When Galileo directed his telescope to the heavens, when Secchi and
Huggins studied the chemistry of the stars by means of the
spectroscope, and when Warren De la Rue set up a photoheliograph at
Kew, we see that a progress in the same direction as before, in the
evolution of our conception of the universe, was being made. Without
definite expression at any particular date, it came to be an accepted
fact that not only do earthly dynamics apply to the heavenly bodies,
but that the laws we find established here, in geology, in chemistry,
and in the laws of heat, may be extended with confidence to the
heavenly bodies. Hence arose the branch of astronomy called
astronomical physics, a science which claims a large portion of the
work of the telescope, spectroscope, and photography. In this new
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 declaration, "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 cautious astronomer does
not proclaim these to the world; and the historian is certainly not
justified in including in his record those vague speculations founded
on incomplete data which may be demolished to-morrow, and which,
however attractive they may be, often do more harm than good to the
progress of true science. Meanwhile the accumulation of facts has
been prodigious, and the revelations of the telescope and spectroscope
entrancing.



12. THE SUN.