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development it is more than ever essential
to follow the dictum of Tycho Brahe–not to
make theories until all the necessary facts
are obtained. The great astronomers of to-
day still hold to Sir Isaac Newton’s decla-
ration, ”Hypotheses non fingo.” Each one
may have his suspicions of a theory to guide
him in a course of observation, and may
call it a working hypothesis. But the cau-
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