APPLICABLE TO PHYSICAL SCIENCE. 295 
(204.) The power of analogy, thus so ably illus- 
trated in the case of religion, is precisely as strong 
when applied to the elucidation and confirmation 
of a theory in physical science. When once what 
is supposed to be a general law of nature is dis- 
covered, its truth and certainty becomes more and 
more confirmed, in proportion to the variety and 
severity of the tests applied to it. And if, after 
tracing it, as widely as possible, through the almost 
numberless groups of the animal world, it becomes 
also apparent both in the vegetable and in the 
mineral kingdoms, we have all the evidence that 
human research or human wisdom can conceive, 
that our theory is sound; or, in other words, that 
we have achieved the discovery of one of those 
immutable truths which the wit of man can never 
devise, or the power of time destroy. 
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