sented. Copies from the same lithographic that each elementary substance—that is, a stones accompany the English edition of the substance which has not been split up, or memoir as are appended to the original, and decomposed, or out of which no two or more these are masterpieces of German artistic bodies differing in their properties have been skill. They are printed on six different obtained-whether it. be a gas, a solid, or a stones, with ink of six different tints, and liquid, may by heating be made to emit a reproduce with marvellous fidelity the ap- kind of light peculiar to itself, and different pearance which the solar spectrum presents from that given off by any other substance. when viewed through the magnificent Hei- Here, then, is the basis of this new method delburg instrument. of spectrum analysis-a science which deThese maps extend, however, over only monstrates the chemical composition of a one-third part of the visible portion of the body by the color or kind of light emitted solar spectrum, and it will, we fear, be long from it when heated. We now only need to before the other two-thirds are completely know, in order to understand the subject, surveyed, as the following note, telling of the the proper conditions under which bodies failing eyesight of the ingenious observer, can be made to develop this beautiful proptouchingly explains: "My drawing," he erty, by help of which their chemical natures says, "is intended to include that portion can be thus easily investigated, and analysis of the spectrum contained between the lines rendered not only independent of test-tubes, A and G. I must, however, confine myself but likewise of distance; for it is clear that at present to the publication of a part only so long as light can be seen, it matters not of this, as the remainder requires a revision, how far removed its source may be. The which I am unfortunately unable to under-sole condition which must be fulfilled in take, owing to my eyes being weakened by the continual observations which the subject rendered necessary."

Before it can be understood how these dark lines reveal the chemical composition of the solar atmosphere, it must be shown how the constitution of terrestrial matter can be ascertained by the examination of the nature of the light which such heated matter emits. That certain substances, when heated or burnt, give off peculiar kinds of light, has long been known; and this fact has been made use of by the chemist to distinguish and detect such substances. Thus compounds of the earth strontia, when burnt with gunpowder, produce the peculiar mixture well known as the "red fire" of the pyrotechnist; the salts of baryta give color to the green fires of the stage; and we all see in the Christmas game of snap-dragon that a handful of salt (chloride of sodium) thrown into the dish imparts to the flame a yellow color.

This property of substances to give off certain kinds of light was formerly only known to hold good for a few bodies; but the progress of science has taught us that it is not confined to one substance, but is applicable to all. We only require to examine a body under the proper conditions, in order to see that when heated it emits a peculiar and characteristic kind of light; so

order to attain the object, is that the body to be analyzed must be in a condition of luminous gas or vapor; for it is only in the gaseous state that each kind of matter emits the light peculiar to itself. It is somewhat difficult at first to understand how a gas or air can be heated until it emits light, and yet familiar instances are not wanting of such a condition of things. Flame, indeed, is nothing else than heated and luminous gas; and in the blue part of the flame of a candle, and in the lambent blue flame which plays on the top of a large fire, we have examples of a truly gaseous body heated until it becomes luminous.

The modes in which the various elements can be best obtained in the condition of luminous gases are very different. For the compounds of the metals of the alkalies and alkaline earths, it suffices to bring a small quantity of one of their salts into a flame of a spirit lamp, or into a gas flame. The salt then volatilizes, or becomes gaseous; and this vapor, heated to the temperature at which it is luminous, tinges the flame with a peculiar color. For the compounds of the other metals, such as iron, platinum, or silver, a much higher temperature is needed; whilst for bodies such as air and hydrogen, which are gases at the ordinary temperature, a different mode of manipulation is necessary.

I

N

compound in front of the slit through which the light falls on to the prisms, and thence into the telescope, we shall see the spectrum of sodium. We notice that it consists simply of two very fine bright yellow lines placed close together, all the rest of the field being perfectly dark. On investigation we find that all the compounds of the metal sodium give these two lines, and no other substance is met with in whose spectrum these lines

In order to become acquainted with the exact nature of the light which bodies in the condition of luminous gases emit, their light must be examined otherwise than by the naked eye. The same kind of apparatus is used in this investigation which Fraunhofer and Kirchhoff applied to the investigation of solar light; in short, the distinctive qualities of these luminous gases are ascertained by their spectra. Then only is it that the full beauty of this property of matter be- occur. So excessively delicate is this indicomes apparent, and the character of each elementary body is written down in truly glowing language-language different for every element, but fixed and unalterable for each one, as to the interpretation of which no variety of opinion can possibly exist.

cation of sodium--that is, so small a quantity of sodium salt suffices to bring forth a flash of these bright lines-that we discover sodium everywhere, in every particle of dust; in the motes visible in the sunbeam. We cannot touch any substance without imTo Professors Bunsen and Kirchhoff sci- parting to it some soda salt from our hands. ence is mainly indebted for the examination Hence it appears that Professor Bunsen was of this hitherto hidden language of nature. able to detect the presence of one one hunThese philosophers undertook an investiga- dred and eighty millionth part of a grain of tion of the "Spectra of the Chemical Ele- soda; and we learn without astonishment ments," and nobly have they carried out that common salt, derived from the ocean their intention; unfolding a vast store of which covered two-thirds of the earth's surnature's secrets to the knowledge of man- face, is always present in the atmosphere in kind, and revealing the existence of much a very finely divided solid form, which doubtmore yet to be learnt in unlimited fields | less produces most important effects on the which promise a rich harvest of discovery to animal economy, and probably on all the the patient and exact inquirer. Seldom in- phenomena of life. deed has it been the privilege of men in a single discovery to found a science, or to open a subject so pregnant with important results as that of spectrum analysis.

If a small quantity of a potash salt, instead of the soda, be placed in the flame, it will be tinged purple; the potash spectrum consists of a portion of continuous light in Those alone who are acquainted with the the centre, bounded by a bright red and a practical details of the science of Chemistry bright violet line at either end. This peculwill be able fully to appreciate the grand iar appearance is alone caused by the comchange which the introduction of this new pounds of potassium, and is produced by all method effects in the branch of their science the salts of this metal. So, too, with each devoted to analysis. Qualitative analysis metal we notice peculiar bright-colored thereby undergoes a complete revolution; bands, or lines, which are so distinct and the tedious operations of precipitation and characteristic that a glance through the telfiltration must now be superseded by the escope reveals, to an experienced eye, the rapid observation of the spectra of the col-presence of each of the metals of the alkalies ored flames by which the presence of the most minute trace of the substance-far too small to be found by the older and coarser methods can be surely and clearly detected. Let us endeavor to form an idea of the appearance of the peculiar spectra thus obtained; the most complete or eloquent description must, however, fail to give more than a bare idea of the reality.

and alkaline earths, when they occur or are combined together even in the minutest quantities. For none of these bright lines overlap or interfere with any other; the lines of each metal when all are present together, appear perfectly distinct. It is a hopeless task to endeavor by words to express the beauty of the phenomena which in this branch of science present themselves to the In the first place, if we look through the beholder; as well might we attempt to contelescope of Kirchhoff's instrument, having vey by description, to one who had not witplaced a flame colored yellow by a sodium nessed those scenes, the grandeur of the

high Alps, or the majesty of the flight of a hesitated not a moment, but began to evapcomet through the heavens. Suffice it to orate forty tons of the water in order to get say, with Kirchhoff, that the appearances enough material to separate out his new here noticed "belong to the most brilliant metal, and examine all its chemical relations. optical phenomena which can be observed." No sooner, however, had he obtained more Professor Bunsen thus describes what he saw than a mere trace of the new substance, than when he placed a mixture of the salts of all he found that with it was associated a secthe metals of the alkalies and alkaline earths ond new metal. From the forty tons of the into the flame, and observed the spectra thus water in question Bunsen got only about one produced :hundred and five grains of the chloride of "I took," he says, a mixture, consisting one metal, and one hundred and thirty-five of chloride of sodium, chloride of potassium, grains of the chloride of the other; in such chloride of lithium, chloride of calcium, minute quantities do these substances occur! chloride of strontium, chloride of barium, Yet, thanks to the skill and patient industry containing at most one one thousandth part of the great chemist of Heidelberg, these of a grain of each substance. This mixture difficulties were triumphantly overcome, and I put into the flame, and observed the result. First, the intense yellow sodium lines ap- we now possess a chemical history of these peared on a background of a pale continuous two new metals as complete and well authenspectrum; as these began to be less distinct, ticated as that of the commoner alkalies. the pale potassium lines were seen, and then The names wisely chosen for these substances the red lithium line came out, whilst the indicate the nature of their origin, and point barium lines appeared in all their vividness. out the property by help of which they were The sodium, lithium, potassium, and barium salts were now almost all volatilized, and after discovered. Bunsen calls one of them "Ca few moments the strontium and calcium sium," from cæsius bluish gray, because the lines came out as from a dissolving view, spectrum of this metal is distinguished by gradually attaining their characteristic bright- two splendid violet lines; the other he named ness and form." "Rubidium," from rubidus dark red, owing to the presence of two bright red rays at the least refrangible extremity of its spectrum. Since the publication of the discovery of these metals, their salts have been found to be pretty commonly diffused; but, owing to their close resemblance to the compounds of potassium, they were not recognized as separate substances; in fact, had it not been for this new method, we should not have been able to distinguish them from the well-known alkali potash. Caesium and Rubidium occur in the water of almost every salt spring; and they have likewise been found in the ashes of plants, especially in those of beet-root, so that they must be contained in the soil; but in all these cases the quantity in which they are found is very minute. The mineral lepidolite contains a certain quantity of Rubidium, which now may be obtained by the pound; but Cesium is still extremely rare. It is satisfactory to learn that in a similar way the existence of another new metal has been pointed out by Mr. Crookes. This body is characterized by a spectrum containing one bright green band, and has been called "Thallium."*

The most striking example of the value of this new power of analysis, and of its probable results, is that of the discovery of two new alkaline metals by Bunsen. This distinguished chemist, in examining the spectra of the alkalies contained in the mineral waters of Dürkheim in the Palatinate, observed some bright lines that he had not seen in any other alkalies which he had investigated. He was sure that no other metals but those of the alkalies could be present, because by well-known chemical processes, he had separated every other kind of metal. Hence he concluded that these new lines indicated the presence of an alkaline metal whose existence had as yet been overlooked. In fact, just as Adams and Leverrier, from the perturbations of the planet Uranus, predicted the existence of Neptune, so Bunsen, from the perturbations seen in the spectra of the alkalies, predicted the existence of a new member of the large family of the elementary bodies. So certain was Bunsen of his method, and so confident was be that his bright lines could not fail him, that, although the weight of substance from which he obtained his result only amounted to the one one thousandth part of a grain, he

*This new element has lately been prepared in somewhat larger quantities by M. Lamy from the

scientific basis, by applying to it the modern methods of exact research.

In an article like the present it is impossible to enter minutely into the details of such discoveries, or even to mention more For the purpose of obtaining the peculiar than the most striking points by way of il- spectra of iron, platinum, copper, and most lustration. Enough has, however, been said of the other metals, these metals must be to show the enormous fertility of this field exposed to a much higher temperature than of research, and to give an idea of the prin- that of a gas flame, to which they impart no ciples upon which the method depends. We color. This high temperature is best atanticipate, more especially, important results tained by the use of the electric spark. So to the art of medicine from the application great, indeed, is the heat developed by this of this analytical process to mineral waters, as agent, that a single electric discharge past they are termed, noted for their therapeutic through a gold wire dissipates the metal at qualities. The composition of these waters, once in vapor. Our illustrious Faradayther apparently inexhaustible faculty of re- the founder of so many branches of electriproduction, their modes of affecting the hu- cal science-first showed that the electric mar frame in various states of health and dis- spark was produced by the intense ignition ease, are only known as yet empirically. Yet of the particles composing the poles; and it is impossible to doubt or deny that waters, Professor Wheatstone proved that if we look like those of Carlsbad, Aix-la-Chapelle, or at the spark proceeding from two metallic Bagnères de Luchon, contain certain agents poles, through a prism, we see spectra of the most powerful sanative character, containing bright lines which differ acwhich the means of chemical analysis hith-cording to the kind of metal employed. ero employed do not appear to have reached." These differences," said Wheatstone, writIt is extremely probable that the application ing in 1834, "are so obvious, that any one of spectral analysis to the elements contained in these springs will bring them within the range of accurate medical knowledge, and perhaps extend the resources of medicine itself. The field of spectrum analysis was not wholly untrodden until it was explored by the two German professors. Even so long ago as 1826, Mr. Fox Talbot, a gen- The large number of bright lines which tleman whose name is honorably associated are seen in the spark spectrum are not all with discoveries in that most beautiful of the caused by the glowing vapor of the metal modern applications of science to art-Pho- forming the poles; a portion of them protography-made some experiments upon the ceed, as Angström first pointed out, from the spectra of colored flames, and pointed out particles of gas or air, through which the the advantages which such a method of anal- spark passes, becoming luminous also, and ysis would possess. Professor Wheatstone, emitting their own peculiar light. Thus, if Mr. Swan, Sir David Brewster, and Profes- we examine the spectrum of an electric spark sor W. Allen Miller in our own country, and passing from two iron poles in the air, we see Angström, Plücker, Masson, and others on at least three superimposed spectra, one of the Continent, have likewise contributed to the iron, one of the oxygen, and a third of our knowledge of this subject; but whatever the nitrogen of the air. By help of a little may have been done by, others for the estab-mechanical device, it is easy to distinguish lishment of the new method, it must be ad- between the air lines and the true metallic mitted that the names of Bunsen and Kirch-lines, and in this way to detect the various hoff will justly go down to posterity as the founders of the Science of Spectrum Analysis; for they first established it on a firm

residues of the Belgian sulphuric acid chambers.
He finds that in its specific gravity and outward
properties it closely resembles the metal lead, but
that it possesses very peculiar chemical character-
istics.

metal may instantly be distinguished from others by the appearance of its spark; and we have here a mode of discriminating metallic bodies more ready than a chemical examination, and which may hereafter be employed for useful purposes." This has, indeed, turned out to be a true prediction.

metals. So certain and accurate is this method that Professor Kirchhoff has, without difficulty, been able to detect and dis tinguish the presence of minute traces of the

*The spectra of the permanent gases, as well as those of the other non-metallic elements, have been3 accurately examined by Professor Plücker, of Bonn.

rare metals Erbium and Terbium, as well as solar lines was well known, yet the exact Cerium, Lanthanum, and Didymium, when connection between the two phenomena was they are mixed together; a feat which the not understood until Professor Kirchhoff, in most experienced analyst would find it al- the autumn of 1859, investigated the submost impossible, even after the most length-ject. Nevertheless, before he gave the exened and careful investigation, to accomplish act proof of their connection, some few bold with the older methods. minds had foreseen the conclusions to which these observations must lead, and had predicted the existence of sodium in the sur. Foremost among these stand Professors Stokes and William Thomson, and the Swedish philosopher Angström. It is, however, to Kirchhoff that we are indebted for the full and scientific investigation of the subject, and he must be considered as the founder of the science of solar and stellar chemistry.

In endeavoring to form an idea of the present and future bearings of the science of spectrum analysis as applied to the investigation of terrestrial matter, we must remember that the whole subject is as yet in its earliest infancy; that the methods of research are scarcely known; and that speculations as to the results which further experiments will bring forth, are therefore, for the most part, idle and premature. We may, however, express our opinion that a more intimate knowledge of the nature of the socalled elements, if it is to be attained at all, is to be sought for in the relations which the spectra of these substances present; and if 66 a transmutation " of these elementary bodies be effected, as is by no means impossible, it will be effected, by help of the new science of spectrum analysis. That we shall thus gradually attain a far more accurate knowledge of the composition of the earth's crust than we now possess, is perfectly certain; nor is it less certain, that with the progress of the investigation, other new elementary bodies will be added to our already somewhat overgrown chemical family.

Wishing to test the accuracy of this frequently asserted coincidence of the bright metallic and dark solar lines with his very delicate instrument, Professor Kirchhoff made the following very remarkable experiment, which is interesting as giving the key to the solution of the problem regarding the existence of sodium and other metals in the sun :—

"In order to test in the most direct manner possible the frequently asserted fact of the coincidence of the sodium lines with the lines D, I obtained a tolerably bright solar spectrum, and brought a flame colored by sodium vapor in front of the slit. I then saw the dark lines D change into bright ones. So long ago as 1815, Fraunhofer made the The flame of a Bunsen's lamp threw the important observation, that the two bright bright sodium lines upon the solar spectrum In order to yellow lines which we now know to be the with unexpected brilliancy. sodium lines, were coincident with, or pos- the solar spectrum could be increased withfind out the extent to which the intensity of sessed the same degree of refrangibility as, out impairing the distinctness of the sodium two dark lines in the solar spectrum called lines, I allowed the full sunlight to shine by Fraunhofer the lines D. A similar coin- through the sodium flame, and to my astoncidence was observed by Sir David Brew-ishment I saw that the dark lines D appeared ster, in 1842, between the bright red line of potassium and a dark line in the solar spec-mond's trum called Fraunhofer's A. The fact of the coincidence of these lines is easily rendered visible if the solar spectrum is allowed to fall into the upper half of the field of our telescope, whilst the sodium or potassium spectrum occupies the lower half. The bright lines produced by the metal, as fine as the finest spider's web, are then seen to be exact prolongations, as it were, of the corresponding dark solar lines.

Although the fact of the coincidence of several bright metallic lines with the dark

with an extraordinary degree of clearness. I then exchanged the sunlight for the Drummond's or oxy-hydrogen lime-light, which, like that of all incandescent solid or liquid bodies, gives a spectrum containing no dark lines. When this light was allowed to fall through a suitable flame colored by common salt, dark lines were seen in the spectrum in the position of the sodium lines. The same phenomenon was observed if instead of the which being heated in a flame was brought incandescent lime a platinum wire was used, to a temperature near its melting point by passing an electric current through it. The phenomenon in question is easily explained upon the supposition that the sodium flame