SCIENCE OF COMMON THINGS. 



Aurora-borealis occurs In the day-time. TThat is galvanism ? 



the telegraph ; and as the effects upon these instruments 

 are noticed by day as well as by night, there can be no 

 doubt of the occurrence of the aurora at all hours. The 

 intense light of the sun renders the auroral light in- 

 visible during the day. 



1385 Of what utility are the auroral appearances in the polar regions ? 



During the long polar night, when the sun is absent, 

 the aurora appears with a magnificence unknown in 

 other regions, and affords light sufficient for many of 

 the ordinary out-door employments. 



CIIAPTEE II. 



GALVANISM. 



1886 What is galvanism ? 



It is the production of electrical disturbance by chemi- 

 cal action. 



1887* What is the most simple manner of illustrating the production of 

 this electricity? 



If we place a piece of silver on the tongue, and a 

 piece of zinc underneath it, no effect will be produced 

 as long as the two metals are kept asunder ; but when 

 their ends are brought together, a distinct thrill will 

 pass through the tongue, a metallic taste will diffuse 

 itself, and, if the eyes are closed, a sensation of light 

 will be evident at the same moment. 



1888 To what is this result owing f 



To a chemical action developed the moment the two 

 metals touched each other. 



The saliva of the tongue oxidizes a portion of the zmc, which excites 

 electricity, for no chemical action ever takes place without producing elec- 

 tricity. Upon bringing the ends of the two metals together, a slight 

 current passes from one to the other. 



1889 By whom was the production of galvanic electricity first noticed t 



