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EXPERIMENTS IN EROSTATION.

also slacken the screw 2, so that the axis F may turn; while turning the pinion V replace the bars I and K, and set L at any angle, say 45°; then upon turning the pinion G, the nut will advance along the groove in D, and pressing against the oblique bar L, will cause K to pass over an equal space along the groove in I, and if the tracer on Q is set so as to coincide with any part of the diameter I, it will describe a spiral of equal distances; but if the tracer be set so as not to coincide with I-as for instance, if it be set any where along the line K-the distance between each turn of the spiral will vary. The number of spirals will be as the number of threads on the axis F, in the space between the nut H and the bar I, divided by the number of revolutions the pinion G makes in passing once over the periphery of the ring B; but should a greater number of spirals be required, then to shift the nut H back again to E, and the bar K to its original situation, slide the tracer on Q to the point where the spiral terminated, and a second and third set of spirals may be drawn, all observing the same law of curvature. The distance between the spirals will be less as the angle of L with K is less.

The invention (such as it is) is entirely my own, with the exception of the method of describing ellipses, for which I am partly indebted to Mr. Child; and also, in some measure, to Mr. Jopling, who has shewn the principle in his "Three Cases of Harmony," in the Mechanics' Magazine: but I should not be at all surprised to find that I am by no means the original inventor; therefore, should any of your readers be aware of a similar instrument being recorded in any work, I shall feel nowise mortified by their pointing it out to

Your most obedient servant,
J. MURDOCH,

Mech. Draftsman. 4, Vittoria-place, Mile-End-road, August 18, 1829.

EXPERIMENTS IN EROSTATION.

Sir,-Observing several of your pages occupied by theories on the art

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I was led to entertain the notion of the facility of a man flying as a bird, by noticing the rapid progress of the carrion gull, who with expanded wings can make way against the greatest storm, and may be seen at times to go half a mile without wafting a wing. Now, I would ask how does he gain his way against so strong a current of wind without wafting his wings? We easily comprehend how a bird may win his way against wind, by proportionably strong efforts of its wings: but here is a ponderous floating body without visible efforts, moving on against the strongest current of air at the rate of six miles an hour. On contemplating the subject, I formed the idea that the movement was effected by the de-, scent of the bird on a plane so acutely inclined to the horizon as to render the descent of the bird insensible to the eye of an observer. Struck with.

this apparent cause, I farther conceived the idea that the common kite of the boys might afford means to elucidate the fact. To this end, I caused a kite to be constructed capable of folding or doubling, by having. two shafts in the centre united by hinges, so that by a cross-stick at the back of the kite, I was enabled, by relaxing a string which passed through the centre shaft, to reduce the angle formed by the two wings of the kite to any degree I pleased. To this kite I attached two lines; one to the usual belly-band, as the boys call it; the other was made fast to the lower point of the centre shaft; both lines passed through a small brass ring, which ring was again fastened to a piece of twine one-third the length of the kite, and fastened to its centre. When the kite was elevated by holding the upper line, I perceived I could at any moment cause it to descend by pulling the lower line; thus by alter nately pulling one or the other, its elevation or depression was effected

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BATH MECHANICS' INSTITUTION.

by the alteration of the angle which the kite held to the plane of the horizon; and by altering the halyard of the back-stick or yard, whose extreme ends run through two rings fastened to the points of each wing, I could reduce the surface of the kite conformably to the power of the wind. Now, if a man had a kite of the above description elevated over his head by machinery, enabling him to waft the wings and alter the angle readily to any plane with the horizon, I do not see why he might not by practice fly as a bird; at all events, I think that a balloon would be governed by such an appendage.

Although kites have been a common source of amusement amongst youth for time immemorial, I do not know that any such alteration in the mode of constructing or flying them, as I have mentioned, has ever been introduced.

Thus, Sir, we see from what trivial and every-day subjects we might derive assistance in forwarding science; and doubtless a contemplation of the works of Nature furnishes the best hints for our instruction in the fabrication of machines. Should these observations on the flight of the gull, or the little experiment of the kite, be deemed by you worthy the attention of those who have written on the subjeet, you will confer a favour on an old subscriber, by giving them insertion in your excellent Magazine. J. W.

Tullamore, Sept. 8, 1829.

BATH MECHANICS' INSTITUTION. Sir,-Your known attachment to every thing calculated to improve the morals, and increase the small sum of happiness that falls to the lot of the working classes of this country, has induced me to lay before you an account of an unsuccessful attempt to subvert the principles of the Bath Mechanics' Institution. The insertion of this in your valuable Magazine, I think will act as a warning to those who may wish to make similar attempts on other Mechanics' Institutions; and as an example to shew what can be done by a determined and well-directed opposition.

In the year 1825, a communication in the Bath Journal drew together a great number of the working classes of this city, who at a public meeting, founded the Bath Mechanics' Institution. About fifty persons joined in the first instance; the number very shortly increased to one hundred, between which and two hundred, it has remained ever since; more than twothirds of the members, on an average, being of the working classes. The present number is about one hundred and twenty, by whose subscriptions, and the liberal aid granted by several enlightened individuals of the city, we have at all times kept out of debt, and collected upwards of a thousand volumes, all of a useful character, a stock of apparatus, natural curiosities, maps, &c. &c.

Into this Institution, like many others, a great deal of lukewarmness crept, and the members became inattentive to the election of their committees, &c., notwithstanding the advice given them in a letter which they received from Mr. Brougham on that subject. In consequence, a party sprung up among us, denominated " The Genteels" by the working classes, because of their dislike to the term mechanic, and of their assuming a superiority over men, as good, and more valuable to society than themselves.

The rooms we at present occupy being thought inconvenient, a negociation was commenced some time ago with our President, for rooms in a new building he intended to erect, and which is now nearly finished. Our President demanded 60 guineas per annum for them; but with our present resources, £25. a year for rent is as much as we can afford to pay. As no positive or binding agreement had been made with the Doctor, at a general meeting, some of the members, whose eyes were open to the danger, cried off, for fear of embarrassment. "The Genteels" thought otherwise, and having fixed their hearts on going to the new rooms, they proceeded to carry into execution the following preparatory measures at the last quarterly meeting in July:-The first was a change in name, from "Bath Mechanics' Institution" to "Bath Society of Arts and Sciences." The old name

BATH MECHANICS' INSTITUTION.

was thought by "The Genteels" not sufficiently expressive or grand for the new rooms, and it certainly was not for the Institution which it was their secret intention to have established there. And, second, a rise in the annual subscription from ten to fourteen shillings for adults, and from six to eight for minors, to meet the extra demand for rent. Both these measures were calculated to hasten the retirement of the working classes,—the object to be gained by "The Genteels" especially when it was known to be their intention to increase the annual payment, ere long, to £1. "Not too fast-let it be fourteen shillings first," were the words.

In consequence of a very thin meeting of the members, these destructive measures were carried easily, and "The Genteels" had the insolence to raise an indecent shout of triumph when the decision in favour of the change was announced. These doings, however, completely opened the eyes of the lukewarm; several communications appeared in the Bath Journal, pointing out the danger, and calling on the members to exert themselves to rescue the Institution from the gripe of "The Genteels." The efforts of the writers were crowned with success; an efficient opposition was formed, prepared to oppose every thing calculated to deprive the working classes of the benefit to be derived from an Institution founded for their especial use.

The President now called a special meeting, and three other new names for the Institution were proposed, as being more palateable to our saucy stomachs. But the ungrateful dogs were stubborn, and not only rejected all of them, but called another special meeting, August 26th, to reconsider the resolutions passed at the last quarterly meeting. A very numerous assembly of the members took place on this occasion, every one of the obnoxious resolutions was repealed, and "The Genteels" completely defeated; ONE of them only had the spirit to hold up his hand in support of measures, for the success of which, on a former occasion, an indecent shout of exultation had been raised.

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Our President put a stop to the negociations respecting his rooms, thereby relieving us from all apprehension on that subject. If we had removed to his rooms, nothing but disaster would have followed such a step. The first year's expences could not have been less than £120; our revenue to meet it only about £60. In fact, a complete annihilation of the Institution, as a Mechanics' Institution, must have followed; and the valuable library, and other property of the members, would have slipped into the hands of persons, for whom it never was intended, either by the founders, or by those liberal individuals who have contributed to the support of an Institution, established for the purpose of furnishing at a cheap rate to the working classes, the means of instruction and amusement for their leisure hours.

Thus, Mr. Editor, you may perceive we have had a narrow escape from the vortex of gentility, that threatened at one huge gulp to have swallowed a famous library, a good stock of apparatus, sundry fossils, shells, maps, &c. &c., in short, every thing needful to commence laying the foundation of a" Society of Arts and Sciences." I will conclude this long epistle by advising the members of Mechanics' Institutions to look sharp into the MOTIVES of all who wish to change the name of their Institutions. Let them cling fast to the name, and never give way on that point while they have breath to speak or a hand to write with.

I am your's, &c..

JAMES JEFFERY,

A Member of the Bath Mechanics' Institution..

Bath, Sept. 7, 1829..

P. S. The defeated "Genteels," to make up for the mortification they suffer, are resorting to the most unmanly measures of retaliation-such as reporting that the Institution has fallen into the hands of democrats, &c., who intend to make it a political society, thereby thinking to injure ust in the estimation of our patrons. All such reports are utterly unfounded. But calumny we must expect: our enemies can wield no other weapon.

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MESSRS. COPE AND SHERWIN'S NEW PRINTING-PRESS.

(From a Correspondent.)

The improvements made in the printing-press, since Lord Stanhope introduced his iron one, instead of the cumbrous old wooden press, have been so numerous and important, that one might suppose it had been at length rendered as perfect as possible. Every day, however, continues to produce some new press, newer and better than the one that preceded it. Nor is this to be wondered at, when it is considered that of all engines this is by far the most important-and that the liveliest interest necessarily attaches to every device, which promises in the slightest degree to accelerate its operations, or multiply its power.

Of the new presses of the present time, that of Messrs. Cope and Sherwin is not, it is conceived, exceeded by any in efficiency. It is neat and elegant in its appearance, peculiarly simple in its construction, and possesses in perfection the qualities of working with ease and accuracy of

impression. Its working powers depend upon a combination of levers in their most simple form; the friction consequently is extremely small, and the parts can scarcely be deranged until the materials themselves shall be worked out. Instead of the large weight attached to the Stanhope and some other presses, and of the levers with weights employed for the purpose of lifting the platen and causing a return of the bar-handle, powerful springs are placed under the top of the press, which, while they give security and strength, add much to the beauty of the machine. A mode has been also introduced of adjusting the pull from the lightest required, to the heaviest that need be given, namely, by means of a wedge attached to the small screw fixed to the piston in the front of the press, which entirely obviates the necessity of unscrewing the platten bolts to introduce a thickness of card, tin, &c. between the platten and the piston. The oiling of the press, moreover, which is usually a most unpleasant, troublesome, and tedious job, (requiring in some instances as much as half a day) has

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SILVERING CLOCK DIALS.

SIR, In a No. of your valuable Magazine I saw an inquiry for the best mode of silvering clock dials, and hav ing tried a plan which has proved successful, I send you an account thereof for insertion at your convenience.

How to make the Silvering. Take of silver or gold lace an oz.; add thereto one ounce of double refined aquafortis. Put them in an earthen pot and place it over a gentle fire till all be dissolved, which will be in about five minutes; then take off the pot and add to the solution a pint of clear water, after which, pour the mixture into another clear vessel, to free it from grit or sediment. Add now a spoonful of salt; the green water will immediately let go the silvering, and the particles will form themselves into a white curd; then pour off the water and throw it away. The white curd must be mixed with two ounces of cream of tartar, half an ounce of whiteing, and a large spoonful of salt, more or less according as you find it for strength. Mix it well together, and it is fit for use.

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Sir,-Some months ago, while reflecting on the various contrivances suggested in the Mechanics' Magazine, for rescuing the inhabitants from houses on fire, I formed the plan of one in my own mind, which was forgotten, in consequence of other engagements, until a few days ago, when I received your 300th Number, containing one, in some respects, similar to my own. But as I still think my own plan better than that of Mr. Gregory's, or any other which I have yet seen described; and as any hint

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