The Velocity of Light.

Golden Bay Argus, Volume 4, Issue 35, 25 January 1895, Page 2

The Velocity of Light.

Light moves with the amazing velocity of 185,000 miles a second, a speed a million times as great as that of a rifle bullet. It would make the circuit of the earth’s circumference, at the equator, seven times in one beat of the pendulum. For a long time light was thought to be instantaneous, but it is now known to have a measurable velocity. The discovery was first made by means of tfie eclipses of Jupiter’s satellites. Jupiter, like the earth, casts a shadow, and when his moons pass through it they are eclipsed, just as our moon is eclipsed when passing the earth’s shadow. Jupiter’s shadow far surpasses in magnificence that of the earth. His moona revolve round him much more rapidly than our moon revolves around the earth, and their orbits are nearly in the plane of the planet’s orbit. Consequently they all, vrith the exception of the fourth and most distant satellite, pass through the planet’s shadow, and are eclipsed at every revolution. Roemer, a Danish astronomer, made ir, 1675 some curious observations in regard to the time of the occurrence of these eclipse. When Jupiter is nearest the earth the ajlipseo occur about sixteen minutes earlirr than when he is most distant from the earth, The difference in distance between the two points is about 185,000,000 miles, the diameter of the earth’s orbit, or tvs ice her distance from the sun. It takes light, therefore, aixteen minutes to traverse the diameter of the earth’s orbit, and half that time to span the distance between the sun and the earth. Light is thus shown to travel 185,000 miles in a second, and to take eight minutea—or mere exactly, 500 seconds —in coming from the sun to the earth. It follows that we do not see the sun until eight minutes after sunrise, and that we do see him eight minutes after sunset. When we look at a star we do not see the star as it now is, but the star as it was several years ago. It takes light three years to come to us from the nearest star, and were it suddenly blotted from the sky, we should aee it shining for three years to come There are other methods of finding the velocity of light, but the satellites of Jupitej first revealed its progressive movement.

“ This is a little too late for you to bo out isn’t it, Peok? Aren’t you afraid your wif< will, miss you?” Mr, Prick: “l hopo sin will. She oan fling thing 3 pretty straight though.”