138 ELEMENTS OF STATIC ELECTRICITY. 



The brilliancy of the arc in the electric lamp is due 

 to the intensity of the motion, while the softer light of 

 the incandescent lamp results from a motion less intense. 

 When an electric lamp is being lighted or extinguished, 

 the change of color from white to the various shades of 

 red is evidently dependent on decrease of motion. 

 Must we not conclude then that the white light of the 

 electric spark, when the switch is closed, is due to 

 intensity of motion, and the colored light with the open 

 switch, to decrease of intensity, as in the iron bar or 

 the carbon of the electric lamp ? Or, if light and heat 

 are modes of motion, is not the evidence equally strong 

 that electricity is a mode of motion? Or may we not 

 go still farther, and say that light, heat, and electricity 

 are only different manifestations of that energy which 

 is a universal property of all matter, of which the ex- 

 periments here given are an additional proof? For in 

 the electric spark, we have light, heat, and electricity 

 combined. 



Having stated that D is usually the jar of higher 

 potential, it should be explained, that there is fre- 

 quently a temporary reversal of potential; and, when 

 this occurs, all the phenomena here described are 

 reversed also. The cause of this reversal will be ex- 

 plained in connection with the following experiment. 



DIRECT AND REVERSED ROTATION. A Topler ma- 

 chine can be charged only by revolving the smaller 

 plate in a given direction; which, in the machine 

 represented, is shown by the arrow. 



The reason is this: In order to store up electricity 

 in the Leyden jars, each carrier must pass from an 

 insulated brush, where it is charged, directly to a comb 

 connecting with a Leyden jar, before it passes to an 



