524 PHILOSOPHICAL TRANSACTIONS. [anNO 1754. 



sufficient to prevent any thunder in town that afternoon ; though there was a 

 great appearance of thunder before the kite was raised. But whether the same 

 serenity succeeded, as frequently happens after a thunder-storm, and whether 

 there were any flashes of lightning seen in the evening, I cannot now recollect. 

 If such flashes had afterwards been seen in the skies, as is common in a sum- 

 mer's evening, especially after a thunder-storm, those might proceed from other 

 clouds, which had passed the town, at too great a distance to be acted on by 

 the kite. 



Electrified clouds have an electrical atmosphere, as well as the prime conduc- 

 tor, when it is electrified ; and the diameter of that atmosphere, caeteris paribus, 

 will. bear some proportion to the size of the cloud. My smallest prime conductor 

 is 2-i- inches in diameter ; and when it is fully charged, its atmosphere extends to 

 the distance of about 3 feet from the surface of the conductor. How great then 

 must the extent be of the atmosphere, which surrounds a large cloud fully elec- 

 trified ? It perhaps may extend to many hundreds of feet round the cloud, and 

 may even reach so low as to touch the surface of the earth : and when that is the 

 case, a man, or a rod of metal, placed on a cake of resin on the ground, may 

 be electrified, and yield sparks of fire. When a sharp point is presented to 

 that atmosphere, it cannot deprive the cloud of its whole quantity of electri- 

 city, except the sharp point be so near, that the cloud may explode upon 

 it ; and in that case the cloud must have a communication with the ground, by 

 means of some non-electric body. Suppose an electrified cloud to have an at- 

 mosphere, which extends round it to the distance of QO feet from its surface ; 

 and let that atmosphere be divided into 3 parts, a, b, and c, each 30 feet in dia- 

 meter: now if a sharp metalline point erected on a kite, or otherwise, be placed 

 either vertically or horizontally in the most interior part of the atmosphere c, 

 that point will continue to act till a quantity of the lightning is drawn ofF, equal 

 to the quantity contained in that atmosphere, arid no longer. For then the 

 semidiameter of the atmosphere being reduced to 6o feet, every part of it is 

 above, and not in contact with, the sharp point, and consequently beyond its 

 sphere of action. But let the sharp point be then advanced into the atmosphere 

 B, and it will act as before, &c. 



The truth of this, however contradictory it may be, to the general opinion of 

 the action of sharp points, in drawing oft" the electricity or lightning,* may be 

 illustrated by the following experiments on the prime conductor. Electrify the 

 prime conductor in a dark room, and draw back the globe to a sufficient distance 

 from the prime-conductor, to prevent its being supplied with any more electri- 



* Mr. Franklin says, speaking of sharp points, " At whatever distance you see the light, you may 

 draw off the electrical fire." page 2. — Orig. 



