MR. SEVERN'S LECTURES.

Hawke's Bay Herald, Volume XX, Issue 3930, 12 June 1877, Page 2

MR. SEVERN'S LECTURES.

Yesterday afternoon Mr Severn gave a lecture to about two hundred children from the different schools in Napier. The lecture of Saturday evening on the "Earth and its Satellite," was partially repeated with a number of simple experiments, which appeared to give great delight to the young people present. In the evening Mr Severn gave his second lecture, the subject being Spectrum Analysis with experiments. The hall was crowded with a most appreciative audience. Mr Severn began by stating that liis lecture must necessarily be elementary, as he could not go deeply into tlxe question before them. No subject in physics is so overwhelming as that of light. He gave a rapid sketch of the different theories in existence at different periods, with regard to light ; tlxe ancients believing that it was emitted from the eye. Referring to tlxe theory propounded by Newton and accepted by Sir David Brewster and other enxinentmen of his time, known as tlxe emission theory, the lecturer stated that it had been demolished by Dr. Young, who gave to the world what is known as tlxe undulating theory of light. Newton's experiments in refraction were, then explained and illustrated. The nature of a prison and the production of spectrum was explained in a most interesting manner. The lecturer then proceeded with his first experiment — that of sifting a beam of light thrown from the lantern tlxrouglx a small bottle containing bi-sulphate of carbon, and illustrating in a most vivid way the process of refraction. A number of expex-iments were also gone through with the thermo-electric pile and astatic needles. Taking a photograph by aid of the magnesinx light, and then taking one in tlxe dark, were accomplished, tlxe latter experiment showing that light, was present, although not visible to the" eye. In concluding tlxis part of his lecture Mr. Severn referred to tlxe great use the spectroscope had been in the manufacture of steel and in other branches of industry. A number of views of European and colonial scenery were then exhibited, and tlxe lecturer concluded with an exhibition of that wonderful machine tlxe ■■ Radiometer," and an explanation of tlxe cause of motion in the little mill. Tlxe machine was held in the ray of light from tlxe lantern, and tlxe lecturer explained that the heat in tlxe ray repelled tlxe dark side of the arms of the mill, ancl so caused tlxe motion. When held in the red light of tlxe spectrum the mill rotated quickly ; in the yellow light tlxe motion was slower, and ceased altogether in tlxe green and blue lights, showing that it was the heat of the ray which propelled. A most interesting and enjoyable lecture was brought to a close with a display of tlxe working of Six- D. Brewster's kaleidoscope. To-night Mr Severn will lecture upon ** The Sun and Modern Solar discoveries."