EXPERIMENTS WITH THE TOPLER MACHIN ^1 ' 







Witli the switch closed, reducing the resistance Below 

 to zero, the discharge through the air is instantaneoufc^V/ 

 and there is seldom any subdivision, except that a long 

 spark from a heavy charge sometimes divides into two, 

 slightly separated during a part of their course. But, 

 with the switch open, the high resistance retards the 

 lower discharge, which is compelled to force its way 

 slowly through the kiln-dried wood; making the 

 change of potential between the outside coatings slow 

 and gradual, and producing a similar effect on the 

 inside coatings. Now, as the spark is caused by the 

 electricity forcing its way through the air, whose elec- 

 trified molecules are at the same potential near each 

 electrode, and hence self-repellent, while the surround- 

 ing air is at a lower potential and attractive, these 

 forces, acting in part at right angles to the original 

 impulse, during the comparatively slow progress of 

 the discharge, produce the brushes of diverging rays 

 already described. Various influences, such as currents 

 of air, particles of dust, and the induction of electricity 

 generated on adjacent parts of the machine, curve and 

 contort the spark, producing the peculiar phenomena 

 already described in connection with the brushes, and 

 also affecting the long blight sparks in a similar manner. 



We next notice the color of the spark. Light is a 

 mode of motion, and its color is influenced by the 

 intensity of the motion. A bar of iron, dra.wn from the 

 furnace, ready for rolling or welding, is said to be at a 

 white heat; as it cools it changes to a red heat. Here 

 the color of the light depends on heat, which is also a 

 mode of motion ; and as the intensity of the heat mo- 

 tion decreases, the light changes from white to red of 

 various shades, till the bar resumes its original color. 



