80 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 (abazssement) 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; 
