188 PHOSPHORESCENCE. 
electric current, we see a certain amount of electric 
vibration transformed into heat and light, for the 
wire first becomes hot and then luminous. If we 
place upon the snow two pieces of cloth—one 
white, the other black—the white one reflects back 
the heht of the sun, the dark one absorbs ‘the 
hght, and a certain amount of it is transformed 
immediately into heat, which, in its turn, is trans- 
formed into another kind of motion manifested by 
the melting of the snow under the black cloth. 
In the same way light is transformed into 
chemical action (as in photographic processes), and 
chemical action into light (combustion of phos- 
phorus). So, again, the electricity of the galvanic 
battery is transformed into its equivalent of light, 
chemical action, heat, etc., and chemical action 
gives birth to electricity, light, and heat. 
The motion or vibration of a special organic 
substance, which motion constitutes nervous force, 
can be transformed into electricity, and electricity 
into nervous force. Matteucci, who has made nu- 
merous experiments upon this subject, distinctly 
insists upon the necessity of distinguishing be- 
tween electric force and nervous force. One of 
these can give birth to the other, and reciprocally ; 
but they are not identical. When a nerve is 
excited by an electric current, it immediately oc- 
casions muscular contractions ; but at this moment 
not a trace of electricity can be detected in any 
