SOURCES OF LIGHT.

Auckland Star, Volume XXXVII, Issue 197, 18 August 1906, Page 6

SOURCES OF LIGHT.

i ■ ■■ LECTURE BY PROFESSOR BROWN. That the faculty of communicating scientific facts in an interesting manner , is possessed in a marked degree by Professor F. D. Brown, M.A., B.Sc., F.C.S., was demonstrated at the Leys Institute lost night, when that gentleman explained the sources of light. As usual, when Professor Brown is announced to deliver , a lecture, there was a large attendance, and from first to last the interest of the audience was plainly manifested, the various interesting experiment, illustrative , of the subject being watched most attentively. Mr. T. W. Leys presided, and eaid it was hardly necessary to introduce Professor Brown, as that gentleman had delivered the first lecture given in the institute, and had ever siiwe shown great interest in its success. 'He must say lie felt some hesitation in asking Professor Brown to lecture, as it involved an enormous amount of trouble to that gentleman, as could be seen by the apparatus on the platform. Professor Brown was received with applause upon rising to address the meeting. He first of all pointed to a lighted candle, and asked, "Why docs that give light, while this bunscn burner and hydrogen gas flame do not?" Professor Brown then held a plate over the bnnsen burner and also over the hydrogen gas flame to show that it did not become discoloured. Next he held it over the candle, and over an ordinary go's jet, and showed the audience the deposit of soot resulting. "That proves," said the lecturer, "that flames which give no light, produce neither smoke nor soot, while on the other baud, the flames which give light also produce soot. Therefore it would naturally appear that the light must be due to the presence of atoms or particles of carbon in the candle and the ordinary gas jet. A lamp with turpentine in it was next lit, with the result that there was both a light, and also heavy smoke. By conveying this smoke to the bunsen burner, the lecturer demonstrated that it caused the ilame from the burner to at once become luminous, which he pointed out wns probably due to the carbon parti- I elea being heated to a high temperature. ] Professor Brown next held up a glass vessel filled with chlorine gas, and ex-1 plained that one peculiarity of that gas was that it combined very readily in- ' deed with hydrogen. A piece of paper saturated with turpentine was then dropped intr/ the vessel filled with chlorine gap-,' with the result that an explosion took place instantly. Professor Brown .hen held up the glass vessel, and pointed out that ihe result was a deposit of soot. A spirit lamp was then lit. and the attention of the audience drawn to the fact that the flame from tUe alcohol was not. luminous; chlorine. gas was then added to the flame., with the result that it. readily took up the hydrogen, and leaving the carbon ihe light became luminous. Several highly interesting experiments followed to further demonstrate this fact, and to explain that the luminous part' of the flame, from the ordinary gas burner was from the gas. with the faculty of the least rapid diffusion, which formed a core. of heavier gas. Having

explained the composition of the flame. Professor Brown next demonstrated by experiments that luminosity was due to carbon particles at a white heat. He said when that fact was understood many systems were tried to heat the gas, "as in the case, of what were called regenerative burners. Finally it was decided that the only way of getting I light satisfactorily was by abandoning the idea of applying carbon particles. I and putting sonic other substance into I the flame which when it got to a white j heat would suit, the purpose of assuring luminosity. "Thirty years ago," said Profcsor Brown, "1 discussed with a professor at Home the idea of platinum gauze being used for that purpose. That was long before the incandescent mantle was discovered." Professor Brown then held platinum wire in the flame of the bunsen burner to demonstrate how readily it became incandescent. He explained, however, that platinum being dearer than gold, was a bar to it being used for that purpose. Next, taking up a piece of black silk net, he burned the material in the flame from the jet. and pointed out that there remained, what he termed, "a sort of ghost of the material." (Laughter.) This was then held in the flame from the bunsen burner, and at once heeanif incandesccni. Having led his audience by simple stages up to this point, the lecturer then referred to the discovery by Welsbach, of Austria, of the incandescent mantle, which, be explained, was simply woven cotton saturated iv thorium nitrate. "It is not unlike a stocking," remarked the lecturer as he held up a sample, then he pressed it over a mould to make it into the shape of the ordinary mantle, and having burned out the cotton, hung the remainder over the flame from the bunsen burner, when a brilliant light was tbe result. Professor Brown next gave some interesting illustrations of how the respective illuminating powers of different lights were ascertained by measurement. A very simple process was through shadows "on a screen from a candle and gas light. When the respective shadows thrown were equal, by measuring the nearness of the candle to the screen, and the further distance off of the gas light, the actual illuminating power of each was readily ascertained. A still more, interesting experiment, however, was shown to illustrate ti.e respective value of the Argand and the Welsbach lights. Two blocks of paraflin were put side by side with only tinfoil between them. One light was put at each side and in front was a black board, so that only the blocks of puraltin could be seen through an opening. The Argand light showed the paraffin a brownish colour, while the We&=ba_:h was greenish, When the lights had been so arranged as to show about equal power in the respective blocks of paraffin, measurement, as before, from each light to the object illuminated, demonstrated the great, superiority of one over the other. Without going into detail regarding the electric- light, Professor Brown gave a most interesting experiment illustrative of Nicholas Tesla's "high frequency fields" system. A numljer of glass tubes were arranged one above the other on a wooden stand. An electric apparatus was then sot in motion, whereupon each tube diffused a bluish light. Professor Brown explained that the tubes were vacuum ones, tftte air having been pumped out. He pointed out that they were in no way connected with each other, and to demonstrate the existence of the "high frequency field" lifted two of the tubes, aud moving them round the others, they still had the light in them so long as'he did not go beyond a certain radius. "It may be possible/ said Professor Brown, '-'that this will be the light of a future generation, for if one had walls of glass under, similar conditions, the light might be produced in the same way throughout the walls and after all you know cheapest light is that of the glowworm which this much resembles." The lecturer, however, did not anticipate that this form of lighting would be speedily adqited for OTdnjary

So deeply-interested were many of the audience in the lecture that Professor Brown remained for some time after the meeting had ended, explaining various points, and repeating some of the , experiments. At the invitation of the chairman, Professor Brown was given a most hearty round of applause at the close of the lecture.