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year the negative of the Pleiades, which is well worth the trouble. The impressions of 1888, obtained with very sensitive plates and an exposure of four hours, have revealed with surprising clearness the diffuse mass of cosmical matter which envelopes this constellation, and of which the nebulæ of Maïa and of Merope are only the most luminous parts. A curious and very unexpected peculiarity is a rectilinear filament of nebulous matter which proceeds from the principal mass, over a length of 40′ of arc and a breadth of 3" to 4" only; it encoun ters on its course seven stars which it unites together as beads of a chaplet. A second line, similar but shorter, exists in the midst of the nebulous mass. This new negative contains besides twice as many stars as the first, about 2,000. The chart of the Pleiades of Mr. C. Wolf, which consumed several years of labor, contains only 671.

Mr. Pickering has entered into the same path, and very recently his plates have revealed the existence of five or six new nebulæ in different regions of the sky. Finally, some months since, Mr. Roberts communicated to the Astronomical Society in London photographs of the elliptical nebula of Andromeda, which are indeed a revelation. That which seemed an unformed mass of cosmical matter, traversed by irregular fissures, appeared now as a solar system in embryo; rings are distinguished in it, which are detached from the central mass, as is required by the hypothesis of Laplace, and two satellites in course of formation, whose relative positions must have undergone some changes since the epoch of the observations of Bond. Photography renders thus intelligible a structure which sketches are inclined to conceal.

The success obtained in this field can depend, in a certain measure, upon a particular photogenic power of nebulæ; but it is explained especially by this fact, that the sensitive plate is not dazzled by the vicinage of more brilliant objects. The nebula which surrounds the variable star Eta Argus, was invisible when this star appeared to be the first magnitude, and was discovered only when the star which eclipses it caused it to descend to the fourth order (it is now the seventh magnitude).

There is found to be an advantage of the same order in the applica tion of photography in the registering of phenomena instantaneous or of very short duration, like eclipses, occultations, meridian transits, where the cool-headed sensitive plate shields us from the trouble, and from errors inseparable from a precipitate observation. A great num. ber of total solar eclipses, also the two transits of Venus, 1874 and 1882, have already been observed by this means. The measures of numerous negatives taken by the French expeditions have been confided to a personnel of the gentler sex, under the direction of Mr. Bouquet de La Grye; they are completed, and the calculations are in a very advanced

state.

We will limit here this rapid review of the services which photography has rendered to astronomy, or which it is to render to it after a

delay which is foreseen, and which is already in some degree discounted. So great result, and so unexpected, acquired in so short a time is not this the most brilliant guaranty of the future? At the same time telescopes are perfected and attain colossal dimensions. The greatest at the present time is the refractor of 0.90m in aperture which is to be installed on the summit of Mount Hamilton, in California, where stands, 1,300 meters above the sea-level of the Pacific, an observatory founded by James Lick. This old manufacturer of organs, made rich by fortunate speculations, and desirous of perpetuating his name in the memory of men, had for a long time hesitated between a pyramid under which to be interred, and an observatory which should be erected above the clouds. It was said to him that a pyramid, which he wished to be located at the entrance of the harbor of San Francisco, would be taken in case of war for a mark by the enemy, and he decided upon the observatory, where he reposes under the great telescope. There have been spent, in constructing it and in making a road to it, more than $700,000. The bequest is not sufficient for it, and the State has been obliged to intervene. But its atmosphere has a purity unknown elsewhere; it has at least two days of fine weather out of three.

THE LIFE-WORK OF A CHEMIST.*

By Sir HENRY E. ROSCOE, F. R. S., President.

In asking myself what subject I could bring before you on the present occasion, I thought I could not do better than point out by one example what a chemist may do for mankind. And in choosing this theme for my discourse I found myself in no want of material, for amongst the various aspects of scientific activity there is surely none which, whether in its most recondite forms or in those most easily understood, have done more to benefit humanity than those which have their origin in my own special study of chemistry. I desired to show what one chemist may accomplish, a man devoted heart and soul to the investigation of nature, a type of the ideal man of science-whose example may stimulate even the feeblest amongst us to walk in his footsteps if only for a short distance, whose life is a consistent endeavor to seek after truth if haply he may find it, whose watchwords are simplic. ity, faithfulness, and industry, and whose sole ambition is to succeed in widening the pathway of knowledge so that following generations of wayfarers may find their journeys lightened and their dangers lessened.

Such men are not uncommon amongst the ranks of distinguished chemists. I might have chosen as an example the life and labors of your some time townsman, Joseph Priestley, had not this theme been already treated by Professor Huxley, in a manner I can not approach, on the occasion of the inauguration of the statute which stands hard by. To-day however I will select another name, that of a man still living, the great French chemist, Pasteur.

As a chemist Pasteur began life, as a chemist he is ending it. For although, as I shall hope to point out, his most important researches have entered upon fields hitherto tilled with but scanty success by the biologist, yet in his hands, by the application of chemical methods, they have yielded a most bountiful harvest of new facts of essential service to the well-being and progress of the human race.

And after all, the first and obvious endeavor of every cultivator of science ought to be to render service of this kind. For although it is

An address delivered to the members of the Birmingham and Midland Institute, in the Town Hall, Birmingham, on October 7, 1889. (Nature, October 10, 1889, vol XL, pp. 578-583.)

foolish and short-sighted to decry the pursuit of any form of scientific study because it may be as yet far removed from practical application to the wants of man, and although such studies may be of great value as an incentive to intellectual activity, yet the statement is so evident as to almost amount to a truism, that discoveries which give us the power of rescuing a population from starvation, or which tend to diminish the ills that flesh, whether of man or beast, is heir to, must deservedly attract more attention and create a more general interest than others having so far no direct bearing on the welfare of the race. "There is no greater charm," says Pasteur himself, "for the investigator than to make new discoveries, but his pleasure is more than doubled when he sees that they find direct application in practical life." To make discoveries capable of such an application has been the good fortune-by which I mean the just reward—of Pasteur. How he made them is the lesson which I desire this evening to teach. I wish to show that these discoveries, culminating as the latest and perhaps the most remarkable of all, in that of a cure for the dreaded and most fearful of all fearful maladies, hydrophobia, have not been, in the words of Priestley, "lucky hap-hazardings," but the outcome of patient and long continued investigation. This latest result is, as I shall prove to you, not an isolated case of a happy chance, but simply the last link in a long chain of discoveries, each one of which has followed the other in logical sequence, each one bound to the other by ties which exhibit the lifework of the discoverer as one consequent whole. In order however to understand the end we must begin at the beginning, and ask ourselves what was the nature of the training of hand, eye, and brain, which enabled Pasteur to wrest from nature secret processes of disease the discovery of which had hitherto baffled all the efforts of biologists? What was the power by virtue of which he succeeded when all others had failed; how was he able to trace the causes and point out remedies for the hitherto unaccountable changes and sicknesses which beer and wine undergo? What means did he adopt to cure the fatal silk-worm disease, the existence of which in the south of France in one year cost that country more than 100,000,000 of francs? Or how did he arrive at a method for exterminating a plague known as fowl cholera, or that of the deadly cattle disease, anthrax, or splenic fever, which has killed millions of cattle, and is the fatal woolsorters' disease in man? And last, but not least, how did he gain an insight into the workings of that most mysterious of all poisons, the virus of hydrophobia?

To do more than point out the spirit which has guided Pasteur in all his work, and to give an idea of the nature of that work in a few examples, I can not attempt, in the time at my disposal. Of the magnitude and far-reaching character of that work we may form a notion, when we remember that it is to Pasteur that we owe the foundation of the science of bacteriology, a science treating of the ways and means of those minute organisms called microbes, upon whose behavior the very

life, not only of the animal, but perhaps also of the vegetable world depends, a science which bids fair to revolutionize both the theory and practice of medicine, a science which has already, in the hands of Sir Joseph Lister, given rise to a new and beneficent application in the discovery of antiseptic surgery.

The whole secret of Pasteur's success may be summed up in a few words. It consisted in the application of the exact methods of physical and chemical research, to problems which had hitherto been at tacked by other less precise and less systematic methods. His early researches were of a purely chemical nature. It is now nearly forty years ago since he published his first investigation. But this pointed out the character of the man and indicated the lines upon which all his subsequent work was laid.

Of all the marvellous and far-reaching discoveries of modern chemistry perhaps the most interesting and important is that of the exist ence of compounds which while possessing an identical composition (that is, made up of the same elements in the same proportions), are absolutely different substances judged of by their properties. The first instance made known to us of such isomeric bodies, as they are termed by the chemist, was that pointed out by the great Swedish chemist, Berzelius. He showed that the tartaric acid of wine-lees possesses precisely the same composition as a rare acid having quite different properties and occasionally found in the tartar deposited from wine grown in certain districts in the Vosges. Berzelius simply noted this singular fact, but did not attempt to explain it. Later on, Biot observed that not only do these two acids differ in their chemical behavior, but likewise in their physical properties, inasmuch as the one (the common acid) possessed the power of deviating the plane of a polarized ray of light to the right, whereas the rare acid has no such rotatory power. It was reserved however for Pasteur to give the explanation of this singular and at that time unique phenomenon, for he proved that the optically inactive acid is made up of two compounds, each possessing the same composition but differing in optical properties. The one turned out to be the ordinary dextro-rotatory tartaric acid; the other a new acid. which rotates the plane of polarization to the left to an equal degree. As indicating the germ of his subsequent researches, it is interesting here to note that Pasteur proved that these two acids can be separated from one another by a process of fermentation, started by a mere trace of a special form of mold. The common acid is thus first decomposed, so that if the process be carried on for a certain time only the rarer lævo-rotatory acid remains.

Investigations on the connection between crystalline form, chemical composition, and optical properties occupied Pasteur for the next seven years, and their results-which seem simple enough when viewed from the vantage ground of accomplished fact-were attainable solely by dint of self-sacrificing labors such as only perhaps those who have

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