124 ELEMENTS OF SCIENCE 



attract, while those flowing in opposite directions repel 

 each other. 



Heat and electricity have very definite relations, and 

 a multitude of more or less recent investigations have 

 enriched the thermal section of electrical science. Here 

 it must suffice to say that if certain metals are heated 

 unequally, an electrical current from the hotter portion of 

 the metal to the colder, and from the colder to the hotter 

 (if there is an uninterrupted metallic circuit), will be set 

 up. ' A current may also be set up in a circuit of conduct- 

 ing material by the application of heat to one part of it, 

 provided the heat be so applied that it does not diminish 

 symmetrically on each side of the portion most heated. 

 Thus the motion of heat produces electricity, and (as 

 we have seen with respect to electric currents) the 

 motion of electricity, so to speak, produces heat and 

 may produce light. 



Some further effects of electricity and its relations 

 with chemical energy, will be noticed towards the close 

 of this chapter. 



MAGNETISM. The common horse-shoe magnet, with 

 which many children are familiar, consists of a bar of 

 steel bent so that its two ends come near each other. 

 It has a slight action on certain substances, probably 

 some action (to us as yet imperceptible), on all bodies in 

 its vicinity, but a great and conspicuous effect on steel 

 and iron. Needles, iron filings and other small iron 

 bodies are attracted to, and will rise and join, such a 

 magnet when its ends are held near them. If a variety 

 .of small bodies sand, cinders, small fragments of wood, 

 tiny bits of silver and iron filings be all mixed together, 

 such a magnet will readily separate out the iron particles, 

 which will cling in bunches to its two ends. Even if the 



