770 On the Specific Gravity of Sea Water. [No 153. 



my hydrometer became useless, it had attained its maximum. If we 

 take corresponding limits north and south, for instance 18° IT south 

 and 18° 46' north, we have the specific gravities as 1029.106 : 1028.717, 

 nor will this deduction be materially affected by any error that may 

 possibly exist in the law of expansion. The withdrawal of fresh water 

 by congelation in high south latitudes is perhaps sufficient to account for 

 the fact, especially as there is probably no source of compensation — un- 

 less that of the solution of ice by the heat of volcanic fires, which would 

 I apprehend, be insufficient. The effect of the sun is only felt on the 

 outskirts of winter, and the ice that is broken up then, rather than melt- 

 ed, is drifted to the north, where the heat of the air, or perhaps rather 

 that of the water, is sufficient to dissolve it. From the two- fold cause 

 of greater density and lower temperature, are currents produced towards 

 the equator, serving to sustain that condition of the waters of the 

 ocean no doubt necessary, and therefore securely provided for, to the 

 health of organic life, marine and terrestrial. 



I am, your obedt. servant, 



J. Middleton, 

 F. G. S. 8fC. be. 

 December, 1844. 



