74 flaturc'0 /DMracles. 



ages ago by the magic of the sunbeam; and 

 the sun ? Well, we are getting close on to 

 the borders of theology, and being only scien- 

 tists we had better stop with the sun. 



Then- is still another way of generating 

 electricity besides those that \vc have named; 

 which arc friction, chemical action, and the 

 magneto-electric mode of generating a current. 

 Electricity may be p-nerated by heat. If wo 

 connect antimony and bismuth bars together 

 and apply heat at the junction of the metals 

 and then connect the free ends of the two bars 

 to a galvanometer, it will indicate a current. 

 These pairs can be multiplied, and in this way 

 increase the voltage or pressure, and, of course, 

 increase the current, if we assume that there 

 is resistance in the circuit to be overcome. If 

 there were absolutely no resistance in the cir- 

 cuit a condition we never find there would 

 be no advantage in adding on elements in 

 series. 



Substances differ in their resistance to the 

 passage of electricity the less the resistance 

 the better the conductor. The German elec- 

 trician, G. S. Ohm (1789-1854), investigated 

 this and propounded a law upon which the 

 unit for resistances is based, and this unit 

 takes his name and is called the " ohm." 



Any two metals having a difference of po- 

 tential will give the phenomena of thermo- 

 electricity. Antimony and bismuth having a 



