ODD PROPERTIES OF LIGHT.

North Otago Times, 3 September 1910, Page 3 (Supplement)

ODD PROPERTIES OF LIGHT.

WE SEE THE SUN BEFORE IT RISES. Light travels at an enormous rate of speed, some one hundred and eighty-six thousand miles a secoud. But there are some peculiar and teresting arguments based on this. Now, for us to see an object that gives out light, we have to wait until the light wave—as it is termed—reaches our eyes. Of course this is ; not very long in the case of a candle or a lamp; but in the sun's case it takes eight minutes after it has peeped over the horizon for us to see it, because the sun is ninety-two million miles away. In the vast realms of space there arc some suns so far away that their light, though coming towards us at the rate mentioned, has not reached us yet; and there are also some whose light we see and shall continue to see for many years which have gone out. The term of distance in astronomy is a light year, or the distance light would travel in a year going one hundred and eighty-six thousand miles a second. Reflected light travels at the same rate. So the sunlight shining on the earth is reflected off into space, and if the other worlds were inhabited and possessed telescopes powerful enough they could see the same thing transpiring on the earth at different times. Thus, if such a telescope was possible, as there are plenty of heavenly bodies forty-five light years and more from.us, an observer stationed on one of these, instead of seem,,' the events of the election in 1865 when the Liberal party, with Lord Palmerston at its head, was returned, to power, would see them transpiring in all their excitement in 1910! Or if a great mirror was placed on one twenty-two and a half light years away, we should see that election ourselves at the present time reflected from the mirror,

Light travels in straight lines going through only one medium; but when it goes from one to another, as from air into glass, the ray is bent. That is why ws can take two prisms placed properly a nd see round a corner. A very peculiar thing along this line is the bending of the sun's rays on coming from the ether to the air. As air is the denser, the light is bent towards the perpendicular, or down, so that we actually see the sun before it has risen, though it takes eight minutes for its light to get to us. The same phenomenon is observed at sunset. Everyone has noticed in the summer how long it takes the sun to go down when it gets away over in the west. It seems to hang in space quite still, and then suddenly sinks out of sight. When it is hanging thus, it has really already set, and we see it merely on account of its bent or refracted rays. As the suns light is composed of many different colours, and as the red light is .absorbed least, that is why the sun appears red at sunrise and sunset; for. the red is first to get to us and the last to leave. In case we had an atmosphere less dense than the ether to bend the light, then the fastest component of the sun's light would reach us first. This is the violet' rays. Therefore, .at sunrise and sunset the sun would be a violet sun, changing somewhat rapidly through blue and green to its generally observed appearance of brilliant whiteness. Also in this case we should not see the sun until •it had already been above the horizon several minutes.-'Topular Science Sittings."