life makes a very small addition of oxygene to the 
air, and occasions a very small consumption of car- 
bonic acid, the effect may be conceived adequate 
to the wants of nature. 
It may occur as an objection to these views, that 
if the leaves of plants purify the atmosphere, to- 
wards the end of autumn, and through the winter, 
and early spring, the air in our climates must be- 
come impure, the oxygene in it diminish, and the 
carbonic acid gas increase, which is not the case; 
but there is a very satisfactory answer to this ob- 
jection. The different parts of the atmosphere are 
constantly mixed together by winds, which when 
they are strong, move at the rate of from 60 to 100 
miles in an hour. In our winter, the south-west gales 
convey air, which has been purified by the vast 
forests and savannas of South America, and which, 
passing over the ocean, arrives in an uncontaminated 
state. The storms and tempests which often occur at 
the beginning, and towards the middle of our win- 
ter, and which generally blow from the same quarter 
of the globe, have a salutary influence. By con- 
stant agitation and motion, the equilibrium of the 
constituent parts of the atmosphere is preserved ; 
it is fitted for the purposes of life ; and those events, 
which the superstitious formerly referred to the 
wrath of heaven, or the agency of evil spirits, and 
in which they saw only disorder and confusion, are 
demonstrated, by science, to be ministrations of 
Divine Intelligence, and connected with the order 
and harmony of our system. 
I have reasoned, in a former part of this Lecture, 
against the close analogy which some persons have 
