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Spectrum Analysis: Spectroscope
It may easily be imagined that a delicate instrument, such as the spectroscope, might soon suffer in rough hands, and in the dust and grit inseparable from iron works. The Bessemer Spectroscope is therefore well protected by a mahogany case, the slit being covered with glass. The cut on preceding page will show the appearance of the instrument. The observer stands with his back to the bright flame from the metal, so that his whole attention may be concentrated upon the spectrum. This he views through the telescope which is seen issuing from the top of the case.
A still more wonderful result of the discovery of the properties of the prism is seen in the foundation of two new branches of science, namely, stellar and solar chemistry.
The fixed stars are so remote from this earth, that we can form no conception of the vast distance which separates them from us. Light travels at the enormous rate of 190,000 miles per second. Yet the light of some of these stars would take two or three hundred years to travel to this earth. Astronomers tell us that the light of some of these may have been quenched hundreds of years ago, but the fact of their extinction is not yet evident to us. In the same way new stars may during the same period have come into being, but their light has not yet reached us.
The light from these remote bodies has been analysed by the Spectroscope, and remote though they be we are enabled to recognize in their spectra, elements familiar to us upon this earth. These marvellous secrets of nature are not unfolded by any very elaborate description of instrument, but by a little spectroscope that could almost be carried in the waistcoat pocket. I allude to M'Clean's star spectroscope, which is figured above. I need hardly say that when in use, this instrument is used in conjunction with a telescope. The spectroscope has given us a knowledge of the sun and its surroundings such as we could never have gained by more ordinary means. We know now that the luminous envelope surrounding the orb is a vast ocean of hydrogen gas, into which other gases are occasionally projected with inconceivable force for distances of hundreds of thousands of miles. The spectroscope also tells us that many of the metals known to us on this earth are in active combustion in the sun. Kirchhoff detected sodium, magnesium, calcium, iron, nickel, barium, copper, and zinc, and was doubtful with reference to one other metal, cobalt. This number has been much increased of late years, the discovery of many other elements being due to one of our own countrymen, Mr. Norman Lockyer, who, in one of his works, gives the following list:-- Sodium. Iron. Calcium. Magnesium. Chromium. Nickel. Barium. Zinc. Cobalt. Hydrogen. Manganese. Titanium. Aluminium. Strontium. Lead. Cadmium. Cerium. Uranium. Potassium. Vanadium. Palladium. Molybdenum. The marvellous revelations of the spectroscope are no longer dependent for their record upon the draughtman's hand, for by photography both the lines of Fraunhofer, as well as the bright lines of the metals, can be secured in the camera. The art of photography has indeed done much to bring spectroscopic research to its present forward position. I need hardly say that the records on the photographic plate are truthful, and far more reliable than the efforts of the most conscientious and accomplished artist. No two artists will produce images which exactly agree, they will each give the subject their own treatment, and stamp it with their own individuality. With the photographic plate all is different, the image will be perfect, nothing will be added to it and nothing taken away. All is stamped "upon a retina which never forgets." The instrument generally used for ordinary work in the laboratory is figured below.