218 SECRETS OF ANIMAL LIFE 
condenses from the atmosphere, percolates through 
the soil, with the help of the associated carbon 
dioxide dissolves mineral matter, flows to the sea, 
and rises again in cloud. Thus it regulates the 
temperature of land and sea, mobilizes and dis- 
perses large quantities of elements, gives the sea 
an approximate constancy of composition, canalizes 
the earth, produces great terrestrial diversity, and 
so on. So from Professor Henderson’s panegyric 
on water as a factor in evolution we pass naturally 
to Professor Chamberlin’s emphasis on the relative 
uniformity which the meteorological cycle and 
other processes have ensured. ‘ Perhaps there is no 
fact in the earth’s career more remarkable than the 
fidelity with which the very narrow ranges of 
temperature, and the not less narrow ranges of 
atmospheric constituents essential to the evolution 
of life, have been maintained, while oscillations 
within these permissible ranges have freely pre- 
vailed. These limits and these oscillations were 
perhaps as imperative for life’s origin as for its 
prolonged maintenance.” The steadiness of the 
physico-chemical environment, which has been 
friendly to the ascent of life, is not inconsistent 
with there being a gradual change in soil and in 
climate which may have served as a spur to the 
evolution of organisms. Organic evolution has had 
its pulse, responding to ameliorating or depress- 
ing external conditions, just as our individual pulse 
responds to a sunny or a gloomy day. “ Does not 
a man,” John Burroughs said, “imply a cooler 
