ASTRONOMY, PHYSICS, &c.

Otago Witness, Issue 2600, 13 January 1904, Page 29

ASTRONOMY, PHYSICS, &c.

THE IONISATION OF GASES

In this section Professor W. H. Bragg, M.A., of Adelaide, delivered an address on " Some Recent Advances in the Theory of tho lonrsation of Ga^ses." The attendance was largo, the room being crowded with ladies and gentlemen. The President said the ionieation of gases was a subject of great interest, and the interest had recently been increased because by its means the properties of the radioactive substances had been investigated. A gas under the influence of the X-rays or the radiation from radium became ionised ; its molecules were broken into parts, which were negatively and positively charged respectively. Under the influence of electric force these ions could move and constitute a current. The ions appeai-ed to be much larger than the molecules of the gas, and the explanation accepted by physicists was that each ion could be made to become the centre of a cluster of ordinary molecules, which would cling to each other like a swarm of bees to their queen. However produced, the ions had always the same electrical charge, but under different circumstance's the size of the cluster might vary. Occasionally these clusters came into collision -with each other, and the attendant molecules disappeared. The lecturer gave various illustrations of the curious properties of these clusters, ajid showed that it was only when the ion moved slowly that the cluster could bs formed. At high speed the cluster broke up, and the parts of the molecule moved free. Investigations of these quicker moving ions showed that the portions into which the molecule broke were very unequal — one being simply an electron and the other the remainder of the molecule. The president explained the nature of the theory of the formation of new ions by the collision between old ions and ordinary molecules, and showed how the negative ones easily broke oft" the electron from the molecule, whereas the positive ones had to move faster to obtain the same result. It was nece&sary therefore that considerably mere _ electromotive force should be exercised in order that both negatives and positives should become effective ionisers, and when this happened the phenomenon became that of the ordinary electric discharge. Radium itself issued electrons of enormou? speed, able to pierce millions of air molecules without, suffering serious deflection. The Cathode rays, consisting of slower-moving electrons, were more easily deflected and their power of penetration was far less. The president explained some of the recent experimental investigations in this direction, and showed that to an electron whose speed was nearly that of light matter was merely an assemblage of electrons whose grouping into atoms or molecule 3 was immaterial. The subject, the lecturer explained, was a very wide one, and in the course of a brief address he had merely touched upon the fringe of it. At the conclusion of the address Professor Bragg was heartily applauded.