CHAP. v.i. THEORETICAL DISCOVERIES IN PHYSICS. 55 



tions we term heat are the cause of the rapid motions of 

 the gaseous molecules, and that if heat was entirely ab- 

 sent the motion would cease, and ordinary cohesive 

 attraction coming into play, the molecules would fall 

 together and form a liquid or a solid. As a matter of 

 fact, by intense cold, combined with pressure, all gases 

 can be liquefied or solidified; and as, on the other hand, 

 all the solid elements can be liquefied or vaporized by 

 the intense heat of the electric furnace, we conclude that 

 all matter when entirely deprived of heat is solid, and 

 with sufficient heat becomes gaseous. 



As might be expected from these varied phenomena, 

 it has been found that there is no such sharp line of dis- 

 tinction between the various states of matter as is popu- 

 larly supposed ; some of the properties which are charac- 

 teristic of matter in one state being present in a less 

 degree in other states. Viscous bodies, for example, 

 often present phenomena characteristic of both solids 

 and fluids. Sealing-wax, pitch, and ice are all brittle at 

 low temperatures, resembling in this respect such solids 

 as glass and stone; but they are at the very same time 

 fluid, if time enough is allowed to exhibit the phe- 

 nomenon. This is seen in the motion of glaciers, which 

 move in every respect like true fluids, even to the middle 

 of the stream flowing quicker than the sides and the top 

 than the bottom. Eddies and whirls occur in glaciers 

 as in rivers, and also upward and downward motion, so 

 that rocks torn off the glacier floor may be carried up- 

 ward and deposited on surfaces hundreds of feet above 

 their place of origin. These properties can be shown 

 to exist by experiment even on a small scale. A slab of 

 ice, supported on its two ends, will become gradually 



