60 On Stocking. 



The following considerations may be of use to 

 observers. Fresh water attains its greatest density 

 at 39 Fahr., and the difference from the greatest 

 density, expressed as unity, in hundred thousand 

 parts is 



Density : unity less 



Degrees Fahr. hundred thousand parts. Degrees Fahr. 

 32 

 33 

 34 

 35 

 36 

 37 

 38 

 39 



That is to say, the density of fresh water at 32 

 Fahr. is "99,987, at 39 Fahr. 1 '00,000, and at 46 

 Fahr. '99,988. 



From this it appears that the density of water 

 somewhere between 32 Fahr. and 33 Fahr. is 

 precisely the same as the density of water at 46 

 Fahr. And fluids of the same density in the same 

 vessel must occupy the same horizontal layer. 

 Therefore, at the beginning of winter, when the 

 pond water is about 46 Fahr. at the bottom, the 

 first hard frost causes the top layer to descend 

 and mix at 32, or thereabouts, with the bottom 

 layer at 46, but the difference of temperature 

 must liberate the thermal units from the warmer 

 water to raise the colder to the resulting temper- 

 ature ; in other words, force is changed from latent 



