1896.] 



on Electric Besearch at Low Temperatures. 



251 



and kept everywhere at the absolute zero of temperature, we could 

 transmit any amount of electrical energy along them without dissi- 

 pating any of it as heat in the wires. 



As a consequence of this, any pure metal cooled to the absolute 

 zero of temperature would become a perfect screen for electro- 

 magnetic radiation, and would be perfectly impenetrable to electro- 

 magnetic induction. 



We can show this increase in the ^power of electro-magnetic 



Fig. 8. 



An alternating current magnet having a coil C between its poles over which a 

 shield A of aluminium can be placed. 



screening by metals when cooled in the following way. A suitable 

 coil of wire C is placed (see Fig. 8) between the poles of an alternating 

 current magnet M, M and a small incandescent lamp L connected with 

 the coil. When the magnet is excited it induces currents in the coil 

 and the lamp glows up. A cap of aluminium A is made of such a 

 size as to drop easily over the coil. This aluminium is not of 

 sufficient thickness or conductivity to screen oft' the induction when it 

 is warm. If, however, we cool the aluminium caj) in liquid air and 



