is no longer tenable, for we really do know the composition of the stars.
The Spectroscope not only tells us the substance of which the sun and the most distant stars are made, but gives us the same information about the “gay motes that people the sunbeam.” It tells us that they are common salt in very minute particles. They have been dashed into the air by the winds as spray, and then dispersed over the whole globe. This is one reason why we have so much salt in our bodies, and why the blood and the tears are so salt.
It is also applied to the arts. The well-known Bessemer process consists in pouring melted iron into a peculiarly shaped vessel called a “converter,” and blowing air through it for the purpose of burning out the carbon. From the mouth of the converter issues a volume of magnificent flames, and at a certain moment the skilled workman who directs the process inverts the vessel and pours out the steel. A very few seconds too soon or too late would spoil the whole of the metal, in the former case it being simply brittle cast-iron; and, in the second, becoming so thick that it could not be poured out.
Only a few workmen could judge rightly the exact point at which to shut off the air-blast. They watched the flame, and by some change in it, too slight to be noticed by any except experienced eyes, knew the moment when the iron was converted into steel.
Such men could, of course, demand any wages they liked, and, by striking, stop the whole works. The Spectroscope, however, performed this delicate discrimination far better than the best workman. When directed to the flame, the bright lines indicating carbon are seen in the spectrum. When the blast has continued for some twenty minutes, the carbon lines suddenly disappear, showing that the carbon has been burned out, and giving to the workman the signal to shut off the air-blast.
Another discovery was, that liquids gave dark lines, technically termed absorption bands, of different widths and in different parts of the spectrum. Even liquids which had no perceptible colour threw bands as bold as those which were coloured, while coloured liquids threw totally different bands, irrespectively of their own colour.
For example, the green colouring matter of leaves, called chlorophyll, throws a single broad band on the extreme left—i.e. across the red part of the spectrum—so far back, indeed, that it is not easily seen at first.
Then, suppose that we make some pale solutions of red substances, such as carmine, magenta dye, port wine, logwood, permanganate of potash, and blood, it is possible to have them so exactly resembling each other that not even the microscope can discriminate between them; yet the Spectroscope instantly detects the colouring matter of each solution.
The instrument is, therefore, invaluable in detecting adulterations of wine. For example, supposing that red wine is suspected of owing its redness to logwood, and not to the genuine grape, a drop is mixed with water and viewed through the Spectroscope, which instantly tells whether the colouring matter is grape or logwood. And as, by photography, the spectrum can be exactly copied, an indelible record is procured of the true nature of the object.