THE STARRY SKIES

Taranaki Daily News, 20 July 1935, Page 1 (Supplement)

THE STARRY SKIES

IN PICTURE AND STORY

(By the Rev. B. Dudley, F.R.A.S.) [Written for the Young.] Last Saturday’s article contained a brief account of Sir James Jean’s lectures to the Royal Institution, as published in his recent book, “Through Space and Time.” We now pass on to some details in which we shall see how the author, in his usual striking manner, illustrates the wonders of space in picture and story, so that we cannot fail to comprehend them. i In his chapter on The Earth, Sir James illustrates the meaning of “inertia’* thus:

When, says he, our motor-car is running freely, stopping the engine does not at once stop the car. Not only every object, but every part of an object, seems to want to continue its present motion. If we turn the steering-wheel we can make the lower part of the car follow the front wheels, but the upper part will seem to want to continue on its old course; and if we turn too quickly there is danger of the car overturning. Or if the road is icy or muddy, and the wheels for that reason cannot get a grip on the road, the whole back part of the car will tend to follow its old course, so that the car may skidThat is inertia; and, as Jeans, says, it is a property we often meet with in a study of the heavens. Try to follow him—nay, keep step with him, for it requires no effort to do so—as he explains the circulation of the earth’s atmosphere. The rotating earth drags round with it, but the latter can never quite keep pace with the solid earth which is forcing its motion. “A mountain or other point on the earth’s surface in Norway is moving round the axis of the earth at about 500 miles an hour, while one near the equator is moving at about 1000 miles an hour,” says the author. But, as he further, reminds us, the earth’s power to pull round the mass of air with it is never quite strong enough to speed up the air from 500 to 1000 miles an hour in the course of its southerly journey from Norway to the equator. “The earth’s mountains and surfaces are not rough and spiky enough to get a perfectly firm grip on the air, so that this is always slipping backwards a bit—as a* motor-car does when the clutch is not holding perfectly; and when we feel the air slipping back in this way, we say there is a wind blowing from the east to the west.” Did you ever think of the winds—particularly the trade winds—in this way? The sun and the moon are so bright that most people think of them as larger than they really are on the background of the sky. Jeans helps the imagination in his own picturesque way. “The whole sun or moon, moves past any fixed point in two minutes; and this shows that it would ' take 720 suns or moons placed in contact side by side to make a circle round the sky. From this we can calculate that if we had to wallpaper the whole sky with suns and moons, we should need about 200,000 of either.” This false estimate of size causes Jeans to remember that most people who have never before thought of it, on being asked how many threepenny pieces they can lay' on a halfcrown without overlapping them, declares the number to be at least two, whereas an actual experiment shows that not more than one can be so placed. This illustrates the value of experiment. Since the Moon is a much smaller body than the Earth and therefore lighter —a feebler magnet, let us call it—a person like ourselves could leap to enormous heights on arriving there. It ought not to be difficult to break one’s own jumping records or even everybody else’s. “A good jumper ought to jump about 36 feet, and the long jump of a fairly good athlete ought to be at least 120 feet.” If, says Jeans, ,we decide to play cricket, “the ball will simply soar off our bat, so that it is not to be entirely a batsman’s game, the pitch and field must each be six times the size they are oh earth.” But, as he reminds us, there are certain disadvantages. For one thing,- "all this will make the game six times as slow as on earth,” and perhaps cricket played six times as slowly, he rightly thinks, would be rather tame sport. Again, there would be no encouragement to set up big guns on the moon, because if shot were sent up from such machines as were used in the Great War, the shot would never* come back. “Their projectiles would go right off into space and never return.” As a matter of fact, we “could produce the same effect as earth’s war-guns achieved with something much simpler—a breath of air from our breathing apparatus.” Unfortunately for this, however, there is no air on the moon—nothing to breathe—and therefore when we arrive on the moon we shall not be able to try the experiment. In truth, this is why there is no lunar atmosphere: the moon is so weak in.its gravitational pull that it would be quite unable to hold an atmosphere, if it were suddenly, by some miracle, wrapped round with one. Each molecule of air, being so light, would jump clear off into space. We must even take water with us when we go to the moon, the author warns us. Nor will it do to pour it out and leave it standing; “if we do,” he says, “it will have disappeared by the time we want

to drink it—its molecules will have danced off, one by one, into space.” He does not therefore recommend the experiment, and advises *us against picnicking in Moonland. Jeans describes the heat which the different planets receive from the sun, the amount varying greatly according to their distances from the central fire. This glowing body “pours out heat and light in all directions like a fire,” he says; “the planets are like a number of sentries walking round and round the fire. The nearest man may be uncomfortably hot, while the farthest may be uncomfortably cold, unless he has private supplies of heat to keep him warm independently of the warmth he receives from the fire.” The earth and some of.the other planets have private heat of their own; but if is. very little. ■They derive their warmth almost entirely from the sun’s radiation. When comparing the planets with, each other, Jeans says that if Venus is a twin sister of the Earth, Mars is the Earth's little brother: if Venus is a warmer edition of the Earth, Mars is a much colder edition; and if Venus suggests a picture of what the Earth may have , been in the remote past, then Mars suggests what the Earth may possibly be in the remote future.