8o LAMARCK, HIS LIFE AND WORK 



vesting crops, and other enterprises dependent on 

 good weather. 



Lamarck thus explained the principles on which 

 he based his probabilities : Two kinds of causes, he 

 says, displace the fluids which compose the atmos- 

 phere, some being variable and irregular, others con- 

 stant, whose action is subject to progressive and 

 fixed laws. 



Between the tropics constant causes exercise an 

 action so considerable that the irregular effects of vari- 

 able causes are there in some degree lost ; hence result 

 the prevailing winds which in these climates become 

 established and change at determinate epochs. 



Beyond the tropics, and especially toward the 

 middle of the temperate zones, variable causes pre- 

 dominate. We can, however, still discover there the 

 effects of the action of constant causes, though much 

 weakened ; we can assign them the principal epochs, 

 and in a great number of cases make this knowledge 

 turn to our profit. It is in the elevation and depres- 

 sion {abaissement) of the moon above and below the 

 celestial equator that we should seek for the most 

 constant of these causes. 



With his usual facility in such matters, he was not 

 long in advancing a theory, according to which the 

 atmosphere is regarded as resembling the sea, having 

 a surface, waves, and storms ; it ought likewise to 

 have a flux and reflux, for the moon ought to ex- 

 ercise the same influence upon it that it does on the 

 ocean. In the temperate and frigid zones, therefore, 

 the wind, which is only the tide of the atmosphere, 

 must depend greatly on the declination of the moon ; 



