We have merely shewn hitherto how the spectroscope is capable of identifying a metal; but its powers are not limited to this; for by a careful measurement of the length of the absorption lines, a very exact estimate of the quantity present can be arrived at. This method of analysis is so delicate that in experiments carried on at the Royal Mint, a difference of one ten-thousandth part in an alloy has been recognised. Neither must it be supposed that the services of the spectroscope are confined to metals, for nearly all coloured matter can also be subjected to its scrutiny. Even the most minute substances, when examined by the microscope in conjunction with the prism, shew a particular spectrum by which they can always be identified. Nor does the form of the substance present any difficulty in its examination, for a solution will shew the necessary absorption bands. Blood, for instance, can be discovered when in a most diluted form. To the physician the detection of the vital fluid in any of the secretions is obviously a great help to the diagnosis of an obscure case. But in forensic medicine (where it might be assumed that this test would be of value in the detection of crime) the microscope can identify blood-stains in a more ready manner.
The simple glass prism as used by Newton, although it is the parent of the modern spectroscope, bears very little resemblance to its gifted successor. The complicated and costly instrument now used consists of a train of several prisms, through which the ray of light under examination can be passed by reflection more than once. By these means greater dispersion is gained; that is to say, the resulting spectrum is longer, and consequently far easier of examination. A detailed description of the instrument would be impossible without diagrams, but enough has been said to enable the reader to understand theoretically its construction and application.
It will be understood that we have but lightly touched upon a phase of science which is at present quite in its infancy. It is probable that many more remarkable discoveries will in course of time be due to the prism. Already, within the past twenty years, four new metals have by its aid been separated from the substances with which they were before confounded; and although they have not at present any commercial value, we may feel sure that they have been created for some good purpose not yet revealed to us. There are signs that the spectroscope will some day become a recognised adjunct to our educational appliances. It is even now included under the head of Chemistry in the examination of candidates for university honours, and there is no doubt that it will gradually have a more extended use. Many years hence, when generations of School-Boards have banished ignorance from the land, the spectroscope may become a common toy in the hands of children, enabling them to lisp:
Twinkle, twinkle, little star;
We know exactly what you are.
[THE ROMANCE OF A LODGING.]
IN TWO CHAPTERS.—CHAP. I.
'Where to, ma'am?' inquired cabby as he opened the door of his vehicle to a lady and her son who had just arrived by the evening train at Victoria Station.
'I want apartments somewhere in the neighbourhood of Chelsea; drive on until you find them: they are procurable, I suppose?' the lady replied as she took her seat.
'I do hope we may find a lodging,' she remarked to her companion, after they had been driving what appeared to her a very long time. The lad made no reply, being of a phlegmatic temperament, that finds speech an exertion unless distinctly necessary.