332 THE CAUSES OF THE — xT 
notion of the nature of the forces exercised by 
living beings, we discovered that they—if not 
capable of being subjected to the same minute 
analysis as the constituents of those beings them- 
selves—that they were correlative with—that they 
were the equivalents of the forces of imorganie 
nature—that they were, in the sense in which the 
term is now used, convertible with them. That was 
our general result. . 
And now, leaving the Present, I must endeavour 
in the same manner to put before you the facts 
that are to be discovered in the Past history of 
the living world, in the past conditions of organic 
nature. We have, to-night, to deal with the facts 
of that history—a history involving periods of 
time before which our mere human records sink 
into utter insignificance—a history the variety and 
physical magnitude of whose events cannot even 
be foreshadowed by the history of human life and 
human phenomena—a history of the most varied 
and complex character. | 
We must deal with the history, then, in the 
first place, as we should deal with all other 
histories. The historical student knows that his - 
first business should be to inquire into the validity — 
of his evidence, and the nature of the record in — 
which the evidence is contained, that he may be 
able to form a proper estimate of the correctness / 
of the conclusions which have been drawn from — 
that evidence. So, here, we must pass, in the first 
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