LECTURE ON THE SPECTROSCOPE

New Zealand Mail, Issue 1511, 14 February 1901, Page 16

LECTURE ON THE SPECTROSCOPE

A lecture was given by Mr J. W. Poynton on the 6th in the New Century Hall on “ The Spectroscope and Its Uses.’’ There was a good attendance. By the aid of diagrams the lecturer explained the principle of the instrument. There was, he said, an analogy between sound and light. H'gh musical notes were due to air waves rapidly succeeding each other at regular intervals, lower notes by similar waves of lesser frequency. Light is conveyed from the sun solely by the trembLing of the ether. It' has a rate of motion, as sound has, but vastly greater. Different colours are caused by different wave lengths; rose colours being due to longer waves than the blue, just as the treble and base notes in music are produced. * When a beam of light falls on a bed of flowers of different colours these waves are sifted out from white light, which is composed of waves of ail lengths mixed together. Some waves are absorbed, others are rejected by the petals, and, falling on our eyes, give us the sensation of colour, a.s air waves give tss the sensation of sound. These waves can be separated by passing a beam of light through a wedge-shaped piece of glass. The shore or blue waves are bent more towards the thick end of the wedge than the longer, or red waves, and so the beam is spread out like a fan. If it is thrown on to a screen it will be a streak, red at one end and blue at the other, with other colours between. So sensitive was a test described by the lecturer that with fine instruments the 200,000,000 th part of a grain of sodium salt could be detected. A number of instances of the delicacy of this test were given. A very accurate test for blood, no matter how old the stain, is thus afforded. The bright lines given by a substance when heated are replaced by dark ones if a beam of light be sent through the vapour of the substance. For instance, mercury gives a system of bright lines when heated; but if a beam from a lamp be .sent through vapour dark lines appear at these places. This is important in determining constituents of the sun, which is mainly a mass of highly-heated vapours. Iron, carbon, hydrogen, phosphorus and many substances known to uis were detected as vapour in the sun, because, no matter how far away the source of light, this method cf analysis could be applied. The spectroscope also shows that many of the stars are moving towards or away from us. The lecturer proved this by a happily-worded illustration. By watching certain double lines he described, and noting the amount of displacement for each, the time they take to complete their journeys up and down the streaks (which may be hours, days, weeks or years) may be determined, as well as the comparative size of these colossal bodies, the distance from each other, and the time taken to complete their revolution asound each other, although they are so remote that the most powerful telescope shows them only as single stars. In some cases there are three or more systems of moving lines, perhaps two huge suns i evolving around each other, and, far out in. space, another revolving around these two, and completing its mighty orbit at intervals of perhaps centuries. The lecturer gave other instances of the use of the spectroscope, and claimed that the discoveries made by this beautiful instrument stood high among the triumphs of the century just closed.