MYSTERY OF LIGHT.

Gisborne Times, Volume LXVIII, Issue 10753, 26 November 1928, Page 7

MYSTERY OF LIGHT.

THEORIES AND SURMISES; >. WONDERS OF UNIVERSE, • BASIS OF ARMY SOUND- \ RANGING. ;Y> • • 'LONDON, Oct. 5. In his presidential address to tfio British Association,, -JSir .1 William Bragg, dwelt’Upoff' the immensity of the undiscovered in the realms: r or modern science. c' .. “Nothing in the ..progress, or • science,” said Sir -William, ‘‘is so impressive as the growing appreciation of the immensity of what awaits discoyery, and the Contrasted feebleness of our ability to put 'into word* even so much as we already dimly apprehend. g * “There is . a problem of which‘ tno minds of physicists have. been fully in recent years. The nineteenth century theory of radiation asks us. to look on light as a series of waves in an all-pervading etljer. The theory has been marvellously successful, find * the great advances of nineteenth century physics were largely based upon it. “Inrthe last twenty or thiry years a vast new field of optical research has been opened up, and among the curious things we havie found is the fact that light has the properties; of a stream of very minute particles. A STRANGE PROBLEM.

“A wave theory, is of no use in the over field. How are the two views to be reconciled l'How can anything be at once a wave and a particle?'l do not believe that I am unjust to any existing thinker if I say tint no one yet has bridged the gap. It may be a step forward to say, as we have been saying vaguely fort some years, that both tneories are true, that there are (corpuscles and there are waves, and ''that'.•■the for- - mer are actually responsible for the transference of energy in light and heat, and for making us rce; while the latter guide the former on theirway. ’• •. ? • • , “We are here face to face wAn a strange ruioblem. We know that there must be a reconcilement of our contradictory experiments ; it is surely our conceptions of the truth which are at fault, though'each conceptionseems valid and proved. There must be a truthjyhich is greater than aav. or our descriptions of it. “There is the actual case v here • the human mind is brought face toi face with its own defects. What canwe do? As physicists we r-se either • hypothesis according to'the range of experiences that "we wish to consider. To repeat a phrase which I on ployed a few days ago in addressing- & uni- ■ versitv audience familiar • ith lecture time-tables, on -Mondays, Wfdnes--davs and Fridays we adopt the one' hypothesis, on Tuesdays, Thursdays, and Saturdays the other (Laughter.) “ We know that we cannot be seeing clearly and fully in either case, '- but are perfectly content to work * and wait for the complete understanding.”

AN INTERESTING EXPERIENCE.

Sir William, illustrated his meaning bv an interesting experience during the Great War. -A number- ofyoung scientific .students from the' universities, he said, was assembled for the purpose of testing on the : battlefield the value of such methods of locating enemy guns as were already known. “in 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 relative positions of the stations were actuallv known it- would then become a matter of calculation to find the gun position. But the pulse was very feeble; how could it be registered? ; - - “Various methods were considered and among them was one which, no doubt seemed far-fetched and unlikely to be successful. A. fine wire is made to carry an electric current- by-' which it is heated. If it is chiilod* for example, by a puff of-cold air, the resistance to ‘the passage of -th*‘ passage of the current increases, and this is am effect which can be- mea- • sured if it is large enough. . If. then, the hot wire eou!d v .b§vmaile to. register the arrival of The air pulse from the gun a solution of the problem was in hand. VISIT OF AN AEROPLANE.' “But could the faint impulse from a o-un miles away produce an obvious chill in a hot wire? On first thoughts it did not seem likely and the suggestion lay In abeyance. “But it happened that one summer niorning an enemy aeroplane cam-6 over at daybreak -on a .pa.trolling expedition. An officer lay awake in- his bunk listening to the discharges of the anti-aircraft gun s and'the more distant explosions of their shells. ’ . . - . “Every how and then a taint whistling sound, seemed, to be connected with the louder sounds?. The wall of the hut. was of felt; ' it- was in poor condition and there were tiny rents close to liis head as he 1ay...The gun pulses made _ a sound as they came through. This set the officer“ thinking ; if the pulse , was stroiig enough 'to make a sound it . might be strong enough to chill a hot wire perceptibly. , - “So the method was proposed to the company as worth trying. It was tried. It proved to be a complete success and the sound ranging of the British Armies was- based upon it.”