Scientific Chronicle.

CATHOLIC SCIENTIFIC MEETING.

THE International Congress of Catholic Scientists will meet in Paris on the 8th of this month.

The brief of his Holiness issued last May, the untiring exertions of Mgr. d'Hulst, President of the Paris Catholic University, and the prompt coöperation of scientists of many lands have combined in assuring for it a splendid success.

The organizing committee of the Congress, Mgr. d'Hulst presiding, had a meeting on November 22d, 1887. It was then officially announced that 430 favorable answers had been received, 285 from France, and 145 from other countries. The list of honorary members enrolled up to that date contained 162 names of eminent men, among them over 40 cardinals. It was also announced at the same meeting that papers to the number of 60 on various scientific topics had already been handed in to the Chairman. This encouraging state of affairs at a date so far in advance of the meeting of the Congress, gave bright promise of the favorable auspices under which the event itself would be inaugurated. We look forward then with lively interest to the reports of the transactions of the Congress, feeling confident that, once more, practical proof will be given of the benefits which science derives from the safe-guard of religion.

There is one subject which we would especially desire to see taken in hand by some of the able men whom the Congress will bring together; we mean the refutation of Darwinism. A baneful and growing fashion is at present in vogue amongst a large class, particularly of English and German speaking scientists, of declaring themselves Darwinists even when the profession seems altogether foreign to the matter with which they are dealing. We could not understand, for instance, why an eminent mathematician such as Prof. Sylvester is known to be, should make a profession of faith of this kind in the course of a purely mathematical article, which some time ago appeared under his name. The origin of the fashion would seem to be, that not a small portion of the scientific press of these countries systematically ignores whatever does not emanate from a Darwinian source.

The mischief accruing from all this is easily perceived. It leads uninformed readers to infer that the Darwinian hypothesis is all but universally adopted by the world of science. In reality, if we consider the whole of the scientific world, the reverse is nearer the truth. In the greater part of continental Europe the adherents of the system are conspicuously few. The old French school is opposed to it, all the great professors of the Sorbonne and of the Collège de France reject it. Among

the materialists of France, it is true, some ardent admirers of the system are on the point of establishing a new chair in which their views may be inculcated. The French Government, which is only too eager to promote anything even seemingly opposed to Catholic traditions, will, no doubt, lend every assistance to the movement, and before long we may expect to find some second-rate naturalist of the Darwinian type exalted to the position. In Germany, we find among prominent scientists the same general view. In the Congress of German Naturalists and Physicians at Wiesbaden last fall, a trenchant refutation of Darwinism was delivered by the illustrious Prof. Rudolph Virchow. We regret that its length precludes the possibility of reproducing it in these pages, and it would be an injury to it to summarize it or otherwise alter its form. We need not be apprehensive of exaggerating the authority of this remarkable man. As the originator of "Cellular Pathology" and of the present science of tumors, his position in the ranks of science is unequivocal, and his reputation as a master of every subject he enters into is unchallenged. His special field of study, too, rendered him peculiarly fitted to meet the arguments of the Darwinists with contradictory facts, which his own investigations had scrupulously verified. Let us hope that some of the Catholic scientists will follow in the same lines, and show in a still clearer light the baseless and hollow character of the suppositions on which the showy structure of Darwinism is erected.

SPECTRUM ANALYSIS AND THE ROWLAND GRATINGS.

THERE is perhaps no branch of physical science which, for the rapidity of its development and the importance of its discoveries, can be compared with spectrum analysis. Not thirty years have elapsed since the investigations of Kirchoff and Bunsen, yet to the method of analysis which they introduced we owe some of the most striking discoveries of the present century. The spectroscope has not only led to the finding of several new chemical elements, but it has also proved of great assistance in astronomy. By its means, many of the elements composing the sun have been ascertained, and the question of the solar spots has been almost completely answered. The red prominences which may be seen around the solar disk during a total eclipse, have been observed by the spectroscope even in full daylight; they have revealed to the observer their constituent elements, and, by a slight change in the position of their spectral lines, they have made known the velocity with which the incandescent gas bursts forth from the body of the sun. By spectrum analysis, astronomers have ascertained that some of the nebulæ are huge volumes of glowing gases, and are, therefore, not composed of separate stars; they have found that most of the so-called fixed stars are really in rapid motion, and have actually measured their velocity in the direction of our line of sight.

Now, what is this spectrum analysis, and upon what principles does it

rest? When a beam of sunlight, entering a dark room through a narrow slit in the window-blind, is allowed to fall upon a prism, the light will be refracted, i.e. turned aside from its straight course. Not only will the sunlight be refracted, but it will also be decomposed into its constituent colors. For, since the different colors are unequally refrangible, some will be turned from the straight course more than others; hence the different colors will, after refraction, follow slightly divergent paths, and if they fall upon a white screen they will form a ribbon of light containing, in regular succession from violet to red, all the colors of the rainbow. This ribbon, or band, is called the solar spectrum. If any other kind of light be allowed to pass through a prism in the same manner, it will form its own spectrum, differing from that of sunlight, and by carefully examining any spectrum we can ascertain the kind of light which has caused it.

For this careful examination, however, we need a more elaborate arrangement than a prism and a white screen. The instrument employed is called a spectroscope. Spectroscopes differ widely in their construction, but they generally consist of three parts: 1st, a prism, to form the spectrum; 2d, a collimator, to direct a narrow beam of light upon the prism; 3d, a small telescope, to view the spectrum. The collimator is very much like a telescope with a narrow slit instead of an eyepiece ; by widening or narrowing the slit, the amount of light introduced may be increased or diminished at pleasure.

Let us consider the manner in which the spectroscope is used for the analysis of light. Suppose we place in front of the collimator a flame which is strictly monochromatic, containing, for example, no color but red. The light, passing through the slit and meeting with the prism, will be simply bent from its course; as there is only one color, all the light will be refracted to the same extent, and the spectrum will consist of a single red line. Suppose, however, that the flame, instead of being monochromatic, contains two colors,-for example, red and yellow. The naked eye cannot distinguish the two colors in the flame, but when the light passes through a spectroscope the colors are unequally refracted, and thus form a spectrum consisting of two bright lines,-the one red, the other yellow. If the flame contains three colors, its spectrum will consist of three bright lines, and in general every additional color in the flame will produce an additional bright line in the spectrum.

Spectra such as those we have just described are called "bright band spectra," and their use in analyzing substances may be readily seen. Each one of the chemical elements, if burned, will produce its own peculiarly colored flame, giving rise to its own characteristic spectrum, i.e., its own system of bright lines. Rarely can one distinguish, by the mere color, the flame of one element from that of another, and the difficulty is increased a hundredfold when several elements are burned together. The spectroscope, however, compels each element to make known its presence. So delicate is this method of analysis, that the burning of the one two hundred millionth of a grain of sodium will give the characteristic spectrum of that metal.

The more numerous the different colors in the light examined, the

more numerous will be the bright lines in its spectrum. Now white light contains every color. Accordingly, if white light be analyzed, there will be so many bright lines that they will coalesce into an uninterrupted band of light, very much resembling the solar spectrum, yet differing from it in a manner to be explained later. These uninterrupted spectra are called "continuous spectra." They are given by any incandescent solid or liquid, and also by any gas burning under great pressure. The solar spectrum belongs to a third class; it is one of the "dark band spectra." To a casual observer the spectrum of sunlight appears to be continuous, but on closer examination it is found to be interrupted. by a great number of dark bands. Fraunhofer, in the year 1815, was the first who carefully investigated these dark bands, and they are still known as the "Fraunhofer lines." Their existence in the solar spectrum was a puzzle to physicists, until Kirchoff explained them in the year 1859. He placed a calcium-light in such a position that the rays. from it, before reaching the collimator of his spectroscope, had to pass through a flame colored by sodium vapor. Then, looking into the spectroscope, he found that the bright lines due to the sodium were absent from the spectrum, and that their place was supplied by dark bands. While the white light was passing through the sodium flame, the vapor of sodium had absorbed just those rays which it was itself capable of emitting. Extending his investigations, Kirchoff discovered that what was true of sodium vapor was true of any other vapor, and that every black band spectrum could be explained by the absorption of certain rays of light. Hence the black band spectra are called sometimes “absorption spectra."

The relations which the various classes of spectra have, one with another, may be seen at a glance. Incandescent solids and liquids, as well as gases under great pressure, give continuous spectra. Vapors and gases, when not compressed, give bright band spectra ; and these spectra are different for different substances. The dark band spectrum is given by white light which has passed through an incandescent vapor, and has had some of its light absorbed.

Whenever the spectrum is employed for the purpose of analysis, the exact position of the lines becomes a matter of the greatest importance. At present, there are more than three thousand lines recognized in the solar spectrum; hence, unless the position of each is determined with accuracy, there is great danger of mistaking one for another, and thus rendering the observation useless. The exact determination of the place of each line becomes still more necessary when the spectroscope is used to measure the motion of the stars, for this motion is calculated from a very slight change in the position of the lines. Unfortunately, when the spectrum is formed by means of a prism, the relative distance apart of the lines will depend upon the material of the prism, and, even in the same prism, will vary with the temperature. Thus an element of confusion is introduced, where the greatest accuracy is demanded. The difficulty, however, may be avoided by the use of a grating, instead of a prism, to form the spectrum.

The grating consists of a system of close, equidistant parallel lines, ruled upon glass or polished metal. If the lines are ruled upon glass, the grating acts by refraction; if upon metal, by reflection. In either case we obtain a series of spectra; the principal one of these, called the spectrum of the first order, has the great advantage that in it the relative distances apart of the various bands do not vary. Hence the grating is far better than the prism wherever exact work is needed.

The first gratings that gave really satisfactory results were those manufactured by Rutherford, of New York, about ten or twelve years ago. At present, the best of Rutherford's are surpassed by those ruled by Professor Rowland, of the Johns Hopkins University, in Baltimore. A few years ago, Professor Rowland had a very accurate ruling-machine made in Germany. By this machine nearly all the gratings now in use were made. Those gratings were found to give the best results which contained 14,700 lines to the inch. Quite recently, a new machine was constructed at the Johns Hopkins University, under the personal supervision of Professor Rowland himself. The new machine has ruled as many as 40,000 lines to the inch, and is expected to perform far better work than the old one.

With the improved gratings, there is no doubt that many discoveries will be made. Already Messrs. C. C. Hutchins and E. L. Holden, of the Harvard University Physical Laboratory, claim that their investigations, conducted by means of a large Rowland grating, render doubtful the coincidence of some Fraunhofer lines with the spectra of the metals. This, then, would seem to be the first question demanding a solution. There is also another field of investigation which will scarcely be neg lected, namely, the opinion of Lockyer about the chemical elements. He brought forward the theory that many substances now known as elements are really compound. His opinion is looked upon with disfavor by most chemists, but there are several facts which entitle it to further examination. Some of the metals, when raised to a very high temperature, give a spectrum differing from that ordinarily given by the same metals. At the high temperature, several new lines appear in the spectrum, and these new lines seem to be the same for different metals. Now there are several hydrocarbons which have a spectrum of their own when the temperature is not high enough to decompose them, and which, when heated very much, are decomposed and give the spectra of their consitutent elements. Lockyer supposed that the metals were, in the same manner, decomposed into simpler substances at very elevated temperatures, and that the new lines were due to those simpler substances. The subject certainly deserves investigation, and fortunately the investi gation is now quite possible. For the recently invented "electrical furnace," and the new method of welding by means of electricity, are said to produce a degree of heat hitherto unattained. If, then, the metals be exposed to this heat, and the new gratings of Professor Rowland be employed to analyze the light emitted, the way will be opened for discoveries of the highest importance for Chemistry and for Physical Astronomy.