Lecture on Astronomy.

Professor Searle delivered the third lecture of the course last night and it proved of even greater interest than the preceding ones.

The fundamental principles of physics were first developed by the consideration of the solar system.

The planets are of small dimension relative to the great distances, and the sun preponderates. They move independent as it were, the perturbations being almost imperceptible. The ancients had a general idea of the attraction of the heavenly bodies. Their speculations about the orbils were not correct. With the revival of learning in the middle ages came a renewed attention to the investigation of astronomy. Copernicus, Tycho and Kepler were the foremost students. Copernicus renewed the rejected idea that the sun was the centre of the system of planets. Tycho, a rich nobleman in Denmark, established the first observatory. Kepler investigated he careful observations and deduced the fact that the planets moved in ellipses; he established "Kepler's Laws."

Newton discovered mathematical means of expressing the law of attraction.

Centrifugal force varies as the cube +++ the distance, and gravitation varies as the square of the distance, hence two bodies tend to keep apart.

The problem of three interdependent bodies is not yet completely solvable. We regard two of them as disturbed by the other.

The planets are Mercury, Venus, the Earth. Mars, Jupiter and Saturn and Uranus and Neptune. Uranus was discovered by Herschel, and Neptune was discovered by references to a point obtained by calculation of irregularities in the motion of Uranus.

The asteroids are small planets revolving about the sun in orbits between Mars and Jupiter. Meteors are small bodies also revolving in determined orbits. and at the points where the earth meets orbits of meteors are produced "falling stars," when the meteors burn in the atmosphere of the earth.

Comets move in various orbits. They are sometimes attracted into the solar system by Jupiter, and here they are subject to disintegration, unless some impulse sends them again out of the system. Many comets have a fixed orbit and period; their orbits are very eccentric.

Those which remain in our system are subject to a tidal action so intense that they are broken up and converted into meteors. This is the cause of the "August meteors."

The November meteors are irregularly bunched in their orbit, hence in successive years he number varies.

Professor Searle next touched upon Satellites. The moon rotates on its axis once during each revolution around the Earth, hence keeps the same face always towards the Earth.

Mars has two satellites, the inner of which is remarkable in that it rises in the west, its motion being very rapid. Jupiter has five satellites of which one was discovered last summer by Prof. Barnard of the Lick Observatory. The velocity of light was first determined by observation of the eclipses of the satellites of Jupiter, Uranus has four satellites and Neptune has one which is remarkable as having a retrograde motion.

Prof. Searle postponed consideration of the nebular hypothesis till the next lecture.