The Spectroscope.
Next we come to one of the most astonishing and beautiful optical instruments ever made by the hand of man. It is called the Spectroscope, because it deals with a certain arrangement of rays which is called a “spectrum.” Many years ago Newton discovered the cause of the lovely colours which deck the rainbow, and the fact that, by passing a ray of white light through a prism, it was decomposed into seven colours, which invariably came in the following order—Red, Orange, Yellow, Green, Blue, Indigo, and Violet. He also discovered that, by looking at that coloured band through another prism arranged in a different manner, the decomposed rays were again brought together, and white light was the result.
Newton had thrown the light on the prism through a round hole, but some time afterwards Dr. Wollaston employed a narrow slit for the purpose, and then found that the spectrum was traversed by dark lines which never changed their places. On these lines depend all the discoveries that have been made by the aid of the Spectroscope. The chief of them are designated by the letters of the alphabet. (See page 300.)
It was soon found out that if burning gases were viewed with the Spectroscope, lines were still seen, but they were bright instead of dark, and that they invariably occupied the place of one or more of the dark lines shown by the spectrum of sunlight. Then it was discovered that these burning gases absorbed or stopped out the light in the solar spectrum, and from that moment the science rapidly advanced.
At the present day the Spectroscope not only determines the metals which exist in the sun, but also those of the fixed stars. It even analyzes the constitution of double stars, and shows the reason why one star should be red and the other green.
One of the most astonishing discoveries in astronomy was due to the Spectroscope.
During the month of May, 1866, one of the stars in the Northern Crown (Corona Borealis) was seen to undergo a rapid change. It was originally one of the tenth magnitude, but in a short time increased in size and brilliancy until it nearly equalled Sirius, Capella, or Vega. It remained bright for some time, and then rapidly faded until it resumed its former size.
How this change was effected we never should have known but for the Spectroscope. No sooner, however, was this instrument pointed at the star than there appeared in the spectrum the three well-known lines—red, green, and violet—which denote burning hydrogen. There was no doubt on the matter, and the Spectroscope showed us that we were witnessing a conflagration the like of which was never seen or scarcely imagined.
Supposing our sun, which is known to be one of the stars, and about which there are vast volumes of hydrogen gas, were to blaze out in a similar manner, the result would be that the whole of the planets would be consumed in a few seconds, and converted into gases. In an instant every living thing would be swept off the surface of the earth by this fearful heat, and, as Mr. Roscoe says, “our solid globe would be dissipated in vapour almost as soon as drops of water in a furnace.” So, as Mr. Huggins observes, the old nursery rhyme,—
“Twinkle, twinkle, little star,
How I wonder what you are,”—
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.
So marvellously delicate is the instrument with regard to blood, that it detects the thousandth part of a grain of colouring matter in a blood-stain.
If upon the spectrum were printed the word BLOOD in the largest and blackest of capitals, it could not be more legible to an ordinary reader than are the two blood-bands to the eye of a spectroscopist. There is nothing like them in nature, and whether it be by association of ideas, or by absolute fact, these two bars have a strangely menacing look about them. Not only that, but if the blood should be that of a person suffocated with carbonic acid gas, the Spectroscope will say so.
Some years ago a man owed his life to the Spectroscope. A mysterious murder had been committed, and the police had arrested a man who was found near the spot. He could give no intelligible account of himself, and the sleeves of his coat and a part of his waistcoat were deeply stained with a red substance just like clotted blood. A piece of each garment was cut off and given to a well-known spectroscopist, who tried the red matter in the instrument, and at once declared it not to be blood. What it was he had not time to ascertain, so he sent it to a brother in science, who, after examination, pronounced it to be red gum.
By degrees, the man, who had been intoxicated when arrested, stated that he had been to see a friend who was a journeyman hatter. It was then found that he had been leaning on the workman’s board, and so had carried off some of the gummastic with which hats are stiffened. Had it not been for the infallible Spectroscope, the man might have lost his life.
Thus we see that the Spectroscope is the elephant’s trunk of optics, equally fitted for the greatest and smallest, the farthest and nearest, of objects. It is equally at home in earth and sky. When attached to the telescope, it reveals the constituents of the stars, and, when affixed to the microscope, it shows us the colouring matter of a green leaf. It produces the best steel, and detects adulteration in wine. And, lastly, as we have seen, it turns lawyer, and settles the evidence by which the life of a man is lost or saved. It can determine the purity of the smallest coinage, and tell us why a star changes in magnitude.
Yet all these wondrous revelations are made by a few prisms and a magnifying-glass. I possess a Spectroscope, made and presented to me by Mr. J. Browning, the celebrated optician. This astonishing instrument is only three inches long, and half an inch in diameter, so that it can be carried in the waistcoat pocket. I always keep mine in a finger of a white kid glove, which is amply sufficient for it. Yet it gives the spectrum of the sun with its principal lines, will detect the fraudulent wine merchant, and could have decided whether the accused man should be acquitted or hanged.
Marvellous and mighty as is this engine, it lay concealed in Nature ever since the sun’s rays shone upon earth and a drop of water existed. The Rainbow is nothing but a vast spectrum, a transverse slice of which would be a good representation of the coloured band which is shown in the instrument. It is prefigured in the ever-shifting rainbows of the water-fall and fountain, which latter may even be seen in the fountains of Trafalgar Square, while at the Crystal Palace their beauty has long been noticed.
There is not a dewdrop which is not a miniature Spectroscope, as it glitters with its wondrous iridescence in the rays of the rising sun; there is not an opal with its shifting hues, nor the splendour of the soap-bubble, nor the nacre of the common river mussel or the ormer shell, which does not owe its beauty to the same principles which govern the Spectroscope. Every green leaf, and blue or pink or yellow petal, every varying tint of the mackerel sky, every blaze of sunset and bluegrey of sunrise, owes its beauty to those wondrous laws of light which had been hidden for so many centuries, until they were unveiled by the simple prism of the Spectroscope. As in so many instances, the revelation lay concealed until the coming of the revealer, whose inspired hand raised the dark veil of centuries.