MYSTERY OF LIGHT.

Grey River Argus, 26 November 1928, Page 3

MYSTERY OF LIGHT.

WONDERS OF UNIVERSE / •*» — ' - - -,. «_?=r jr-e-j fc-» -nv rr BASIS OF AR MT SOUND KA XU ING In his presidl't'Htal address to. the British Association, Glasgow, Sir William, Bragg dwelt upon the ini mensity of the undiscovered realms of modern science. 1 Nothing in’the progress of scienc*' and more particularly mpfiem science said (Sir William, “is so impressive as the growing appreciation of the immensity «of what a Waits discovery, and th' » contrasted feebleness of our ability to put into wt.rds even so much as we already dimly apprehend. “There is a problem of which the minds of physicists have been full iu ree nt. years. The nineteenth century theory of radiation asks us to look on light as a series (if waves in an al'.pervading ether. The theory has been marvelloiisly succcYsfnl, and the great advances (*f the ninett euth centurv physics were largel based upon it. “In the last twenty or thirty years a vast new fi( 1.1 of optical research «as been opened up, and among the ■‘urious things w i have found is tlu fact that? light has the properties of i. stream very minute A S‘range Problem “A wave theory is of no use in the new field. How arc T.»e two views to be r conciled? How can anything at once be a wave and a paVticiq? I do not. believo that T am unjust to any existing thinker if I say that no one y< t has bridged the gap. “It may be a step forward to say, ns we havU been saying vaguely for some years, that bo<th| theories are true," that there are corpuscles and there are waves, and that the former nr I actually "responsible for the transference of energy in light and heat, and for making us see; while the latter guides the former on their way. “We are hers face to face with a

strange problem. We know that there must J»e a reconcilement of uur contradictory experiments; it is surely cur conceptions of tl.* truth which ar° at fault, though cadi conception seev valid and proved There must be a truth which is greater than any <.f v>ur descriptions of it. “Here is the actual ease where the human mind is brought face to’ face with its own defects. What can we do? As physicists we can u<e either hypothesis according to the range of experiences that we wish tn consider. To repeat a phrase which I employed a few days ago in addressing a University audience familiar with lecture time tables, on Mondays Wednesdays and Fridays we adopt the hypothesis on Tuesdays, Thursdays and Saturdays the other. (Laughter.) “Wc know that we cannot hp seeing clearly and fully in cither case, but we are perfectly content to work and wait for the complete understanding.” AN INTERESTING EXPERIENCE Sir William illustrated his meaning by an interesting experience du ing the Great War. A number of young scientific students from the universities, he said, was assemb’ed for t ie purpose fo testing on the battlefie’ds the value of guns as were already known. <r Tn their mutual discussions and considerations it became clear to them that the great desideratum was a method of measuring very exactly the time of arrival of the air pulse, due to the discharge of the gun. at various stations in their own lines. If the .dative positions of the stations wore accurately known it would then become a matter of calculation to find the gur position. But the pulse was very feeble; how could it be registered* *‘Various methods were considered, ami among them was on which no doubt seemed far-fetched and unlikely to be successful. A fine wire is made to carry and electric-current by which it is heated. If it is chilled. for example, by a puff of cold air, the re sistance t 0 the passage of the currem increases, and this is an effect whict ean be measured if it is large enough

It, then, the hot wire couLL.T*e made to register the arrival of th/ air pulse from the gun a solution of the problem was in hand. • *ait of an Aeroplane. “But could the faint impulse from a gun miles away produce an obvious .hill in a hot wire? On first thoughts it did not seem likely and the suggestion lay in abeyance. But it happened that one summer morning an enemy aeroplane came ever at daybreak on a patrolling expedition. An officer lay awake in his bnuk listening to the discharges of the anti-aircraft guns and the more distant explosions of their shells, “Every now and then a faint whistling sound seemed to be connected with the louder sounds. The walls of the hut were of felt; it was in poor condition and there were tiny rents close to his head as he lay. The gun prises made a feeble sound as they cam, through. This set the officer thinking: if rhe pulse was strong enough to make a sound -it might be strong enough to ehill a hot wire perceptibly. “Soihe method was proposed to the company as worth trying. It was tried. It prosed to be a complete success and the sound ranging of the British Armies was based upon it ”