HUMAN ENDEAVOUR

Evening Post, Volume CVIII, Issue 148, 19 December 1929, Page 30

HUMAN ENDEAVOUR

COMPARISONS OF SPEED

'PLANES/BULLETS, STARS,

AND ATOMS

I The speeds attained in the wonderful performances of Flying-Officers Waghorn and Ateherley in the race for the Schneider Trophy invite a comparison with speeds familiar in other departments of human endeavour and scientific) inquiry (writes W. M. Smart, | M.A., D.Sc, F.R.A.S., in the "Observer"). In round figures the winner of the trophy flew his Supermarine Rolls-Royce S-6 at a speed of 330 miles per hour, or five and a half miles per minute, or about 160 yards per" second. In a second he covered just twice the distance between two consecutive telegraph poles by the roadside. - The immense muzzle velocities of the biggest guns naturally come to mind at once in a comparison of this kind and sa an example the performance of Big Bertha," which bombarded Paris from behind the Gorman lines in the latter part of the war, may be cited. The velocity with which this weapon discharged its projectiles was roughly six or sevea times the speed of Wa<*horn's seaplane.' The physicist in'his laboratory would probably claim that he deals with the highest speeds of all. For example, he can bombard a screen with "alpha particles" (the nuclei or cores of the helium atoms) travelling with speeds of many thousand miles per second. The physicist, however, is not very much interested in what the actual speed of his microscopic and invisible particles may be ; his.main concern is with the information which the shattering impact of the high -velocity projectiles on complicated atomic structures enables him to acquire. EARTH SPEEDS. The astronomer, on the other hand, regards the study of the velocities of the stars as of the utmost importance in his efforts to comprehend the structure and the evolutionary history of the universe. Before referring to stellar velocities, some other speeds of astronomical interest may be mentioned. _ As the earth Bpins or rotates about its axis a point on the Equator is whirled round with the speed of about 000 yards per second. A reader of the Observer" sitting quietly in his chair ie London has a speed due to the earth's rotation of about 320 yards per second. But he is' not conscious of anything uncommon in this respect, for all the objects in his immediate vicinity are also being whirled round at a speed of 320 yards per second. Two trains approaching a station on parallel lines afford a familiar analogy, A traveller in one train, fixing his attention on the opposite carriage of the second train, en3oys the sensation of rest, which is, of course, dispelled immediately when his gaze is transferred to the usual objects that form the "fixed" scenery of a railway environment. Again, the earth in the course of a year journeys round the sun in a nearly circular path measuring about 580 million miles, A simple calculation shows that the earth's orbital velocity is close on 19 miles per second. Meteors or "shooting stars" provide' another illustration of the immense speeds common in astronomy. The meteor itself may be no larger than a grais of sand, but owing to the. great speed (20 miles per seeoni. or more) with-which it enters the atmosphere, it m -ilatihsed and rendered luminous-ci-nt. for a brief but glorious instant by the frictional resistance of the air. STAR'S 93-MILES A SECOND. The speed of a star across the line of sight is deduced from two distinct measurements. The first is the measurement of the change in direction over a long interval of time, and the second is the measurement of the star's distance. The spectator of the Schneider Trophy race had the convenience oi_ fixed distant landmarks against which to estimate, if he wished, the rate at which a seaplane's direction changed, say, in an interval of five seconds. Similarly, the astronomer measures the rate at which a star's direction is altering as viewed against the background of faint stars, which, beine' presumed to be very much more dis- ! tant than the particular star under con-' sideration, form a pattern of nearly ! fixed reference points. But, except for i a few hundreds of rapidly moving '■ stars, he has to wait for perhaps ten : or twenty or fifty years before the ! mmute changes in direction can be ac-' eurately measured. The star with the greatest proper motion (as the rate of "i change of direction is called) moves \ over ten seconds of arc per annum. If the reader imagines a halfpenny situated at a distance of 600 yards from him, the difference in direction of the opposite ends of the diameter of the coin is just ten seconds of arc. This particular star (Barnard's Star, as it is called) is one of our nearest celestial neighbours; its distance is known with high accuracy to be six light-years or -about 35 million million miles. A simple_ calculation then gives the speed at which it is moving across the line of sight; it is 56 miles per second. The speed at which a star is increasing or decreasing its distance from us (the radial, velocity) is' measured by spectroscopic methods. Barnard's Star is _ approaching us with a speed of 74 miles per. second, and its velocity m space relative to the solar system is 93 miles per second. THE SUN. The sun is a star, and, like every other star, is dashing through space accompanied by the earth and the other planets with a speed compared with which terrestrial speeds are almost insignificant. Relative to several thousands of the nearest stars, the sun is travelling with a speed of 12 miles per second in a direction near to that in which the bright star Vega is seen. (Vega is nearly overhead about 8 p.m. to-night.) ■ ■ The greatest radial velocity measured is that of a faint nebula in the constellation Coma Berenices; the value (measured spectroscopically just two or three months ago) is nearly 5000 miles per second away from the solar system. But the doctrine of relativity is against ascribing the interpretation of such measures as entirely due to a velocity effect, but rather due to the effect of distance. It is noteworthy that a group of nebulae associated in this part of the sky has recently been found to be at the stupendous distance of 50 million light-years—the greatest distance yet measured in astronomy.