es? And those other, sporadic members of our system, comets
and meteors, what are they? What are their movements? How do they
originate? And the Sun itself, what is its composition, what is the
source of its heat, how did it originate? Is it running down?

These last questions introduce us to a branch of astronomy which is
concerned with the physical constitution of the stars, a study which,
not so very many years ago, may well have appeared inconceivable. But
the spectroscope enables us to answer even these questions, and the
answer opens up questions of yet greater interest. We find that the
stars can be arranged in an order of development--that there are stars
at all stages of their life-history. The main lines of the evolution of
the stellar universe can be worked out. In the sun and stars we have
furnaces with temperatures enormously high; it is in such conditions
that substances are resolved into their simplest forms, and it is thus
we are enabled to obtain a knowledge of the most primitive forms of
matter. It is in this direction that the spectroscope (which we shall
refer to immediately) has helped us so much. It is to this wonderful
instrument that we owe our knowledge of the composition of the sun and
stars, as we shall see.

"That the spectroscope will detect the millionth of a milligram of
matter, and on that account has discovered new elements, commands
our admiration; but when we find in addition that it will detect the
nature of forms of matter trillions of miles away, and moreover,
that it will measure the velocities with which these forms of matter
are moving with an absurdly small per cent. of possible error, we
can easily acquiesce in the statement that it is the greatest
instrument ever devised by the brain and hand of man."

Such are some of the questions with which modern astronomy deals. To
answer them requires the employment of instruments of almost incredible
refinement and exactitude and also the full resources of mathematical
genius. Whether astronomy be judged from the point of view of the
phenomena studied, the vast masses, the immense distances, the aeons of
time, or whether it be judged as a monument of human ingenuity,
patience, and the rarest type of genius, it is certainly one of the
grandest, as it is also one of the oldest, of the sciences.

The Solar System

In the Solar System we include all those bodies dependent on the sun
which circulate rou