338 Dynamic Theory. 



cate of zinc or "electric calamine," boracite, cane-sugar, quartz, tar- 

 trate of potash, sulphate of quinine, and some others are pyro-electric. 

 Electricity is generated in most if not all animal tissues, and it is 

 thought vegetable tissues, too. And some animals and some vegeta- 

 bles possess specially adapted organs for storing electricity. (See 

 Chap, on Electric Organs. ) Thermo-electricity: Heat applied at the 

 junction of two dissimilar metals, causes a current across the junction. 



FIG. 145. Thermo Electrical Battery. 



A, A, A. Bars of Antimony. H. Heated end of the bars. 



B, B, B. Bars of Bismuth. C.-Cold end. 



The current travels in the direction of the arrows. If the wire 

 be cut there will be tensions at the ends, shown by the signs +, . 

 The battery can be made by any two metals arranged as in the fig. 

 If the two ends of a crystal of Tourmaline be united by a wire and 

 the crystal then heated, a current will pass through the wire, and 

 it becomes a thermo-electric battery. 

 FIG. 145. 



Contact of dissimilar metals produces electricity. In the following 

 list each metal is positive to those below it, the amount of the differ- 

 ence of potential being stated in volts: 



Diff. in Potential in volts. 



210 



Lead) 



Tin ............................... 069 



Iron .............................. 313 



Copper .............. . ......... ... . 146 



Platinum ................ . ......... 238 



Carbon ............................ 113 



The difference between two not contiguous is obtained by adding to- 

 gether all between. Thus between zinc and carbon the difference of 

 potential is 1.089 volts. 



There is a difference of potential between two dissimilar liquids when 

 brought into contact ; also between a liquid and a metal ; also between 

 a hot and a cold piece of the same metal. All chemical action produces 

 electrical action. In fact, chemical action itself is held by many chem- 

 ists to be a form of electrical action. Galvanic batteries are contriv- 

 ances for converting chemical action into current electricity or rather 

 for gathering up the electricity generated by chemical action and run- 

 ning it off into a current. To sum up " the most important agencies 

 in the production of electrification in bodies, are friction, heat, chemical 

 action, magnetism, and the contact of dissimilar substances. " ( S. P. 

 Thompson, 71.) 



Atmospheric Electricity. Professor "Vander Mensbrugghe in a memoir 

 on the application of thermo-dynamics to the study of the variations of 

 the potential of liquid surfaces, is led to a conclusion of capital impor- 

 tance to meteorology. His equations, namely, seem to prove vigorously 

 that any change in the surface of the liquid gives rise to a change of 



