Electrical Kite, a well-known machine, which was originally contrived to serve as a toy for children, but which has lately been applied to the more useful purpose of conducting- the electric matter of the atmosphere from the clouds.
Different kites have been constructed by Cavallo, and other philosophers; and, though such contrivances are not very difficult, yet there are some fixed principles, which ought to be observed in manufacturing electrical kites to a certain degree of perfection. To accomplish this object, we have subjoined the following cut, together with the necessary rules, extracted from a treatise published in German, by the late Professor Liqhtenberg, of Gottingen.
The body of the kite consists of a long slender lath, a, b, and a wooden bow, d, a, e. The former, must be made of slender, dry deal, properly planed, about five feet in length, one inch in breadth, and half an inch thick, so that it may neither be too heavy, nor too light to resist strong gusts of wind.
The bow d, a, e, is formed of a sound hoop, that may be taken from a dry cask; or it may consist of split cane or whalebone, rendered perfectly smooth, and of equal thickness. Particular attention, however, is requisite to adapt it to the proper size; for, if too weak, it will not be sufficiently elastic to expand the cord c, c. The dimensions of the bow must likewise be carefully adjusted to those of the lath a, b; and as the utility of the machine in a great measure depends on the accuracy of such proportions, we shall briefly state the rules by.which they may be easily ascertained.
The two ends of the bow are first to be contracted by means of the cord, which ought to be properly stretched. The middle of the bow must be exactly fitted to the lath a, so that one inch only of the latter project; and the place which is intersected by the string c, c, should be accurately marked. The lath, from this mark to its extremity b, ought to extend somewhat farther than double the length of its upper part.
Having found the proportion between the length of the lath, and the semi-circle of the bow, every thing depends upon the proper joining of these two essential parts. Hence a superficial excavation should be made at about an inch from the extremity of the lath a, and a similar cut in the centre of the bow; both are then to be brought into contact, and fastened with strong thread or silk.
The extremities of the hoop should now be made exactly of equal length ; when one end is to be tied with thin packthread to the bow at d, about half an inch from the point; and, after having; made small excavations into the lathy, on all its sides, one arm of the hoop d ought to be drawn close to the transverse piece ; the packthread twisted several times round ; and at length tied to the other arm at e Now the two sides from d to f, and from f to e, ought to be measured : if they happen to be unequal, the difference may be adjusted by pulling the thread towards the shorter side. Next, the thread is to be extended from e towards a, where it should be turned round several times; and thence conducted to d, the place in which it is fastened, so that it will form the angle d, a, e, as represented in the figure.-A small incision must far ther be made in the part of the lath marked b, to which the thread is extended in the direction from d to b, and thence again to e, where it is ultimately secured.
Thus, the skeleton of the kite will be arranged; and it now remains to ascertain its equilibrium, which may be effected in the following manner : The end of the lath projecting at a, should first be rounded by the knife, and placed on a table, when the opposite end b is to be poised on the tip of the finger. If both sides of the bow are in perfect equilibrium, the skeleton is then complete; but, if either of them incline to one side, the want of symmetry may be remedied by cutting or shaving off the preponderating side of the lath, so as to reduce it to an equipoise. The frame, thus finished, is next to be covered either with silk stuff, or thin paper previously oiled, that it may resist the effects of moisture : and to prevent folds either in the silken or paper cover, they should be wetted before they are applied., and afterwards dried in a cool place. In order to secure the whole covering to the frame, narrow slips of silk or paper should be pasted across the lath, and over the packthread in all the parts marked g; and, when the whole is perfectly dry, its equilibrium must again be adjusted, by putting such additional pieces on the light side, as may be requisite to restore the balance.
In constructing electrical kites, it is of the utmost consequence to apply the string h, h, below the body of the machine to its proper place : when the latter is five feet long, the cord ought to be eleven, one end of which should be passed through the two holes of the lath ; namely, one in the direction of the uppermost slip marked g, g, and the other through the central part of t!>e bow: then two similar holes must be perforated through the lath where the lowermost slip is denoted at g, that is, at a little distance from each other; and, after properly drawing out the string, so as to form an obtuse angle over the body of the kite, it ought to be well secured behind, and afterwards tied with a knot, exactly in the middle, to make both parts of equal length. Another difficulty might arise from the uncertainty of determining the exact point of the cord last mentioned, at which the main string governing the kite should be applied. Hence the following general rule requires attention ; namely, that, according to the impetuosity of the wind, the principal string must be fastened higher towards the head of the kite, with a view to facilitate its rising; and, on the contrary, lower towards the middle, in less blowing weather. The most advisable method will be, to tie the leading cord at a few inches only from the upper hole, and to ascertain its exact situation by experience.
The tail of the kite, k, k, now remains to be fixed, and is perhaps the most critical part of the whole machine. If it be too short, the latter instantly descends; and, if it be too long, its weight prevents the kite from rising. The most effectual way to avoid both extremes, will be to make the tail seven times the length of the frame: fine packthread should be chosen for this purpose, and double or triple folded slips of paper, two or three inches long, ought to be tied into the pendent string, at short intervals; when the latter is to be affixed to the body of the kite at b.
With respect to the flying of this machine, an open place and a fine day should be selected, when a gentle breeze agitates the air : after launching it against the wind, the person who holds the string ought to advance speedily to the distance of thirty or forty yards; and gradually to relax the whole clue, accordingly as the rising is more or less rapid. In order to adapt kites to the attraction of lightning jrom the clouds, a thin metallic point is to be affixed to the highest end a and connected with the string of the machine by means of a thin wire : In this application, however, the greatest caution is necessary; and those, who amuse themselves with experiments of such precarious nature, ought by no means to make the first attempt during thunder-storms, but only when the sky is serene: nor should any person affix a metallic point, or wind the wire round the string, or even moisten it, unless he be perfectly acquainted with the principles on which their joint action depends. Hence, smaller kites which do not ascend too high, must be first employed, till we become better acquainted with the rules of flying, and of fastening the machinery ; thus, every danger may be obviated, and this apparently puerile contrivance, be rendered subservient to a very useful purpose.- The necessary directions for managing electrical kites, as well as the most proper conduct at the approach of, and during a thunder-storm, the reader will find under the articles Lightning and Thunder.