upon the Magnetic Susceptibility of Nickel. 



137 



beneath the tongue, and in a few seconds the heat of the 

 flame temporarily destroys the magnetic quality of the nickel, 

 so that the magnet can no longer hold it. The boh accord- 

 ingly falls back and performs an oscillation. In the course 

 of its excursion, however, the metal becomes cooler, and 

 when it returns to the neighbourhood of the magnet the 

 tongue is once more attracted. But after a momentary contact 

 it is again liberated, and the process is repeated. If the 

 position of the magnet and the size of the flame are properly 

 adjusted, and care is taken to shield the apparatus from 

 currents of air, the bob may be kept swinging for an in- 

 definite period like the pendulum of a clock. 



The apparatus is shown in the annexed figure, and its 

 dimensions are as follows : — Diameter of the copper bob 

 5 centim., thickness O08 centim. Length of the projecting 



