206 SCIENTIFIC RECREATIONS. 



as big as half a pistol bullet." On a subsequent occasion he was again 

 struck senseless while endeavouring to administer a shock to a paralytic 



patient. 



It was not until June 1752 that Franklin made the experiment with 

 the kite, which resulted in such great discoveries. He made his kite of a 

 silk pocket-handkerchief, and he fixed a pointed rod upon the upright por- 

 tion of the frame at the top ; the string ended in a foot or so of silk, which 

 was held by the philosopher, and to the end of the hempen portion of the 

 string a large key was tied. For some time, notwithstanding the approach 

 of most unmistakable thunder-clouds, his patience was tried. But at last the 

 strands of the hempen string began to bristle up, and soon after, when 

 Franklin applied his knuckle to the key, a spark was obtained. The great 

 discovery was made. Franklin subsequently obtained lightning in his own 

 house, and performed several experiments with it. 



The Electroscope (fig. 211) is an instrument 

 by which we can ascertain whether electricity is 

 present or not, and the nature of it. If we bring 

 an object unelectrified close to the ball or knob 

 on the top of the glass shade, the two needles, 

 or strips of gold-leaf, which are often used, will 

 remain still. But if the body has been electrified 

 it will communicate the electricity to the rod 

 inside, and attract to itself the fluid of opposite 

 quality; the same kind of electricity then is in 

 action in the gold-leaf or needles, and they fly 

 apart repel each other. Supposing that posi- 

 tive electricity were first communicated, we can 

 cause the contraction of the leaves or wires by 

 applying a negative kind, which, meeting the 

 positive, neutralizes it, and the wires collapse. 



If the electricity with which the instrument is charged be positive, by 

 approaching the baton to the ball, A, we shall see the wires diverge more 

 than before, and they will finally be discharged by the knobs within. If the 

 electricity be contrary to that in the baton, the wires will approach each 

 other, but by gradually withdrawing the baton they will again separate, and 

 even to a greater distance than before. 



The Electric Machine is shown in the illustration (fig. 2 1 2). It consists 

 of a large plate of glass fixed upon a glass stand, between wooden supports. 

 The handle is of glass ; two pairs of rubbers are fastened above and below ; 

 the plate is turned between them, and becomes " positively " electrified. 

 The rubbers are covered with leather and stuffed with horsehair, DD, and 

 press very tightly against the glass, so that the friction is constant. The 

 rubbers are covered v/ith an amalgam made of mercury, zinc, and tin, 

 two parts of the first to one each of the others. A chain (of metal) connects 

 the machine with the ground. The conductors, PP, are united by a cross- 



