on the he returned for ancompass, swer, that he thought it probable so great a surface carried above the deck would have a counteracting effect on the usual iron of the vessel, by bringing the common centre of attraction of all the iron nearly into a horizontal plane with the compass, and therefore, in these latitudes, nearly into the plane of no attraction, so as to leave it doubtful whether the actual effect would be the same as, or the reverse of, what happens in the usual cases. If the power of the mast prevailed over the other iron, the effect would be reversed; but if, on the other hand, it did not amount to so much, then the effect would remain the same in quality, but would be diminished in quantity."

Mr. Barlow has since made a series of experiments to determine the local attraction of steam-vessels, which present nearly a similar arrangement of materials to a vessel with an iron mast; the iron chimney standing in place of the mast, and the boiler and engine in lieu of the usual iron tanks, ballast, and guns. The result of these experiments fully confirms the theoretical opinion advanced by the learned Professor. The counteracting power of the chimney was rendered very obvious, the local attraction having been found very inconsiderable, and just such as might have

28

86

FRAUNHOFER'S REFRACTING TELESCOPE.

been predicted from the circumstance of elevating the common centre of attraction, as in the case of the iron mast above-mentioned.

It appeared from another set of observations which the Professor made with two compasses, one in the fore and the other in the aft line of the vessel (Comet steam-packet), that, with the ship's head to the east, the north end was repelled to the west, and with the head to the west, the north end passed to the east of its true bearing, which shows that the result was either due to the superior action of the chimney, or to some iron abaft the wheel, being directly the reverse of what generally takes place in the usual order of vessels in these latitudes. "Whether this," says the Professor, "is the case in all steam-vessels with iron chimneys, may be worth the inquiry of those engaged in the navigation of them, particularly in those intended for voyages."

FRAUNHOFER'S REFRACTING

TELESCOPE.

A Refracting Telescope, of extraordinary power, manufactured by the celebrated Fraunhofer, has just been erected at the Observatory of Dorpat. When in a perpendicular position, the height of the object-glass is 16 feet 4 inches (Paris measure) from the floor, 13 feet 7 inches of which belong to the telescope itself, so that the eye-glass stands 2 feet 7 inches from the floor. The diameter of the object-glass is 9 Paris inches (about 9 inches English). The weight of the whole instrument is about 3000 Russian pounds. It is so constructed that it may be used as an equatorial. The upper part of the instrument consists of the tube, with its axis of motion, two graduated circles, and a variety of levers and counterpoises, producing the most perfect equilibrium in every direction, and providing against all friction. The declination circle is directed from 10 to 10', but, by means of the vermice, may be read off to 5". The instrument may be turned in declination with the finger, and round the polar

axes with still less force. The most perfect motion round the polar axes is produced by means of clock-work, which is the principal feature of this instrument, and the greatest triumph for the artist, the mechanism being as simple as it is ingenious. A weight, attached to a projection connected with an endless screw, overcomes the friction of the machine. The clock, vibrating in a circle, regulates the motion by moving an endless screw, connected with a second wheel in the above projection. The weight of the clock, as well as that of the friction, may be wound up without the motion being interrupted. When the telescope is thus kept in motion, the star will remain quietly in the centre, even when magnified 700 times; at the same time, there is not the least shake or wavering of the tube, and it seems as if we were observing an immovable sky. But the artist has done still more; he has introduced a hand on a graduated dial of the clock, by which the motion of the latter can be instantly altered; so that a star may be brought to any point of the field of vision to which it may suit the observer to carry it, according as it is required to make the course of the instrument go faster or slower than the motion of the heavens; and if once placed, it may be kept in that position by returning the hand to its original position. The same mechanism is also used to make the motion of the instrument coincide with that of the sun and

moon.

This instrument has four eyeglasses, the least of which magnifies 175 times, and the largest 700 times. Professor Struve has compared the power of this telescope with Shroëter's 25 feet reflector, by means of which that astronomer saw the constellation of Orion twelve or thirteen fold; whereas Struve clearly ascertained the existence of sixteen distinct stars. This instrument is furnished with four annular micrometers of Fraunhofer's construction, and an excellent net micrometer of the same artist. means of these, it appears that the probable error in the measurement of some minute distances, of 7′′ and

By

WATER-CLOCK-UNSINEWING TURKEYS-ATMOSPHERIC PRESSURE. 29

under, did not exceed the 18th part of a second. The expense of this instrument was about 9501. sterling.