ANNUAL SOLAIl ACTION. 



which it may be applied in the economy of nature, from 

 the consideration that while its decomposition into the 

 oxygen and hydrogen of which it is composed is the 

 most rapid, and its change into vapour is the most 

 general means of absorbing heat, or making it cease to 

 be discovered either by the senses or the thermometer ; 

 the production of it by the union of its constituent parts, 

 is the most ardent species of combustion that is known. 

 The atmosphere, too, is in change of temperature, and 

 also in electric and other changes the nature of which is 

 not so accurately known the most delicate of substances, 

 and is constantly varying its position, even at those 

 times when, to our perceptions, all seems calm and 

 tranquil. There cannot be the least variation of 

 local gravity or local heat, or the least breathing of 

 a plant or animal, or decomposition of any one sub- 

 stance, organic or inorganic, without a change in the 

 atmosphere ; and the changes are often so considerable 

 that they are wafted over the whole globe, and the 

 winter at the one pole helps to modify the summer 

 at the other. 



In order that the motions of the ocean and the air 

 may be more certain, more extensive, and more varied, 

 those fluids are acted upon by two distinct causes, 

 difference of heat and difference of gravitation toward 

 the celestial bodies. The general influence of the for- 

 mer follows the apparent course of the sun, in its spiral 

 progress from tropic to tropic ; the latter depends partly 

 upon the sun, but much more upon the moon. That 

 the pale, but beautiful light, which the moon lets fall, in 

 variations far more agreeable than if it were as regular 

 in its quantity and duration as that of the sun, performs 



