in Fhiids. 309 



temperature, is evidently the change in the specific grav- 

 ity of those particles of the liquid which become either 

 hotter or colder than the rest of the mass, and as the 

 specific gravities of some liquids are much more changed 

 by any given change of temperature than those of others, 

 ought not this circumstance (independent of the more or 

 less perfect fluidity of the liquid) to make a sensible dif- 

 ference in the conducting power of liquids ? 



The more a liquid is expanded by any given change 

 of temperature, the more rapid will be the ascent of the 

 particles which first receive the Heat ; and as these are 

 immediately replaced by other colder particles, which, in 

 their turns, come to be heated, this must of course pro- 

 duce a rapid communication of Heat from the hot body 

 of the liquid. 



But when, on the other hand, the specific gravity of a 

 liquid is but little changed by any given change of tem- 

 perature, the motions among the particles of the liquid 

 occasioned by this change must be very sluggish, and the 

 communication of Heat of course very slow. 



Let us stop here for one moment just to ask ourselves- 

 a very interesting question. Suppose that in the general 

 arrangement of things it had been necessary to contrive 

 matters so that water should not freeze in winter, or that 

 it should not freeze but with the greatest difficulty^ very 

 slowly, and in the smallest quantity possible. How could 

 this have been most readily effected ? 



Those who are acquainted with the law of the conden- 

 sation of Water on parting with its Heat have already 

 anticipated me in these speculations ; and it does not 

 appear to me that there is anything which human saga- 

 city can fathom, within the wide-extended bounds of the 

 visible creation, which affords a more striking or more 



