man, in making his signal, indicates in the first instance, by the upper pair of arms, of what class the number is which he is about to express. Suppose he says Class 1. No. 195: this is found, on referring to the vocabulary, to signify Abandoned by the crew.' And so of all the other classes. By the use of combinations, such as are employed in the Admiralty Semaphore, this telegraph might express any number, however large; but Lieut. Watson thinks it better to avoid the use of these combinations, as they are not necessary in a machine so comprehensive as his, whilst they make the operations much more complicated.

The signal-man at each station is continually on the look-out for signals from the next telegraph. When he sees the first signal, he makes a signal himself to show that he perceives it; and then, going to the ropes by which the machine is worked, he repeats the signal to the next station. If the message should consist of more than one signal, as is generally the case, the first is repeated before the second is made; and thus, if the message should contain nine signals, the first part of it would be in Liverpool at the time that the last part left Holyhead. Although the signal-man does not see the arms of his own telegraph move, from being in the small house immediately beneath it, yet he has not the least difficulty in operating with precision. At the end of each balliard is an iron weight, which just balances the arms; and in this weight is a bolt, which fits into holes made in the mast at those exact points where the halliard should be pulled to, in order to raise the arms to the required positions. To render the telegraphs available for communicating with vessels along the coast, the mast can be turned round, so as to present the machine broad-side to the sea.

This brings us to the system of communicating between vessels at sea and the telegraph. For this purpose a series of nine flags is used, so differently coloured as to be easily distinguishable. Each of these flags represents a number or figure,

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from 1 to 9, and three of them, displayed at once at the main-top, one above the other, will indicate any number up to 999. By hoisting a signal on the fore-mast to indicate the class, it is obvious that as many numbers can be represented as by the land telegraph. If a vessel in distress were to hoist the signal of Class IV. on the foremast, and 816 by three flags at the main-top, the signal-man at the telegraph would look at the vocabulary, and instantly find that Class IV. No. 816, was— "Has sprung a leak." No. 818, under the same class, would signify -"Leak increases, and is dangerous." The answer might be given, Class 1. No. 196-" Do not abandon the vessel;" followed by Class VII. No. 83, and Class VI. No. 334, which together signify"A steam-boat is gone to relieve the vessel in distress."

The chief purpose to which Mr. Watson's line of telegraphs is at present applied, is to report, first, the state of the wind daily at Holyhead; second, the vessels passing that place outward or homeward bound; third, the state of any vessel in distress, or in need of assistance, along the whole intervening line of coast; fourth, any important information, either political or commercial, from Ireland or America-made known in the latter case at Holyhead by the signals of homeward-bound vessels. But there are various other purposes which these telegraphs may be made to answer. The difficulty is to say what kind of correspondence they may not serve to conduct. We know not, indeed, that it will deprive the post-office of the love-letters which now pass through it, though we see no reason why it should not. On the contrary, its swiftness is admirably adapted for the communications of impatient lovers.

Therefore do nimble-pinioned doves draw 'Love's heralds should be thoughts;

love, And therefore hath the wind-swift Cupid wings.'.

So said sweet Juliet; and had she had a telegraph, it would have made

years of observation, this clock would have been perceived to be in some degree affected. Yet it has not been the case. The bells are frequently rung, and heavy gales bave occasionally damaged the fabric and the neighbouring buildings without any perceptible effect upon the performance of the clock.

That the clocks of churches vary considerably from one another as to time, I admitted; but I stated that, in repeated instances, I had traced the cause to the ignorant or negligent manner in which the clocks were kept. Mr. Wynn attributes it, in those clocks which have dials, to the action of the wind on the bands; and in those which have none, to the shaking of the towers by gales of wind and by bell-ringing; but not a single fact is adduced in proof of these assertions. On the other hand, I have adduced instances of two clocks, one with a dial exposed to the west, the other without a dial, both of which perform with great accuracy, and without being affected by the alleged concussion of the towers.

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favour of the propriety of calling a special general meeting-the op portunity such a meeting would afford of discovering who ought to pay for the repairs of the roof." The very low state of the funds of the Institution renders this point too important to be overlooked, or not to be of the very first consideration.

From the palpable disinclination evinced on the part of the constructor, or constructors, of the roof, whoever he or they may be, to give explanation of the matter, it is but fair to conclude that there is something which would ensue upon such explanation that would not be at all to his or their interest; this, however, should only make the Committee more active in finding out the real offender (if indeed he be not already known), in order that the saddle of expenses may be fitted to the right back.

* I beg leave to say that I entirely agree with your correspondent in his remarks upon the repetition of Mr. Wallis's Lectures; and also to add, that I think such garish lectures are adapted as much for the purposes of attraction and the consequent addition to the funds, as for the real instruction of its members. It is to be regretted that the Institution has placed itself in such a situation as to render such, amongst other expedients, necessary for the supply of funds for its ordinary purposes.

J. G.

LONDON MECHANICS'

INSTITUTION.

Mr. Editor,-Amongst such of your correspondents as have attended to the condition of the roof of the Lecture-room of the Mechanics' Institution, not one appears to have urged that which I should conceive to be the most cogent argument in

I am, Sir, Yours very faithfully, AURUM.

FOOTING STOCKINGS. Sir,-As Mr. Peede's inquiry (No. 217, page 221) is imperfectly answered in No. 220, of Saturday last, I shall attempt a more satisfactory one. Stockings can be refooted either by frame or knitting pins, (only stockings originally wrought by the hand, cannot be done on the frame, having no seam behind, and so cannot be opened to be fitted on it.) In Scotland this practice is quite common: the peo

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ple who do it keeping yarn of every shade and colour to match the old legs; the ordinary charge is about half the original cost of the stockings.

I am astonished bow a "Frame-work Knitter" could assert that "footing stockings on the machines would cost more trouble than making new ones. I have seen it many times done, and never saw any apparent difficulty attending it. I have little doubt but those who are expert at this very economical branch of the trade, would meet ample encouragement in London; and have scarcely a doubt, but the observations Mr. Peede's inquiry has elicited, may be improved to real advantage by some who might not be aware that such a practice had yet to be introduced into the metropolis. I am, Sir, Yours,

In lieu of Metal, let Gunter's chain be made of wood, because wood will never alter in length, either by heat or cold, wet or dry. Let the chain consist of twenty staffs, AB, BC, CD, &c. each five links long; and let it be made to open and shut by hinges C and B, &c. The end of the staffs shall touch each other, and, when shut up, they will form a body like a board. (For a great survey, the chain may be made much longer.) To measure the base line, let it be measured on ice; and if you would find the magnitude of the world, measure a line directly north or south, from some one station, to a distance of

sixteen or twenty miles, marking the ice at the end of each measure with a knife: so in the whole measure you would not be out half an inch. This measure should be performed betwixt the latitudes of forty and fifty degrees; both on account of the world being an oblate spheroid, and because ice of great extent may be found in these regions, as, for instance, about the American shores. Now, at the ends of the base so measured, observe the meridional altitude of some one fixed star, i. e. when culminating; and take the difference of those altitudes, and it will give the_angle which your measured base subtends at the earth's centre; then state, as the angle so found is to 360 degrees; so are the miles measured, to the miles on the whole meridian of the earth.

Note. The steel chain, with which the great survey in England was made, must have been about five inches longer in a hot day, than in a cold one; nor will you ever measure far enough on land correctly, by reason of its unevenness. It were as absurd to expect to do so, as to seek the distance of the sun by help of the transit of Venus over the sun's face; forgetting that you are seeking a parallax from that which of itself has a parallax, and' which, therefore, would but find those proportional distances which are otherwise known.

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