divided circles, so that the observers, by sighting along the
instruments, could in a rough way determine the changes in distance
between certain stars, or the height of the sun above the horizon at
the various seasons of the year. It is likely that each of the great
pyramids of Egypt was at first used as an observatory, where the
priests, who had some knowledge of astronomy, found a station for the
apparatus by which they made the observations that served as a basis
for casting the horoscope of the king.

In the progress of science and of the mechanical invention attending
its growth, a great number of inventions have been contrived which
vastly increase our vision and add inconceivably to the precision it
may attain. In fact, something like as much skill and labour has been
given to the development of those inventions which add to our learning
as to those which serve an immediate economic end. By far the greatest
of these scientific inventions are those which depend upon the lens.
By combining shaped bits of glass so as to control the direction in
which the light waves move through them, naturalists have been able to
create the telescope, which in effect may bring distant objects some
thousand times nearer to view than they are to the naked eye; and the
microscope, which so enlarges minute objects as to make them visible,
as they were not before. The result has been enormously to increase
our power of vision when applied to distant or to small objects. In
fact, for purposes of learning, it is safe to say that those tools
have altogether changed man's relation to the visible universe. The
naked eye can see at best in the part of the heavens visible from any
one point not more than thirty thousand stars. With the telescope
somewhere near a hundred million are brought within the limits of
vision. Without the help of the microscope an object a thousandth of
an inch in diameter appears as a mere point, the existence of which we