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DESCRIPTION. Let KL be the base of the stand, it to a sliding piece, Za is then ca. to be placed on the top of a pedes, pable of sliding in an inlet groove, tal parallel to the horizon, by the side OP, supported by hinges at Sand T; of which the arm, NU, is to act. whence, taking hold of the arm at V,

AB is a trough to contain the tele- and sliding it toward or from P, Za scope; at its end, A, a piece of plank will have an horizontal movement, hy. or board, GH, is made fast, and is which the telescope and trough, AB, fixed to the base by two hinges, E and will be elevated or depressed, and with R. Near the top of the trough, the a beautiful slow movement. arm, NU, is so fixed, by an extended As for the horizontal range, or for pin, de, as to play in diverse direc- turning the whole to any azimuth, the tions. The arm, NU, is to slide in the operation is so simple as to require no tube, w, and to be made fast at any explanation. desired part by turning the screw at Ý The telescope thus supported, and until it presses against the arm, and the pedestal resting on sand, I have by this means you will fix it very nearly found by experience that nothing will to any desired altitude.

disturb it but the wind. Now one side of the tube, W, being NOTE.-To all telescopes of great made to project, and a hole, X, made power it is better to have two finders, through it for the purpose of screwing the one of a great field of view.



it is greater than the angl. AFD MATHEMATICAL CASE.

(Prop 32, Book 1.); but the greater SIR,In page 374 I find the angle of any triangle is subtended question-" Can a straight line by the greater side (Prop. 19, Book 1.), touch the circumference of a circle therefore DF is greater than DA; in any point at a less angle than 900, now DA is equal to DC, therefore with the radius drawn from that DF is greater than DC, and the point to the centre?" I am inclined point F is therefore without the cir. to doubt the correctness of the con- cle. And F is any point whatever in clusion drawn by your plural Corthe line AE, therefore AE falls respondents, “ Discipuli.” It ap. without the circle. pears feasible at the first “ dip;" but I think, if the “bucket" be allowed to sink a little deeper, a different conclusion will be drawn.

After a careful investigation of those particular propositions of Euclid which bear upon the point in question, I see no reason to doubt the correctness of the conclusions which Euclid has drawn, and which are the reverse of the one drawn by the “ Discipuli.” As some of your readers may not have Euclid to refer to, I will quote his 16th Proposition, Book ill., which bears directly on this point.

"The straight line drawn at right " Again, between the straight angles to the diameter of a circle from line, AE, and the circumference, no the erlremity of it falls without the straight line can be drawn from the circle; and no straight line can be point A which does not cut the cirdrawn between that straight line and cle. Let AG be drawn in the angle the circumference, from the extremity DAE; from D draw DH at right of the diameter, so as not to cut the angles to AG; and because the angle circle.

DHA is a right angle, and the angle ro Let ABC be a circle, the centre DAH less than a right angle, the of which is D, and the diameter side DH of the triangle DAH is less AB; and let AE be drawn from A than the side DA.(Prop. 19, Book 1.) perpendicular to AB, and AE shall The point H is therefore within the fall without the circle.

circle, and therefore the straight line AG cuts the circle.

“ Cor.-Hence it is manifest, that the straight line which is drawn at right angles to the diameter of a circle from the extremity of it touches the circle, and that it touches it only in one point; because, if it did meet the circle in two, it would fall within it. (Prop. 2, Book 111.) Also it is evident that there can be but one straight line which touches the circle in the same point.”- Playfair's Geometry.

This conclusion appears to me de

cisive. Suppose the line AG at the " In AE take any point, F; join smallest imaginable distance from DF. and let DF meet the circle in AE, still a line drawn from D, meetC. Because DAF is a right angle, ing AG at right angles, will form a

SECRETS IN SELLING-SIR H. Dave's correr SHEATHING. 427 right - angled triangle, DAH, of SIR H. DAVY'S. COPPER SHEATHING, which DA (the hypothenuse) will The following paragraph from the be the greater side; and, therefore, Plumouth Jour'nul has. during the DH is less than DA, and within the past month, gone the round of all circumference; and (by Prop. 2, the newspa

Top the newspapers :Book in.) AE cuts thc circumference in two places.

Failure of Sir H. Dave's Plan for the

Protection of Ships' Bottoms. Your Correspondent (or dents).

“ The plan some time since re, will not need to be reminded, that a mathematical point or line is not

commended by Sir H. Davy, to pre

vent the oridation of copper on ships' such as to be seen by the naked eye, nor even by the best microscopes.

bottoms, and which was adopted by The points and lines in a diagram

Government, with a laudable zeal

for the interest of science, has not are seen, but they are merely a guide

been found to produce the expected to the inward or mental view. In

benefits. In the instance of one of such questions as the above, we must

his Majesty's ships, which was fitted first draw lines at perceptible distances; and if we want to draw couclusions

four years ago upon Sir H. Davy's

plan, and which is now undergoing from imperceptible distances, we

repair in this dock-yard, it appears must carry on the operation men

that the galvanic influence of the tally, from the facts deduced at per

iron has indeed prevented the oxiceptible distances.

dation of the copper, but the bottom I am, Sir, .

of the ship is found, as in the case Yours respectfully, of wood-sheathing, to be foul with

R. H. weeds and barnucles, to provide

against which, copper bottoms were

originally adopted. We understand . We have also received answers that orders have been received to ad Discipulos from Amicus, Acute discontinue the fitting of his MaAngle, Napier, B., J.P.G., F.O.M., jesty's ships upon Sir Humphry and Zero, one or more of which we Davy's principle.” shall (probably) give in our next.- We deferred copying this (appa

rently exaggerated) statement into

our publication, until we should SECRETS IN SELLING.

see what answer or explanation it

would draw forth from the learned · Sir, I am afraid C. M. willstill find President of the Royal Society, or hiinself a little in the mist, notwith- his friends. In the Annals of Phi, standing the ingenious solution given losophy for the present month (Oc. by F.O.M., page 381, for how he is tober), Mr. Children has given the to find the value of 0 from the two explanation for which we waited. It heights of the barometer ? I shall appears from this, that Government propose the following question to be have not abandoned Sir H. Davy's solved from F. (). M.'s formula : - plan ultogether; that the application Suppose a cubic foot of cork exactly of his protectors is merely suspended balances 241 ounces avoirdupois of for sea-goiny ships; and that it is orlead, when the barometer stands at dered to be applied to all ships in 280, what will be the weight of the good condition in ordinary (the same piece of cork when the baro- Royal Sovereign, for instance), as meter stands at 31°, the temperature also to stationary ships, such as of the air in both cases being 55° ? sheer-hulks, receiving-ships, &c.I am, Sir,

Mr. Children adds the following reYours respectfully,

marks, in the spirit of which we

" It is not for us to question the P.S. Mr. F.O. M. does not show propriety of the measures adopted what correction should be made on by the Lords Commissioners of the account of difference of temperature. Admiralty, though we cannot help



fully concur:


PERPETUAL MOTION. still thinking, that'hy a due adjust. posite direction-thus the two errors ment of the proportion of the pro- compensate each other; and by tecting to that of the copper surface, dividing the time between the stars the 'inode mày yet be found perfectly appearing on the 1st and 5th, and on applicable to sea-going ships, as well the 2nd and 4th wires, we get the as those in ordinary. It seems to error of collimation--this is, “si us to be one of those cases in which rite audita recordor,” the principle the iheory is so obviously correct, of Mr. South's method. What Mr. that whatever difficulties may occur F. Ford does not understand is, how in the earlier attempts to reduce the the telescope can be instantaneously method to practice, there must be reversed. My answer to this is, that certain circumstances which, when it is not done instantaneously, nor is once discovered, will ensure com- it necessary that it should : the inplete success. What those circum- strument, in order to perform this stances are, can only be determined operation, must have an azimuth by reflection and experiment. Sir as well as a vertical motion, and the Humphry Davy has already done time in which the star passes from much; and we do hope that every one wire to the next (which time, it facility will be offered him for con- is possible, may be increased by the tinuing and perfecting his labours error of collimation itself, the teleon this nationally momentous sub- scope being reversed), is, I take it, ject. He has victoriously contended sutticient for this operation. Your with difficulties far grcater, in our Correspondent will ask how a mural estimation, than any that await him circle, which has no azimuth motion, in this investigation, and we confi- can be corrected for collimation? dently predict that his keen and in the answer, I believe, will be, that defatigable genius will ultimately tri- in this case a zenith sector will be umph over every present obstacle.” necessary, having motion in azi

muth (as I believe they all have) to find the error of collimation in the

circle; for if an observation be taken SOUTH'S COLLINATION ADJUST

in the same observatory, at the same MENT.

time, on the same star, the only difSir; -As Mr. South's Method of ference which can arise is from the finding the Error of Collimation does collimation, refraction and all other not, as far as I can recollect, differ corrections applying equally to both. much from that which is commonly Sometimes, when the error of the used, I take the liberty of endea- clock is accurately found from other vouring to answer Mr. F. Ford's ob- observations, the mural circle is itjection, but shall feel obliged to any self moved. For any more explanaone who would correct me if I am tion on this subject, I beg to refer in error.

Mr. F. F. to Mr. Woodhouse's The line of collimation is the line Astronomy, vol. 1. part 1., chap. 5.. joining the principal focus of the

"I remain, Sir, "object-glass with the centre of the Yours inost respectfully,

O F. O. M. wire of the telescope should be Nottingham, September 25th. 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 oh. PERPETUAL MOTION. ' served, and the instrument be moved Sir,-A few years since, having through 180 deg. azimuth, and the read a 'Treatise on Mechanical Powers, telescope be made to revolve back by Bishop Wilkins (having never through an arc equal to twice the zenith distance of the star, it will be before thought for a moment on such again directed to the star, and what. a subject), I was, as it were, struck ever error took place before in one duinl) with admiration and astonishdirection now takes place in the op. inent. My mind being thus highly


429 excited, no wonder that I soon . It is, Sir, purely owing to accident felt desperately enamoured of that that I presume to intrude at all on “ chaste wanton,” the Perpetual your notice. A few days since, Motion.' But, to tell the truth, this having heard of the fame of your same chaste lady teazed me sadly for truly valuable Magazine, I purchased some time with many a wanton and it, and really found it a most delivexatious, trick ; often, as I just cious feast ; but was not a little thought I had her firm and fast, the alarmed at finding that one of your mask fell, and, behold; 'twas but ingenious Correspondents had very a phantom. However, like a true nearly pounced upon my favourite lover, I still pursued, and am now hobby-horse-I mean the gentleman happy to say that my endeavours are who made the short leg of the syphon crowned with perfect success. By discharge water by blowing over the dint of assiduous perseverance I mouth of it with a bellows. Had have, at last, overcome every scruple be gone a single step farther, and of this heretofore very coy lady, and clapt up the wheel instead of the now possess her in her most charm- bellows, farewell to the long-cheing simplicity.

rished hope of having my name . Now, Mr. Editor, if you have any handed down to posterity as the incuriosity to know “what she is like,” ventor of the first real perpetual please read the following:- To speak motion. Therefore, Sir, to prevent in plain terms, this perpetual motion such a sad mischance, if this subject is produced by means of a cistern of is not now grown too unfashionable water, syphon, and water-wheel for your pages, I shall feel highly · Respecting the particular con obliged by allowing it a corner. struction of the wheel, or the exact

I am, Sir, shape of the syphon's mouth, I need Your most obedient servant, not at present be too minute. Suffice

G. V. G. it to say that the wheel is undershot, (We must disclaim having given any and in revolving completely re. sauction to the display with which this

ingenious article has been honoured. moves the pressure of the air from

On making inquiry of the Printer's the mouth of the syphon, which' Devil, as to the reason of it, he asked, otherwise could not work, it being simply enough, “ If it was not true. the shortest leg. The water dis

then, that this was the grand perpe

tual motion discovered at last?"-ED. charged on the wheel returns again to supply the cistern, and so on per

Sir, — Having, more than twelve

months since, attempted a continued petually, in one eternal round.

or perpetual motion, precisely on the Any gentleman or lady, that pleases, same plan as that suggested by Mr. T. may have a small one made of gold,

Bell, in the 109th Number of the

Mechanics' Magazine, I think it but or any other metal they like best, fair to mention the circumstance, and with quicksilver fluid, to stand in a at the same time give my reasons why glass case on the parlour-table.

I do not think it would succeed..

The experiment I made was with a I would have published this dis number of corks, strung at intervals covery long before this time, were it for the purpose, and passed through not that I was endeavouring to have an aperture in the bottom of a glass a handsome one fitted up, with a

vessel, to which they were fitted. As

night be expected, the weight of the novel specimen of clock-work erected column of water over the aperture was thereon, and which I intended to superior to the huoyancy of the corks,

and upon their being pressed upwards have presented before the Society of

they were forced back again to the aperture. This to me was sufficient;

Arts. ;

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