tronomy by an eclipse of the sun on
August 21st, 1560, which was total in some parts of Europe. Astonished
that such a phenomenon could be predicted, he devoted himself to a study
of the methods of observation and calculation by which the prediction
was made. In 1576 the King of Denmark founded the celebrated observatory
of Uraniborg, at which Tycho spent twenty years assiduously engaged in
observations of the positions of the heavenly bodies with the best
instruments that could then be made. This was just before the invention
of the telescope, so that the astronomer could not avail himself of that
powerful instrument. Consequently, his observations were superseded by
the improved ones of the centuries following, and their celebrity and
importance are principally due to their having afforded Kepler the means
of discovering his celebrated laws of planetary motion."

The direction of the telescope to the skies by Galileo gave a wonderful
impulse to the study of the heavenly bodies. This extraordinary man is
prominent in the history of astronomy, not alone for his connection with
this supreme invention, but also for his achievements in the more
abstract parts of astronomy. He was born at Pisa in 1564, and in 1609
the first telescope used for astronomical observation was constructed.
Galileo died in 1642, the year in which Newton was born. It was Galileo
who laid with solidity the foundations of that science of Dynamics, of
which astronomy is the most splendid illustration; and it was he who, by
promulgating the doctrines taught by Copernicus, incurred the wrath of
the Inquisition.

The structure of the human eye in so far as the exquisite adaptation of
the pupil is concerned presents us with an apt illustration of the
principle of the telescope. To see an object, it is necessary that the
light from it should enter the eye. The portal through which the light
is admitted is the pupil. In daytime, when the light is brilliant, the
iris decreases the size of the pupil, and thus prevents too much light
from entering. At night, or whenever the light is scarce, the eye often
requires to grasp all it can. The pupil then expands; more and more
light is admitted according as the pupil grows larger. The illumination
of the image on the retina is thus effectively controlled in accordance
with the requirements of vision.

A star transmits to us its feeble rays of light, and from those rays
the image is formed. Even with the most widel