with a moveable arm on its upper part (nearly resembling in shape the letter F), so as to move on a pivot. If the height of the beam above ground be six feet, the arm requires to be two feet, or in a similar proportion, adapted to the length of the former. Near the extremity of the arm, a large stone, weighing from 7 to 14lbs. should be suspended by means of a strong rope, so that it may balance about six inches from the ground. When the wind has sufficient strength to carry the kite, the main string, by which it is conducted, should be fastened to this stone, and part of the former be allowed to remain on the soil. By such contrivance, the assistance of any person for directing the machine is rendered unnecessary; as the stone, depending on the moveable arm before alluded to, will yield to the different movements of the kite. Thus, when a thunder-cloud happens to hover above the apparatus, and the electric matter finds a conductor in the metallic point attached to the top of the drake (see vol. iii. p. 53), all violent explosions will be obviated, and such dangerous fluid will quietly glide down along the wire connected with the string, till it spend itself in the ground.
As, however, this method of conducting the electric fluid is attended with considerabie danger, if managed by unskilful hands, we think it our duty to suggest an additional precautionary measure, by which the whole may be regulated with perfect security to the person thus employed. After the main string of the kite (which ought to be from two to three hundred yards long) has been fastened to the stone in the manner above directed, its extremity ought to be extended on the ground: the other end of the leading-string should be previously passed through a small roller or pulley, connected with a ring, to which must be tied; 1. a silk cord coated with wax; and, 2, a small metallic chain of such length, that it may, when the kite is rising, touch the ground at the distance of 20 or 30 paces. Now the machine is suffered to ascend, till it begin to draw the main string; when the silk cord is allowed gradually to pass through the hand, till the chain, suspended on the ring of the pulley, be at a proper distance. Next, as the body of the drake rises, the operator ought to advance progressively towards the end of the string fixed to the stone, till at length the principal cord becomes completely distended. In this state of the machinery, the farther regulation may be safely entrusted to the balance of the stone, with its moveable arm turning on the pivot of the beam before described: by means of the waxed silk cord, the manager will be protected from the influence of the electric fluid gliding down the main string, while the metallic chain will afford security against accidental lightning. And, in order to promote the derivation of this fluid from the leading string of the machine, it will be advisable to connect another chain with the extremity of such string, projecting from the stone contiguous to the beam, so that it may thus be easily conducted into the ground, in the manner similar to that already pointed out, vol. ii. p. 48.
It has been remarked, by accurate observers, that the noise of thunder is not experienced oftener than 16 or 18 times in the year, at any fixed flace. This phenome-
