The object of the lecture, as stated by Professor Shand, was more to give an idea of the nature of the evidence which the spectroscope furnishes respecting the existence of common terrestrial metals in the solar atmosphere, than to treat of the whole of so large and interesting a subject. He therefore restricted his attention to a comparatively narrow field of enquiry, connected with solar rather, than with terrestrial chemistry.
He commenced by giving an account of the first step which, was made in the series of discoveries which have led up to the new method of spectral analysis. This was made by Sir Isaac Newton, two hundred years ago. By admitting the sunlight into a darkened room through a small aperture in a window shutter, and placing a triangular glass prism in it, he obtained the rainbow-tinted strip of light to which he gave the name of the solar spectrum. Any strong light would produce the experiment, and for the purpose, the Professor brought two charcoal rods, which were in connection with a galvanic battery, nearly in contact, when a most brilliant and dazzling light was produced. This electric lamp was placed in a lantern, when a ray of light was allowed to fall through a prism in a narrow slit, upon a screen, when the spectrum of the electric light was produced in rainbow colours.
It would be tedious to follow the lecturer in all that was said about the colourations which the various metals impart to flame, the bands or lines peculiar to the spectrum of each metal, the value of the spectrum analysis as a means of chemical research, the number of discoveries made by means of the spectrum, his remarks upon the labours of Kirchhoff, upon refraction, deflection, &c. He exhibited several very interesting experiments, showing the colours given out by various substances, in a Bunsen gas-burner, and their spectrums, by means of the electric light.
He showed that whatever be the nature of the flame in which the salts of a metal are volatised, the coloration, when visible, is always the same for any one metal and for all its compounds. In the last of his experiments, a mixture of the salts of different metals was placed on one of the carbon points, when the hues of the various metals flashed out on the screen, so that each metal was as distinctly recognisable as if the others had been entirely absent.
As regarded the delicacy of this method of chemical analysis, he remarked that it could detect with certainty the presence of one-hundred-millionth part of a grain of strontium or of calcium. Its value as a means of chemical research might be inferred from the fact that already by its aid have been discovered no fewer than four new and extremely rare metallic elements.
In conclusion, he said that those who were desirous of extending their knowledge on this subject could not do better than study the writings of Prof. Roscoe and Mr Proctor. For his own part, if he had succeeded in attracting attention to a new and most interesting branch of scientific investigation, the purpose which he had in view would have been fully attained.