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'Tis finished : retributive justice is dealt.
You may think me severe, but it's one of my ways;
It is felt evermore to the end of our days.
They may carve on the marble that graces my tomb :
THE STORY OF THE PRISM.
WHEN we see the brilliant colors re- was to find that the ray of light, after flected by the glass lustres and chande- passing through the prism, instead of beliers which are now so commonly used ing thrown upon the wall in the form of for decorative purposes, we seldom be- a round spot, was spread out into a stow a thought upon them, regarding beautiful colored ribbon ; this ribbon them as things too common, perhaps too being red at one end, and passing through trivial to be worthy of any particular at- orange yellow green and blue, to violet tention. We are content to know that at its other extremity. Upon this exa triangular piece of glass will exhibit periment is founded the theory of color, certain bright colors—they look very which with few modifications, still repretty, and it does not matter much how mains unquestioned. ihey happen to be there. This is the It was not until the beginning of the common way of dealing with the natural present century that this experiment of phenomena which meet us at every turn Newton's (repeated as it had doubtless in this wonderful world in which we live. been in the meantime by many philosoThe progress of civilisation, with all its phers) was found by Dr. Wollaston to triumphs of Science and Art, would in- possess certain peculiarities which defied deed have been slow, if not altogether at all explanation. He found that, by suba dead-lock, if every one had been con- stituting a slit in the shutter of the tent to treat such matters in this sum- darkened room for the round hole which mary fashion. But happily, this has not Newton had used, the ribbon of color, been the case, for certain intellectual or spectrum as it is now called, was ingiants have from time to time arisen, who tersected by certain dark lines. This have grappled with these things, and announcement, although at the time it have devoted their lives to their investi- did not excite much attention, led to gation.
further experiments by different investiSuch a one was Sir Isaac Newton, who gators, who, however, vainly endeavored just about two centuries ago, with rough to solve the meaning of these bands of appliances fashioned by his own hands, darkness. It was first observed by an inquired into the meaning of the colors optician of Munich that they never varied, to which we have just aliuded. We can- but always occupied a certain fixed ponot do better than quote his own words, sition in the spectrum; moreover he from a letter which he addressed to the succeeded in mapping them to the numRoyal Society in 1672; for his state- ber of nearly six hundred, for which reament is so clear that a child can easily son they have been identified with his understand what he means. 'I procured name, as ‘Fraunhofer's lines.' me a triangular glass prisme,' writes he, In 1830, when improved apparatus
to try therewith the celebrated phenom- came into use, it was found that the ena of colors. And in order thereto number of these lines could be reckoned having darkened my chamber and made by thousands rather than hundreds; but a small hole in my window-shuts to let their meaning still remained a puzzle to in a convenient quantity of the sun's all. By this time Newton's darkened light, I placed my prisme at his entrance, room with the hole in the 'windowthat it might be thereby refracted to the shuts ’ had been, as we have just said, opposite wall.'
greatly improved upon. The prism was He goes on to say how surprised he now placed in a tube, at one end of
which was a slit to admit the light, while the electric light. That is to say, the the retina of the observer's eye received light from the electric lamp was permitthe impression of the spectrum at the ted to shine through the vapor of the other end. This is the simplest form of burning metal under examination, formthe instrument now known as the spec- ing, so to speak, a background for the troscope, and which is, as we have shewn, expected lines. It was now seen that a copy in miniature of Newton's arrange- what before were bright bands on a dark ment for the decomposition of white light ground, were now dark bands on a bright into its constituent colors.
ground. This discovery of the reversal We must now go back a few years to of the lines peculiar to a burning metal, record some experiments carried out by when such metal was examined in the Herschel, which, quite independent of form of vapor, jed to the enunciation of the spectroscope, helped others to solve the great principle, that ‘vapors of the problem connected with the dark metals at a lower temperature absorb exlines. He pointed out that metals, when actly those rays which they emit at a rendered incandescent under the flame higher.' of the blow-pipe, exhibited various tints. To make this important fact more He further suggested that as the color clear, we will suppose that upon the redthus shewn was distinctive for each metal, hot cinders in an ordinary fire-grate is. it might be possible by these means to thrown a handful of salt petre. (This work out a new system of analysis. A salt is, as many of our readers will know, familiar instance of this property in cer- a chemical combination of the metal tain metals may be seen in the red and potassium with nitric acid-hence called green fire which is burned so lavishly nitrate of potash, or more commonly during the pantomime season at our nitre.) On looking through the spectrotheatres; the red owing its color to a scope at the dazzling molten mass thus preparation of the metal strontium, and produced, we should find that instead the green in like manner to barium. of the colored ribbon which the sunlight. Pyrotechnists also depend for their tints gives) all was black, with the exception not only upon the two metals just named, of a brilliant violet line at the one end. but also upon sodium, antimony, copper, of the spectrum, and an equally brilliant potassium, and magnesium. Wheatstone red line at the other end. This is the also noticed the same phenomena when spectrum peculiar to potassium ; so that, he subjected metals to the intense heat had we not been previously cognisant of of the electric current; but it was re- the presence of that metal, and had been served for others to examine these colors requested to name the source of the flame by means of the spectroscope. This was produced, the spectroscope would have done by Bunsen and Kirchhoff in 1860, enabled us to do so without difficulty.. who by their researches in this direction, We will now suppose that we again exlaid the foundation of a totally new amine this burning saltpetre under altered branch of science. They discovered that conditions. We will place the red-hot. each metal when in an incandescent state cinders in a shovel, and remove them to exhibited through the prism certain dis- the open air, throwing upon them a fresh tinctive brilliant lines. They also found supply of the nitre. We can now examthat these brilliant lines were identical ine its vapor, whilst the sunlight forms a. in position with many of Fraunhofer's background to it; when we shall see that, dark lines; or to put it more clearly, each the two bright colored lines have given bright line given by a burning metal place to dark ones. This experiment. found its exact counterpart in a dark will prove the truth of Kirchhoft's law so, line on the solar spectrum. It thus be far as potassium is concerned, for the came evident that there was some subtle molten mass first gave us the bright lines, connection between these brilliant lines and afterwards by examining the cooler and the dark bands which had puzzled vapor we saw that they were transformed observers for so many years. Having to bands of darkness; in other words this clue, experiments were pushed on they were absorbed. (In describing the with renewed vigor, until by some happy foregoing experiment, we have purposely chance, the vapors of the burning metals chosen a well-known substance, such as were examined through the agency of saltpetre, for illustration ; but in pracNEW SERIES.-VOL. XXVI., No. 3
tice, for reasons of a technical nature, a when the sun is low, and when therefore different form of potassium would be it is viewed through a thicker medium. employed.) Kirchhoff's discovery forms In this case the blue and green rays are by far the most important incident in the quickly absorbed, while the red pass history of the spectroscope, for upon it without difficulty through the denser are based the new sciences of Solar and mass of air, thus giving the setting sun Stellar Chemistry, to which we will now his blood-red color. It will now be direct our readers' attention.
readily understood how, by means of the The examination of the heavenly spectroscope, the existence of atmosphere bodies by means of the spectroscope has in the superior planets can be verified. not only corroborated in a very marvel- What a world of conjecture is thus lous manner the discoveries of various opened out to us! for the existence of atastronomers, but it has also been instru- mosphere in the planets argues that there mental in correcting certain theories and are seas, lakes, and rivers there subject giving rise to new ones. The existence to the same laws of evaporation as those of a feebly luminous envelope extending upon our own earth. And if this is so, for hundreds of thousands of miles be- what kind of beings are they who inhabit yond the actual surface of the sun, has these worlds? The moon shews no trace been made evident whenever an eclipse of atmosphere, so that we may assume has shut off the greater light, and so per- that if there be living beings there, they mitted it to be viewed. The prism has must exist without air and without water. shewn this envelope, or chromosphere as The lines given by the moon and planets it called, to consist of a vast sea of hy- being in number and position identical drogen gas, into which enormous flames with those belonging to the solar specof magnesium are occasionally injected trum, is a further proof, if any were with great force. (We need hardly re- needed, that their light is borrowed from mark that these facts are arrived at analogously by identifying the absorption The varied colors of the fixed stars lines with those given by the same ele- may be assumed to be due (from what ments when prepared artificially in the we have already stated with regard to laboratory.) This chromosphere can, metallic combustion) to their chemical by the peculiar lines which it exhibits in composition; and the spectroscope, hy the spectroscope, be made manifest when- the distinctive lines which it registers, ever the sun itself is shining.
renders this still more certain. Their The foregoing discovery has given as- distance from us is so vast, so immeastronomers the advantage-during a tran- urably beyond any conception of space sit of Venus—of viewing the position of that we can command, that the detecthe planet both before and after its pas- tion of their composition is indeed a sage across the sun's disc; for it is evi- triumph of scientific knowledge. It has dent that the presence of an opaque been calculated that if a model of the body in front of the chromosphere will universe were made in which our earth cut off the spectral lines in the path which were depicted as the size of a pea, the it follows; so that although the planet is earth itself would not be one-fifth large invisible its exact place can be noted. enough to contain that universe. From a comparison of these lines with If we marvel at the extraordinary skill those that can be produced in the labo- which has brought these distant spheres ratory, it is rendered probable that no under command of an analytical instruless than thirteen different metals are in ment, we must wonder still more when active combustion in the body of the sun. we are told that the spectra of these From certain geological appearances, it bodies can be brought within range of is conjectured that our own earth was the photographic camera, This has once in this state of igneous fusion, and lately been done by the aid of the most although our atmosphere is now reduced complicated and delicate mechanism; to a few simple elements, it must once the difficulty of keeping the image stahave possessed a composition as varied tionary on the sensitive collodion film as that of the sun. As it is, the air which during the apparent motion of the stars we breathe gives certain spectral lines. from east to west, having only just been These are much increased in number surmounted. This power of photographing the spectrum is likely to lead to very is obviously a great help to the diagnosis great results, for the records thus ob- of an obscure case. But in forensic tained are absolutely correct, and far medicine (where it might be assumed surpass in accuracy the efforts of the that this test would be of value in the inost skilful draughtsman. It must be detection of crime) the microscope can understood that in all these researches identify blood-stains in a more ready the spectroscope is allied with the tele- manner. scope, otherwise the small amount of The simple glass prism as used by light furnished by some of the bodies Newton, although it is the parent of the under examination would not be enough modern spectroscope, bears very little to yield any practical result.
resemblance to its gifted successor. The The clusters of matter which are complicated and costly instrument now called nebulæ, and which the most used consists of a train of several prisms, powerful telescopes have resolved inio through which the ray of light under exstars, are shewn by the prism to be noth- amination can be passed by reflection ing but patches of luminous gas, possi- more than once. By these means greatbly the first beginnings of uncreated er dispersion is gained ; that is to say, worlds. Comet-tails are of the same na- the resulting spectrum is longer, and ture, a doubt existing as to whether their consequently far easier of examination. nuclei borrow their light from the sun A detailed description of the instrument or emit light of themselves. We may would be impossible without diagrams, close a necessarily brief outline of this but enough has been said to enable the part of our subject by stating that it is reader to understand theoretically its possible that the spectroscope may some construction and application. day supplant the barometer, more than It will be understood that we have one observer having stated that he has but lightly touched upon a phase of discovered by its aid signs of coming science which is at present quite in its rain, when the latter instrument told a infancy. It is probable that many more flattering tale of continued fine weather. remarkable discoveries will in course of
We have 'merely shewn hitherto how time be due to the prism. Already, the spectroscope is capable of identify- within the past twenty years, four new ing a metal; but its powers are not lim- metals have by its aid been separated ited to this; for by a careful measure- from the substances with which they ment of the length of the absorption were before confounded; and although lines, a very exact estimate of the quantity they have not at present any commercial present can be arrived at. This method value, we may feel sure that they have of analysis is so delicate that in experi- been created for some good purpose not ments carried on at the Royal Mint, a yet revealed to us. There are signs that difference of one ten-thousandth part in the spectroscope will some day become an alloy has been recognised. Neither a recognised adjunct to our educational must it be supposed that the services of appliances. It is even now included the spectroscope are confined to metals, under the head of Chemistry in the exfor nearly all colored matter ean also be amination of candidates for university subjected to its scrutiny. Even the most honors, and there is no doubt that it will minute substances, when examined by gradually have a more extended use. the microscope in conjunction with the Many years hence, when generations of prism, shew a particular spectrum by School-Boards have banished ignorance which they can always be identified. from the land, the spectroscope may Nor does the form of the substance pre- become a common toy in the hands of sent any difficulty in its examination, for children, enabling them to lisp : a solution will shew the necessary absorption bands. Blood, for instance, can
Twinkle, twinkle, little star; be discovered when in a most diluted
We know exactly what you are. form. To the physician the detection of the vital fluid in any of the secretions
PICTURES IN HOLLAND, ON AND OFF CANVAS.
BY LADY VERNEY.
THERE is a curious difference between reaching the very end of the world. the two parts of the " Low Countries”- Then came the marshy flats, always at the “nether lands” formed of the ooze the mercy of a few inches' rise in the and mud deposited by the three great tidal rivers, and the intricate series of rivers, the Rhine, the Meuse, and the islands, which alter as the muddy chanScheldt, before entering the North Sea, nels of the there great rivers divide and and defended by a fringe of sandbanks change, the rushing waters eating away and “dunes," thrown up by the winds the low-lying lands they have themselves and the waves. Belgium is simply a flat, formed, and carrying them bodily into ugly, prosperous-looking, uninteresting the sea, against whose inroads the very country, not unlike the more common- existence of Holland is a continual strugplace parts of England; but the flatness gle of life and death. of Holland has infinitely more character Here, in this apparently remote corner in it, so that after passing the wide and of the earth, name after name was shoutturbid Scheldt, with its forests of ship- ed, as the stations succeeded each other ping, one feels as if in a new land. It is at short intervals, recalling some of the the difference between a merely plain most stirring scenes that the world has person and an ugly face full of character. ever known, and reminding one how in
We left Antwerp on a grey day, with the sixteenth and seventeenth centuries occasional gleams of light, the spire of this was the place where many of the the cathedral seeming for a time to grow greatest deeds in European history were taller and taller, as the perspective of enacted, and the most important negotidistance showed more clearly the true ns were conducted. relation of its height to the churches and Here was the centre of the great strughouses, the masts and chimneys, grouped gle for freedom, both religious and politround its central point - the delicate ical, won hardly for Europe at the cost tracery of its lofty pinnacles, rising 400 of such horrible sufferings to the inhabifeet above the little men who yet had tants of these industrious, well-doing ventured to build up that daring flight cities,-ingrained traders if ever any exof masonry heavenward.
isted, --who yet gave up the prosperity The dead flats, with trees and distant so dear to them for the sake of what to houses, and shifting islands of light on some seem only mere abstract questions ; the bright green meadows, passed quick- --where women and children helped in ly by, - living illustrations of the Dutch fighting the good fight, both actively and pictures with which we all are familiar; passively, not only enduring to the end the exquisite truth of which to nature the dreadful privations of the sieges, and strikes one at every turn, the land part exhorting their mankind not to yield, of the scene forming a mere line in the but even themselves fighting on the ramwhole subject, the sky and clouds, as at parts. Here such heads of the people sea, monopolizing three-fourths of the as William the Silent, Barneveldt, De composition, and requiring therefore in- Witt, Prince Maurice, and William III. finitely more care and thought in their revolved their great schemes of European arrangement than with other landscapes. policy, and moved the strings that moved
Presently came a series of small pine the world. woods, cut for fuel and the service of the After such a past, it seems strange rail before they could reach the age of how the current of political power has any beauty; with wide tracts of sandy, now, as it were, stranded Holland on her heathery common, and sour boggy bits, own mud-banks, and left her to her proswhere turf was being taken out, and perous trade, the commercial activity waste corners where more scrubby trees which fills the ports of Rotterdam, Dort, were attempting to grow. Few cottages, and Amsterdam with shipping and goods, no châteaux, hardly any inhabitants, the interior development of her agriculwere to be seen; it seemed as if we were ture over miles of flat green pastures,