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still thinking, that by a due adjustment of the proportion of the protecting to that of the copper surface, the mode may yet be found perfectly applicable to sea-going ships, as well as those in ordinary. It seems to us to be one of those cases in which the theory is so obviously correct, that whatever difficulties may occur in the earlier attempts to reduce the method to practice, there must be certain circumstances which, when once discovered, will ensure complete success. What those circumstances are, can only be determined by reflection and experiment. Sir Humphry Davy has already done much; and we do hope that every facility will be offered him for continuing and perfecting his labours on this nationally momentous subject. He has victoriously contended with difficulties far greater, in our estimation, than any that await him in this investigation, and we confidently predict that his keen and indefatigable genius will ultimately triumph over every present obstacle."

SOUTH'S COLLIMATION ADJUST

MENT.

SIR, As Mr. South's Method of finding the Error of Collimation does not, as far as I can recollect, differ much from that which is commonly used, I take the liberty of endeavouring to answer Mr. F. Ford's objection, but shall feel obliged to any one who would correct me if I am in error.

The line of collimation is the line joining the principal focus of the object-glass with the centre of the eye-glass, and in this line the middle wire of the telescope should be placed, and any error in adjustment will cause a corresponding error in time. Now, if the time of crossing the first and second wires be observed, and the instrument be moved through 180 deg. azimuth, and the telescope be made to revolve back through an arc equal to twice the zenith distance of the star, it will be again directed to the star, and whatever error took place before in one direction now takes place in the op

posite direction-thus the two errors compensate each other ; and by dividing the time between the stars appearing on the 1st and 5th, and on the 2nd and 4th wires, we get the error of collimation—this is, “si rite audita recordor," the principle of Mr. South's method. What Mr. F. Ford does not understand is, how the telescope can be instantaneously reversed. My answer to this is, that it is not done instantaneously, nor is it necessary that it should: the instrument, in order to perform this operation, must have an azimuth as well as a vertical motion, and the time in which the star passes from one wire to the next (which time, it is possible, may be increased by the error of collimation itself, the telescope being reversed), is, I take it, sufficient for this operation. Your Correspondent will ask how a mural circle, which has no azimuth motion, can be corrected for collimation? the answer, I believe, will be, that in this case a zenith sector will be necessary, having motion in azimuth (as I believe they all have) to find the error of collimation in the circle; for if an observation be taken in the same observatory, at the same time, on the same star, the only difference which can arise is from the collimation, refraction and all other corrections applying equally to both. Sometimes, when the error of the clock is accurately found from other observations, the mural circle is itself moved. For any more explanation on this subject, I beg to refer Mr. F. F. to Mr. Woodhouse's Astronomy, vol. 1. part 1., chap. 5.. I remain, Sir, Yours most respectfully, F. O. M. Nottingham, September 25th.

PERPETUAL MOTION.

SIR,-A few years since, having read a Treatise on Mechanical Powers, by Bishop Wilkins (having never before thought for a moment on such a subject), I was, as it were, struck duinb with admiration and astonishment. My mind being thus highly

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PERPETUAL MOTION.

excited, no wonder that I soon felt desperately enamoured of that "chaste wanton, the Perpetual Motion. But, to tell the truth, this same chaste lady teazed me sadly for some time with many a wanton and vexatious trick; often, as I just thought I had her firm and fast, the mask fell, and, behold, 'twas but a phantom. However, like a true lover, I still pursued, and am now happy to say that my endeavours are crowned with perfect success. By dint of assiduous perseverance I have, at last, overcome every scruple of this heretofore very coy lady, and now possess her in her most charming simplicity.

Now, Mr. Editor, if you have any curiosity to know "what she is like," please read the following:-To speak in plain terms, this perpetual motion is produced by means of a cistern of water, syphon, and water-wheel.

Respecting the particular construction of the wheel, or the exact shape of the syphon's mouth, I need not at present be too minute. Suffice it to say that the wheel is undershot, and in revolving completely removes the pressure of the air from the mouth of the syphon, which otherwise could not work, it being the shortest leg. The water discharged on the wheel returns again to supply the cistern, and so on perpetually, in one eternal round.

Any gentleman or lady, that pleases, may have a small one made of gold, or any other metal they like best, with quicksilver fluid, to stand in a glass case on the parlour-table.

I would have published this discovery long before this time, were it not that I was endeavouring to have a handsome one fitted up, with a novel specimen of clock-work erected thereon, and which I intended to have presented before the Society of Arts.

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It is, Sir, purely owing to accident that I presume to intrude at all on your notice. A few days since, having heard of the fame of your truly valuable Magazine, I purchased it, and really found it a most delicious feast; but was not a little alarmed at finding that one of your ingenious Correspondents had very nearly pounced upon my favourite hobby-horse-I mean the gentleman who made the short leg of the syphon discharge water by blowing over the mouth of it with a bellows. Had he gone a single step farther, and clapt up the wheel instead of the bellows, farewell to the long-cherished hope of having my name handed down to posterity as the inventor of the first real perpetual motion. Therefore, Sir, to prevent such a sad mischance, if this subject is not now grown too unfashionable for your pages, I shall feel highly obliged by allowing it a corner. I am, Sir,

Your most obedient servant,

G. V. G.

[We must disclaim having given any sauction to the display with which this ingenious article has been honoured. On making inquiry of the Printer's Devil, as to the reason of it, he asked, simply enough, "If it was not true, then, that this was the grand perpe

tual motion discovered at last?"-ED.

months since, attempted a continued SIR, Having, more than twelve or perpetual motion, precisely on the same plan as that suggested by Mr. T. Bell, in the 109th Number of the Mechanics' Magazine, I think it but fair to mention the circumstance, and at the same time give my reasons why I do not think it would succeed.The experiment I made was with a number of corks, strung at intervals for the purpose, and passed through an aperture in the bottom of a glass vessel, to which they were fitted. As night be expected, the weight of the column of water over the aperture was superior to the buoyancy of the corks, and upon their being pressed upwards they were forced back again to the aperture. This to me was sufficient;

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for the expansion of these corks in the manner described by Mr. Bell would, it appeared to me, not in the least increase their buoyancy, unless their bulk could also be increased at the same time.

As to the last plan alluded to by the same gentleman, it seems probable to me that a diagram I made some time since may not be dissimilar to it; but I will not attempt to anticipate his method. Should mine appear to possess an advantage over his, I will, with pleasure, send it for insertion (that having been my original intention), together with another method I have since thought of, and which is chiefly constructed on a well-known principle of hydrostatics,

Your

I remain, Sir,
very obedient servant,

G+ R.

SIR, That the little device on the subject of Perpetual Motion, which you did me the favour to insert in your 106th Number, should have been deemed by your Correspondent, under the name of T. Bell, as entitling me to be considered a young man of very promising abilities," must certainly be matter of great self-gratulation to me, and ought to be properly appreciated accordingly; and as he stretches out his fatherly hand, and smooths down the hair upon my forehead, it is only becoming me to hold down my head, and to find my youthful face appropriately suffused with the mingled blush of modesty and pride. But, Sir, old birds are not to be caught with chaff and when next your Correspondent honours me with his encomiums, I hope he will, for the sake of my "self-complacency" and his own appearance of candour, make the motive (which is so obvious in this instance) a little less apparent; for, Sir, no sooner has he finished the above eulogium, than he, the said T. Bell, "is forcibly struck (the terms in which he announces to us the design to be his own invention) that there is a better plan of applying this principle than the one described by Philo Montis." He then gives you a description of "an endless chain, a pulley, cocks, springs, and a hole in the bottom of a box;" by which apparatus, when put together, my poor, little, simple device is to be completely superseded, and taken entirely off its legs (one of which, to be sure, is rather dropsical, and the other not a little crooked). Thus, as if by magic," deprived of.

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my laurels, and with my poor device in my hand, am I to be hurled, "at one fell swoop," from "the battlements of the superstructure" on which I had planted my fondest hopes," and of the unfortunate Montis there is to be left not even so much as 66 wreck behind;" whilst the bell upon the battlements-" the mighty Tom' "who sounds so woundy great, rings, in derision, the knell of all my hopes to immortality.

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But, Sir, to the object for which I take the liberty of addressing you.Really I am not disposed to concede to Mr. Bell (who is as unknown to me as I am to him) even the merit of having devised the best of two plans, both of which are good for nothing. In the first place, the design I have given could be made to act for a time; the machine of the "better plan," I, with equal confidence, assert would never stir of itself at all. If this is true (and which, I dare say, your wellinformed Correspondent will have the fairness to acknowledge he believes would be the fact), the "better" must be considered the worst plan of the two. The defect in mine, 1 think it will be allowed, is a little observed; but the amazing resistance from friction necessary to draw a sort of contitinued piston through the hole in the bottom of the box, joined to the pressure of the superincumbent and surrounding water, as well as the friction of the pulley, never leave us for a moment able to suppose such a contrivance could act at all. I have thought of the same thing as that described by Mr. Bell before I read his account, but I should have never thought of mentioning to any one a conception, in my humble opinion, and, which it "strikes me very forcibly" to be, completely preposterous. As I have not intended really to offend in any way your well-informed Correspondent, I hope to hear from him that I have not accidentally done so, although I must still contend that my little device is as good, at least, as his great one. I am, Sir, Your obedient servant, PHILO MONTIS.

September 27th, 1825.

DIVING FISHERMEN.

There is a mode of catching fish peculiar to the Gulf of Petrasso. The fisherman being provided with

INSTRUCTION FOR MECHANICS AT PARIS.

a rope, made of a species of long grass, and which floats near the surface, has only to move his canoe where he perceives there is a rocky bottom; this done, he throws the rope out, so as to form a tolerably large circle; and such is the timid nature of the fish, that, instead of rushing out, it never attempts to pass this imaginary barrier, which acts as a talisman, but instantly descends, and endeavours to conceal itself under the rocks. Having waited a few moments till the charm has taken effect, the fisherman plunges downwards, and not unfrequently returns with four or five fish, weighing from two to six pounds each. As they seldom find more than the heads concealed, there is the less difficulty in bringing forth their rich prizes; and when the harvest is good, the divers are so dexterous, that they have a method of securing three or four fish under each arm, beside what they can take in their hands. The fish greatly resembles the John Dory.

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freezing point of mercury, if the experiments were made at a temperature a little under 32o.

POWER REQUIRED FOR DIFFERENT

VELOCITIES OF STEAM-BOATS.

We extract the following Table from a valuable paper on Steamboats, by Mr. Tredgold, in the last Number of Professor Jamieson's Edinburgh Philosophical Journal. The immense increase of power which appears to be necessary to obtain a small increase of velocity is very remarkable, and must have a great influence in inducing a preference of engines of a moderate size. The calculation applies to

still water.

Miles per

Horses' power.

hour.

3....

51

4....

13

5.

25

6..

43

7..

69

8....

..102

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REFRIGERATING SALT.

If we mix 57 parts of muriate of potash with 32 of muriate of ammonia, and 10 of nitrate of potash, a refrigerating salt will be produced. This salt, put into four parts of water, and quickly agitated, will make the thermometer descend from 20° to 5o below zero in Reaumur's thermometer.

SYNODUCED BY THE COMBINA

TION OF METALS.

According to M. Dobereiner, the fusible metal consists of one atom of lead, one of tin, and two of bismuth; and it becomes fluid when exposed to a heat of 210. If the fusible metal, formed of 118 grains of filings of tin, 207 grains of filings of lead, and 286 grains of pulverised bismuth, be incorporated in a dish of calendered paper, with 1616 grains of mercury, the temperature will instantly sink from 65° to 14o. M. Dobereiner thinks that it might sink so low as the

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INSTRUCTION FOR MECHANICS
AT PARIS.

The celebrated Baron Charles

Dupin, of the Institute, has undertaken to give instructions to the industrious classes in geometry and in mechanics, as applied to the arts. His instruction extends to the great manufactures, as well as to the most ordinary and common arts of life, and even to the fine arts. The

architect, the carpenter, the mason, the sculptor, the painter, and the engraver, each require a knowledge of certain geometrical or mechanical principles: M. Dupin supplies them with this knowledge. The knowledge he teaches is necessary to all mechanics, and artists who have any thing to do with mechanics. In soine cities of France some learned Professors have hastened to follow M. Dupin's example, and others propose to follow it.-French Paper.

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of gum mastic, and half a pint of

OIL AND GAS LAMP GLASSES FROM turpentine varnish (which may be

BURSTING.

The glass chimneys which are now in such general use, not only for oil lamps, but also for the burners of oil and coal gas, very frequently burst, owing sometimes to knots in the glass, when it is imperfectly annealed, but more frequently to an inequality of thickness at the lower end, which prevents the glass from expanding uniformly when heated. M. Cadet de Vaux informs us that, when the evil arises from the latter

cause, it may be cured by making a

cut with a diamond in the bottom of the tube. He states, that in an establishment where six lamps are lighted every day, and where this precaution was taken, there was not a single glass broken for nine years.

ANSWERS TO INQUIRIES.

NO. 147.-COLOURING BRICKS. SIR, I send you the following receipt for colouring Tiles:

Take one ounce of red lead to three ounces of manganese; get some strong clay, mix it with clean water until it is as thick as cream; pass it through a very fine sieve, then mix it with the lead and manganese. Let your tiles be dry; then pour it over them, and set them to dry. Do not let them touch each other in the setting, and keep them free from dust as much as possible in the kiln. I have only made one trial of this method, but it answered very well. To make your bricks and tiles of one colour, mix all the different sorts of clay well together.

I am, Sir,
Yours respectfully,
FRANK BUTTON,
Brickmaker.

Colston, Near Nottingham.

got for less expense at the colourshops than it can be made for, except in large quantities); put the above in a tin can, keep it in a very until dissolved; strain it, and keep warm place, frequently shaking it,

it for use. Should you find it harder you wish, you may add a little more turpentine varnish.

than

HENRY HOPE.

NOTICES

ΤΟ

CORRESPONDENTS.

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"A Real Friend," and "the circle" of friends he represents, seem to misunderstand entirely the principle on which our publication is conducted. Were we to admit nothing but what is "unquestionably correct and good," the Mechanics' Magazine would be converted into a mere repository of wellknown doctrings and precepts, instead of continuing, as it has heretofore done with so much approbation, to be the vehicle of every thing in the shape of original and ingenious speculation.

Communications received from—Experimentum-Crucis-A Mechanic-M. Welch-J. C. E.-W. S.-W. B.-Mr. Thomas-F. J-k-n-Jack Long-T.S. -A. B.-J. O.-W. C. B. P. C.-Samoht-G. S. ་T ༥.!{ཅ

***Advertisements for the Covers of the Monthly Parts must be sent to the Publishers before the 20th day of

each Month.

NO. 137.-VIOLIN VARNISH. Take half a gallon of rectified spirits of wine, to which put six ounces

Communications (post paid) to be addressed to the Editor, at the Publishers', KNIGHT and LACEY, 55, Paternoster-row, London. Printed by MILLS, JOWETT, and MILLS (late BENSLEY,) Bolt-court, Fleet-street.

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