12 



On the Temperature and Saltness of 



shown by M. Ermann that salt water having a specific gravity of 1.027, 

 the mean of that of the sea, diminishes in bulk gradually down to 

 25° F., and does not reach its maximum density before congelation. 

 M. Ermann's experiments on this contraction extended from 59° F. 

 to 25°, M. Lenz extended them up to 86°, and thence deduced a 

 law for reducing the specific gravity at any one temperature to what 

 it would be at any other. The following table exhibits the specific 

 gravity corrected to the temperature of 63.5° F., distilled water at 

 that temperature being reckoned unity. 



From this table we see that in the experiments No. 1 and 4 the 

 specific gravity of sea water towards the bottom is a little greater 

 than at the surface, but that the contrary holds in Nos. 2, 3, and 5. 

 In experiment 7 the specific gravity of the surface differs so little 

 from that of the bottom that we may consider them as equal. For 

 the first two cases we may suppose that a rapid evaporation had at 

 that time determined the slight increase of density at the surface, as 

 abundant rains may have diminished it in experiments 2, 3, and 5. 

 It is remarkable that in the same place the specific gravities are al- 

 most exactly the same for different depths, if we except that of the 

 surface. No. 6 alone offers a striking exception, giving at the depth 

 of a thousand fathoms a specific gravity much less than at the sur- 

 face. We cannot suppose this difference to be due to an error of 

 observation, the specific gravity at the bottom being the mean of 

 three observations agreeing with each other, and that of the surface 

 corresponding with the observations of the day before and the day 

 after. The irregularity may perhaps be due to a current of colder 

 and less salt water flowing at the bottom from the pole to the equa- 

 tor, — a point, however, which can be determined only by repeated 



