ELECTRICITY AND MAGNETISM 



cuit was formed of two wires of different metals, if 

 there be a difference in temperature at the juncture of 

 these two metals an electrical current will be estab- 

 lished. In this way heat may be transmitted directly 

 into the energy of the current without the interposi- 

 tion of the steam - engine. Batteries constructed in 

 this way are of low resistance, however, although by 

 arranging several of them in "series," currents of con- 

 siderable strength can be generated. As yet, however, 

 they are of little practical importance. 



About the middle of the century Clerk - Maxwell 

 advanced the idea that light waves were really electro- 

 magnetic waves. If this were true and light proved 

 to be simply one form of electrical energy, then the 

 same would be true of radiant heat. Maxwell ad- 

 vanced this theory, but failed to substantiate it by 

 experimental confirmation. But Dr. Heinrich Hertz, 

 a few years later, by a series of experiments, demon- 

 strated the correctness of Maxwell's surmises. What 

 are now called " Hertzian waves" are waves apparently 

 identical with light waves, but of much lower pitch or 

 period. In his experiments Hertz showed that, under 

 proper conditions, electric sparks between polished balls 

 were attended by ether waves of the same nature as those 

 of light, but of a pitch of several millions of vibrations 

 per second. These waves could be dealt with as if they 

 were light waves reflected, refracted, and polarized. 

 These are the waves that are utilized in wireless teleg- 

 raphy. 



ROENTGEN RAYS, OR X-RAYS 



In December of 1895 word came out of Germany of 

 a scientific discovery that startled the world. It came 



TOL. JII.-I7 



