Want of space has prevented us hitherto from giving s synopsis of Dr. Macgowan's interesting lecture, but we now do so, in the belief that a large proportion of our readers will gain something by its perusal.
Noticing as a preliminary the nature of light, the lecturer remarked that it was formerly supposed to consist of very small particles, but this theory had been abandoned in favour of one which defined it as_a series of undulations in refined ether. He adverted to Newton's ear is of light by means of the prism, but star hat no more discoveries could be made in this direction, because an imperfect aperture, a round hole, was used, which for optical reasons could not give perfect spectrum. Early in the present century Wollaston experimented by a narrow slit, and the spectrum thus shown revealed the existence of numerous dark lines crossing thie spectrum which were long a study among physicists, till, some fifty years ago, a German optician, Fraunhofer, mapped them out to the number of about five hundred, and desi the principal ones by the letters of the alphabet, which are still employed in referring to them. Above two thousand of these lines are discernible by the microscoy The pyrotechine art depends for the m: nificence of its displays on the colors whicl certain metals give elf when reduced to vapor by heat, A further step was made in spec-frum analysis when these colored flames were examined ty the spectroscope.
This instrament took. for its scope the spectrum, hence its designation. When used for microscopic purposes, it consisted merely of a prism attached to a microscope; when for telescopic purposes, several prisms are connected with the spectroscope.
Light from burning metals, it was discovered, threw across the spectrum bands of bright and colored light; each metal having one or more of these, though at the same time each metal had its own place in the spectrum. In this way the presence of any metal could be kuo wa, even in the minutest quantities, by marking the Rrexample, had a yellow band, (shown in the sition that it took in the spectrum. Soda, spectroscope on the table), lithium (also shown) had a pink colored light above the yellow sodium one, and below this might be observed the double bands of cobalt. The extreme delicacy of this mode of detecting the presence of a metal or alkalic was wonderful. "When a chemist by the ordinary means could detect the presence of a thousandth of a grain in mixture, he was considered a good manipulator, but by the spectroscope the 180- tuillionth of a grain of soda could thus be made eS evident to the The lithium here was supposed to exist in only four minerals, but now that the six-millionth of a grain could be detected, it was found that this moral was very widely diffused, in plants, mineral waters, in tea, coffee, and tobacco. As Chinamen saved the hair shaved from their heads for fertilising soils which needed silex, so we might some day husband the ashes of ur pipes for the lithium that the arts might require After the examination of every known substance, some coloured bands wore des cried by Bunsen in the spectrum which had not hitherto been seen. Bunsen had been oxperimenting on the waters from a mineral spring; he evaporated 40 tons, and thus ob-Hned 200 grains of the new metals, Rubium and Caesium. These were found in many mineral waters, the Vichy that some of those present might have been taking being of the number. It might turn out that the healing qualities of these waters were due to the presence of these metals, and that they might be able some day to use them in the form of pill. In this way iodine had supplanted the use of burnt sponge; Dr. Lugal, soon after the discovery that iodine was found in sponge, conjectured that the virtues of the sp. were due to the presence of its iodine, and was right.
The spectroscope also revealed such argante matters as the coloring principles of and vegetables, Blood, for example, exhibited on the spectrum a peculiar line, so that the smallest portion could be detected; guilt might thus be made manifest, doubt dispelled, or innocence established. 'A drop of blood. that had stained a bit of cloth was submitted above twenty years afterwards to the spectroscope, which demonstrated its presence beyond the possibility of a doubt. The spec-
Text read from the printed page and cleaned; old type leaves the occasional error.