MR. SEVERN’S LECTURE.

New Zealand Times, Volume XXXII, Issue 4982, 12 March 1877, Page 2

MR. SEVERN’S LECTURE.

LIGHT AND SPECTRUM ANALYSIS. To say that Mr. Severn’s lecture of Saturday night was in every respect a remarkable success, would be the least that could be said of it. His Excellency the Governor was present, and the hall was crowded with a most attentive audience, amongst whom we noticed a large number of our leading citizens. The earnestness arid determination with which Mr. Severn takes hold of his subject, the skilful manner in which he manipulates his experiments, and the successful' way in whish he carried hi* hearers along with him, as he did for more than two hours on Saturday evening, is the best possible proof that the subject though difficult was treated in a masterly manner. As these lectures are delivered viva vo:t> and the room darkened to admit - of the experiment with light being seen, it is no easy matte* to give our readers a proper resume of .the lecture. The subject of light was first explained according to Newton’s theory that a luminous - body sent forth particles of light; these striking the eye, became visible. Then Young’s undulatory theory was explained and comparisons made between it and the ripples of water and vibrations of the air when transmitting sound. All these matters were explained in an excellent manner. Refraction was next explained, then the wonderful prism. The Browning’s lantern for experimental work was now brought into use, and the room wholly darkened. A ray or beam of light was shot out from the slit nozzel of the apparatus, and brought to focus by means of a large condensing lense., On the screen as image or band of light in an upright position was seen—this was shown to be simply the image of the opening through which the light was being sent. Mr. Severn caused some very dense fumes to rise and collect about vaiioun portions of this beam of - light with a view to render it 'visible.- This was most interesting. Nest a block of glass with parallel sides' was placed in, front of the opening. The lights falling perpendicularly on this, did not-alter the baud of light on the screen ; but when the block was placed obliquely, the band of light was moved to one side. This was caused the power that transparent media have of bending a beam of light; it is, in fact, refraction. The next series of experiments wen of

extraordinary interest ; the beam, or ray, wathrown on to n reflector; the focus of this was brought to bear on a piece of phosphorus, which at once caught fire ; the beam or ray of light was thus proved to contain heat as well as light. The heat was next taken or sifted out of this self-same ray by passing it through a chemical solution and although there appeared to be the same quantity of light as before, there was no heat, the phosphorus refused to burn. Next the ray was sent through a solution of iodine, ana m this case there was no visible light on the reflector. All seemed dark, and yet the heat proved to be there, for the phosphorus was at once ignited. During the execution of these beautiful experiments and at the close of each rounds of applause greeted the lecturer, who continued to scale the ladder of light yet higher for t- e next experiments were with the prisms themselves. A ray was darted through one of the angular blocks of glass, and it was at once bent aside, and gave the audience the first view of the spectrum. Mr. Severn explained Newton’s experiments—the dispersion or opening out of the beam of light, the cause of the colors of the spectrum being in reality due to the fact that white light, or daylight, was really composed of those colors; if it were not, daylight would not be white light. The cause of color was made plain, and then the analogy between sound, heat, light, and chemical action was placed before the audience in a manner that could not be misunderstood. The spectrum by one prism was now recomposed into white light by means of a second prism, and here the led urer fairly challenged his hearers into adnutting the truth of white light being composed of all the colors of thespectrum; then two pri-ms were applied, and a magnificent spectrum some 10ft. in length was produced on the screen. The portions of the spectrum containing beat, light, and chemical action were now again brought under notice, and ultimately a photograph was taken in the violet end of the rays to prove the existence of chemical action, or invisible light. The photograph was thrown on to the screen amidst great applause. Ihe radiometer invented by Air. Crookes was next exhibited and explained, very much to the wonderment of the audience. After over two hours lecturing, Mr. Severn stated that owing to gome fault in the gas supply to the hall, he would have to postpone any further experiments till Monday evening. Having thanked his Excellency for hia presence (who, we understand, expressed himself as very much interested) and the large audience for their kind attention and patience, the meeting soon dispersed. We cannot speak too highly of such gatherings as these, as they must promote scientific taste amongst the people.