SCIENTIFIC MARVELS

Otago Daily Times, Issue 17974, 29 June 1920, Page 6

SCIENTIFIC MARVELS

DR JACK'S POPULAR LECTURES. ! ABOUT EliliOritO'Nii AND X RAI'S. Profossor 0(u;k continued hits eeiiea of popular (scientific lectures to another largo audience in the physics lecturo room last night. He began by explaining something of the nature of electricity and of the naturo of the atom. Tlio removal of oloctrone from the adding of them to atoms gave rise to negative cur positive ohargca of electricity. The first way in which electrons ooiild bo removed ot added was by friction, as in the case of mercury Bhaken in a tube or the rubbing of silk on glass. Tlio latter experiment made electrons go on to the silk. Tho glass was robbed of electrons, and! thorcfore had an excess of positive electricity left, tho effects of which could be clearly seen in its magnetic properties. If vulcanite was rubbed on catskin it was the vulcanite that took tho extra number of electrons. Although wo saw nothing there was really a strain in the ether, between two charged bodies. In lightning there wag one cloud with a lot of positive electricity on it and another cloud with a lot of negative electricity on it. Tho air between was pervaded with ether, and when that other broke down there was a flash of lightning. Electrons colliding with atoms also struck other electrons off. The heating of a wire drove electrons out from it, iand that fact was now specially used in connection with X rays and radio-telegraphy. Electrons were also driven out by the action of other rays such as the ultra-violet rays. He showed that tho flow of electricity was like the flow of water with wires in place of pipes. The action of tho induction coil or a dynamo in making tho electric pressure was analogous to the action of a pump in raising water. He illustrated the changes that took plaoe in a glass vacuum chamber as the air was gradually withdrawn until tho "broches' dark spaoe" filled the whole bulb and then the cathode rays (electrons really) were formed by the striking of electrons travelling at great speed against the sides of the glass. By further experiments Dr Jack showed that the cathode rays were negative, that they produced phosphorescence, and that they moved with the great velocity of about one-tenth the speed of light. This velocity depended upon the amount of exhaustion and on tho amount of olectrical pressure. 'When the cathode rays struck on a solid X rays were produced. For some kinds of treatment very penetrating X nays of very 6hort wave length wers lequired, but for the treatment of skin diseases they did not require to be so short. Ho proceeded to explain how X rays were derived from cathode rays, and described the revolution in wireless telegraphy caused by Cooliuge's discovery of the hot cathode ray 3 produced from an electrically-heated wire. He illustrated by experiment the properties of X rays in producing phosphorescence and in making solid objects transparent. These X rays were the same in nature as light waves. In mica we had the thin sheets required testing the wavo lengths of X rays, and an X ray spcctrometor could bo made for measuring the X ray wave lengths. By this it could ha ascertained how the atoms I in different substances were distributed. The X rays had power of acting on photographio plates, and so photographs oould be taken witih their aid. This fact was used for medical purposes, and for the detection of flaws m metals or wood. A number of improve- j mont/3 wore still needed! in connection with X rays. In America a portable type of X ray bulb was being produced by means of which a doctor could take something like a Kodak photo of his patient. As the means of producing X rays were improved the uses of them would be greatly extended. Passing on to the subject of the discovery of wireless telegraphy and telephony, JJr Jack said that Clark Maxwell had showed about 50. years ago that light was an electromagnetic disturbance. In 1887 Maxwell's discoveries were first used by Hertz to make electric waves experimentally. The next big step was ink on in 189G by Marconi, who was then only about 21 years of age. The development of the latest electrode valve was cCue not to any ono man but to a group of men each contributing something.- The whole application of these discoveries to wireless telegraphy dated back no further than the beginning of the war. He proceeded to illustrate the production of stationary electric waves along wires, and Hertz's experiment making waves go out in wireless telegraphy. In conclusion, he announced that the next lecture would be devoted to a. further discussion of wireless telephony and telegraphy.