122 ELECTRICITY. 



to pass from the cylinder to the jet, but the gas 

 did not light.] Ah ! the gas did not light, but 

 you saw the spark; there is perhaps some draught 

 in the room which blew the gas on one side, or 

 else it would light ; we will try this experiment 

 afterwards. You see from the spark that I can 

 transfer the power from the machine to this 

 cylinder, and then carry it away and give it to 

 some other body. You know very well as a 

 matter of experiment that we can transfer the 

 power of heat from one thing to another ; for if 

 I put my hand near the fire it becomes hot. I 

 can show you this by placing before us this ball 

 which has just been brought red-hot from the 

 fire. If I press this wire to it some of the heat 

 will be transferred from the ball, and I have 

 only now to touch this piece of gun-cotton with 

 the hot wire and you see how I can transfer the 

 heat from the ball to the wire and from the 

 wire to the cotton. So you see that some 

 powers are transferable and others are not. Ob- 

 serve how long the heat stops in this ball. I 

 might touch it with the wire, or with my finger, 

 and if I did so quickly, I should merely burn 

 the surface of the skin ; whereas if I touch that 

 cylinder, however rapidly, with my finger, the 



