Lecture by Professor Searle.

Last evening in Sever 11 Professor Searle delivered a very interesting lecture, his subject being, "The Earth."

Professor Searle said that Astronomy is that branch of Physics and Chemistry which treats of objects beyond the earth. It is dependent on mathematics, for Astronomy and Geometry are allied. If popular instruction were given in Astronomy only recitations of opinions could be given, thus making the teaching difficult, because practical experiments must be made and this is not an easy thing to do.

We depend on the eyes for all knowledge of Astronomy and we must therefore understand of what our eyes are capable It is a curious fact in vision that we cannot be sure that we tell that which we see, because our reason takes part in what we observe. In order to find the points of the compass we must first find a level surface and then by the arrangement of angles we must find the zenith of the sky. A single point however does not help us, and another must be obtained. Looking to the north we can find stars forming circles, and as we go farther north we find the circles growing gradually smaller, till at last they seem almost to stand still. We arrive at the north star but this is not at the pole, for by means of the helioscope one may see many stars nearer to the pole. Farthest north the circles appear to be concentric. We now have the pole and the zenith, and the points of the compass may be determined. In order to find the south pole, the preceding operation is of course carried out in the opposite direction.

Suppose now that we take east and west as half way between north and south, then the equator passes through the two former points. In speaking of the east and west one may mean of the sky or earth, which is inaccurate. So in connection with the stars we should speak of the east as the "preceding" direction and the west as the "following."

The ancient astronomers came to the general idea of the spherical shape of the earth for they observed that as one travelled north or south he found that the position of the pole in regard to the position of the zenith changed. If one travelled south, the pole became farther distant from the zenith, and if north, it became nearer. This then took place either because the earth was round or the pole was an object so near that it might be passed and left behind. But the ancients observed that the stars were very far distant and therefore arrived at the conclusion that the earth must be round.

They noticed also, in travelling, the change of the angles between the zenith and pole, and by measuring the distance travelled and the change of the angles they were enabled approximately to measure the circumference of the earth.

If the position of the pole were observed for many years, and records taken, we should see that its position is not always the same. For instance the star Vega will in 12,000 years be called the north star.

The travelling motion of the earth is due to the earth's shape which is not exactly round, but spheroidical. There is also another motion which is the motion of the axis of rotation which has to do with latitudes. By expeditions sent to different parts of the earth, it was determined that when the pole left one latitude it went in an exactly opposite direction, which proves that the latitudes of places change.