72 



perate zones, the local influence of the seasons 

 would be almost nothing in it. 



Mr. Peron * who has very successfully repeat- 

 ed the experiments made by Ellis, Forster, and 

 Irvine r on the cold that prevails at the bottom of 

 the ocean, affirms, " that every where the open 

 sea is colder at noon, and warmer at night, than 

 the surrounding air." This assertion has need 

 of much restriction ; I am ignorant whether it 

 be exact in the forty-fourth and forty-ninth de- 

 grees of south latitude, where this laborious na- 

 turalist appears to have made the greatest num- 

 ber of his thermometrical observations ; but 

 between the tropics, where the air in the open 

 sea is scarcely two or three degrees colder at 

 midnight than two hours after the culmination 

 of the Sun, I have never found the least change 

 in the temperature of the ocean, either day or 

 night. This difference is sensible only in a dead 

 calm, during which the surface of the water 

 absorbs a greater mass of rays ; but we have 

 already observed, that the thermometrical expe- 

 riments made in this state of the ocean relate to 

 a local phenomenon only, and ought to be en- 

 tirely excluded in discussing a problem of ge- 

 neral physics. 

 The observations contained in the preceding 



* Annales du Museum, t. v. p. 123—148. Journ. de 

 Phys. t. lix, p. 361. Gilbert, Annalen der Physik, t. xix. p. 

 427. 



