378 NINETEENTH CENTURY. FT. m 



An interesting discovery was, however, made in 1822 by 

 Professor Seebeck, showing a possible cause of the electric 

 currents flowing from east to west. He wished to try whether 

 he could not give rise to a current of electricity in two metals 

 by merely using heat instead of acid and water. For this 

 purpose he took a half ring of copper and fastened to it a 

 bar of a metal called antimony, so that the two metals had 

 the form of a stirrup, and inside this stirrup he hung a mag- 

 netic needle, which would show if any current passed along 

 the metals. Then he heated one of the corners where the 

 metals joined, and immediately the magnet began to turn, 

 showing that an electric current was passing through the 

 copper, and back through the antimony. He tried this with 

 many other metals, and in every case when one of the parts 

 where they joined was made hotter than the rest, a current 

 of electricity was caused. This he called Thermo-electricity, 

 or electricity caused by heat, and this subject has now been 

 much more fully worked out by Peltier and Becquerel on 

 the Continent, and Sir W. Thomson, Professor Tait and 

 Clerk-Maxwell in England. Thermo-electricity gives us 

 another beautiful instance of the transformation of energy. 

 We saw in Chapter XXXV. that heat, when it disappears, 

 produces a certain definite amount of energy, which again, 

 in its turn, can appear in the form of heat ; since then we 

 have learnt that electricity gives rise to lines of magnetic 

 force, and a magnet sets up an electric current, and now 

 we have heat in its turn giving rise to an electric current, 

 while we know from the electric spark that chemical action 

 can be conveyed by electricity to great distances and then 

 made to reappear as light and heat. 



But to turn to the magnet. Seebeck's experiment sug- 

 gests a possible answer to the direction of the magnetic 

 needle to the north. Our globe is composed of different 



