SOLIDS, LIQUIDS, AND OASES. 



I will not now follow up this idea, but leave it as a sug- 

 gestion for the reader to work out for himself, by consider- 

 ing what would remain undone upon the earth if water 

 flowed perfectly, without any internal resistance, or friction 

 upon the earth's surface. 



The degrees of approach to perfect fluidity vary greatly 

 with different liquids. 



Is there any such a thing as an absolute solid, or a body 

 that has no degree of fluidity, the particles or parts of 

 which will admit of no change of their relative positions, 

 no movement upon each other without fracture of the mass? 

 This would constitute perfect rigidity, or the opposite to 

 fluidity. 



Take a piece of copper or soft iron wire, about one eighth 

 of an inch in diameter, or thereabouts, and bend it back- 

 wards and forwards a few times as rapidly as possible, but 

 without breaking it ; then, without loss of time, feel the 

 portion that has been bent. It is hot painfully so if 

 the experiment is smartly made. How may this be ex- 

 plained? 



It is evident that in the act of bending there must have 

 been a displacement of the relative positions of the parti- 

 cles of the metal, and the force demanded for the bending 

 indicated their resistance to this movement upon each 

 other; or, in other words, that there was friction between 

 them, or something equivalent to such internal friction, 

 and thus the mechanical force exerted in the bending was 

 converted into heat-force. 



Here, then, was fluidity, according to the above defini- 

 tion; not perfect fluidity, but fluidity attended with resist- 

 ance to flow, or what \fe have agreed' to call viscosity. But 

 water also offers such resistance to flow, or viscosity, there- 

 fore the difference between iron or copper wire and liquid 

 water as regards their fluidity is only a difference of degree, 

 and not of kind; the demarcation between solids and 

 liquids is not a broad, clearly-defined line, but a band of 

 blending shade, the depths of tint representing varying 

 degrees of viscosity. 



Multitudes of examples may be cited illustrating the 

 viscosity of bodies that we usually regard as types of solidity, 



