HEATING EFFECTS OF THE DISCHARGE. 



633 



strip of tinfoil. The glass being very slightly warmed 

 by holding it in the hand for a moment, a drop of water 

 is brought upon the point of the tube. The air in the 

 bottle has expanded by the heat of the hand, and when 

 it contracts again the drop of water passes a short dis- 

 tance into the tube. The external coating of a pretty 



FIG. 329 (k real size}. 



FIG. 330 (real size}. 



strongly charged jar is connected by a chain with the 

 ring of one of the wires, and the knob is brought quickly 

 near the ring of the other wire; the heat produced by 

 the passage of the spark through the strip of tinfoil is 

 sufficient to expand the air in the bottle again, and the 

 drop of water is pushed outwards by the expanding air 

 through a space of one or several millimetres. 



The wires in the apparatus, fig. 330, pass immediately through 

 the cork ; they need not be insnlated, for cork is by no means a 

 good conductor, and as in this experiment the charge must be pretty 

 strong, only a comparatively insignificant quantity passes through 

 the cork, while the much greater portion passes through the tinfoil, 

 which is by far the better conductor. The strip of tinfoil should not 

 be more than O mm '3 wide, it must be cut upon a support of sheet 

 metal, using a ruler and a very sharp knife, of which, if possible, 

 the cutting edge should end like that of a razor, that is, it should 



