tained till now. William I. willingly accepted the protectorate, and his example has been followed by his

successors.

The Secretary Van der Aa, who had been the soul of the Society from 1751 to 1794, was succeeded by the renowned Physical Professor Martinus van Marum, who at his death in 1837 was succeeded by the Professor of Geology, T. G. S. van Breda, who took his dismissal in 1864, when the Professor of Chemistry, E. H. von Baumhauer, was appointed to the office.

From 1754 to 1793 the Society published thirty volumes of Transactions, of which registers by the celebrated T. T. Martinet were issued in 1773 and 1793. These Transactions contain essays on all branches of science, and also many on theology. It was principally through the influence of Van Marum that since then a more predominating share has been taken by physical subjects. From 1799 to 1844 a first series of 24 volumes in octavo, and from 1841 to 1866 a second series of 25 volumes in quarto, and since 1870 a third series of "Physical Transactions" have been published by the Society. In 1802 a volume in octavo of "Mechanical and Mathematical Transactions" was published, and in 1821 and 1822 two volumes in octavo of "Philosophical Transactions." From 1815 to 1820three volumes in octavo on literary and archæological subjects, and since 1851 2 volumes of "Historical and Literary Transactions" in quarto have been published. The second and third series of "Physical Transactions" are especially distinguished by the memoirs written by the most eminent men in Europe, mostly illustrated by excellent plates.

The revenue of the Society is derived from the interest of capital, for which it is indebted to the kindness of the directors and from the annual subscriptions of the actual directors. It receives no pecuniary assistance whatever from the Government.

With these means the Society endeavours to make known to the world excellent writings on physical subjects, which otherwise would be published with difficulty on account of their special character and the costliness of the illustrations.

Besides supporting such works, the Society encourages scientific researches, and since 1866 has published a journal in the French language, edited by the Secretary, under the title of "Archives Néerlandaises des Sciences Exactes et Naturelles," of which already 7 volumes have appeared. This journal is destined to make known to the world all that is produced in the Netherlands and the Dutch possessions related to physical science. This is of great service to the Dutch scientific men, since their researches, being for the most part written in a language so little known generally as the Dutch, would otherwise obtain only a very partial publicity.

The Society is composed of an indefinite number of directors, for the greater part gentlemen of wealth and social importance, who pay an annual contribution of fifty gulden (about four guineas) and manage the finances, which, however, now are especially under the charge of five directors living in Harlem, presided over by the president. There are also sixty native and sixty foreign members, who are chosen in the General Assembly, held on the third Saturday of May, from a list of candidates made by the directors and members. These members pay no contribution whatever, and receive free all the publications of the Society. This membership of the oldest and most important Dutch society is esteemed a great distinction by learned men. The English members are Davidson, Davis, Kirkman, Hooker, Lyell, Owen, Sorby, Tyndall, and Wheatstone. The president of the Society is chosen every three years by the directors. At the present time the office is filled by Baron F. W. van Styrum. When a vacancy occurs in the secretaryship, the native members nominate six from amongst themselves from whom the secretary is chosen by the

directors. He also acts as treasurer and librarian, and is the only paid officer, living in Harlem in the magnificent building belonging to the Society.

The Society exchanges its publications with almost all the foreign academies and learned institutions, and to facilitate the interchange of books, the Secretary has instituted a central bureau in imitation of the American Smithsonian Institute.

As already named, the Society has regularly published a list of prize questions, the meritorious answering of which is rewarded by a gold medal of the value of about twelve guineas, to which may be added an equal sum or more, in money. At the present time no less than twenty such medals and prizes are offered for an equal number of subjects.

At the centennial festival in 1852 the Society offered a prize of 1000 gulden for the most important work in one of the branches of physics, which should be published during the next four years, and a second of 2,000 gulden for the best in four following years. In the General Assembly of 1857 it was decided that this latter prize should not be bestowed upon anyone, but that M. Foucault should be informed that the Society regretted that his communicated discoveries had not happened in the specified time, but would bestow on him the gold medal as a proof of the high value placed on his researches. On the contrary, the first prize was doubled, on account of the difficulty of deciding between two authors of transmitted works, M. A. Decandolle of Geneva, and Herr O. Heer of Zurich, who were both judged to be deserving of the 1,000 gulden offered to each.

In the general assembly of 1869 the Society resolved. that quite independently of the medals bestowed on crowned prize questions, two new medals should be established, of the intrinsic value of 500 gulden (about 40 guineas), one to bear the name and image of Huygens, and the other those of Boerhaave. These medals will be bestowed alternately every two years on learned men in the country or abroad, who shall be thought by the Society to have made themselves particularly meritorious during the last twenty years in a fixed subdivision of the mathematical and physical sciences, by their researches, discoveries, or inventions. The Huygens medal was to be assigned in 1870 to the branch of physics, and will be assigned in 1874 to chemistry, in 1878 to astronomy, in 1882 to meteorology, and in 1886 to pure and applied mathematics.

The Boerhaave medal was to be assigned in 1872 to geology and mineralogy, and will be assigned in 1878 to botany, in 1880 to zoology, in 1884 to physiology, and in 1888 to anthropology; after which the same order will be repeated over and over again in the case of both medals, so that one medal will be given every twenty years for each of ten different subjects. The judgment is to take place by a Commission to be appointed by the directors, of which Commission the Secretary of the Society is always to be a member. The award is to be made in the General Assembly, in accordance with the pre-advice of the Commission, accompanied with a particular account of the motives which have led to the choice.

The first Huygens medal was awarded in 1870 to Rodolph Julius Emmanuel Clausius, Professor at the University of Bonn, as founder of the mechanical theory of heat; and in 1872 the first Boerhaave medal was given to Henry Clifton Sorby of Sheffield, for having made himself particularly meritorious by his microscopical researches in connection with geology and mineralogy, during the last twenty years.

The portrait of Huygens was taken from a copper-plate engraving by Edelink, and that of Boerhaave, from an oil painting by Troost, now in the Academy at Leiden. Independent of their size (3 in. in diameter, 9 oz. troy) both these medals are most creditable to all parties concerned as fine works of art.

the red, marked C, which is absolutely coincident with a prominent dark line in the solar spectrum. Now this is a black line which, by repeated observations, we know corresponds in degree of refrangibility exactly with one of the lines given out by glowing hydrogen, when examined in one of these tubes with the electric spark. When, therefore, we get any substance around the sun reporting its light to us, it is perfectly obvious, I think, that if the bright line really be coincident with this dark line, that something is probably hydrogen. This was one of the first lines determined by M. Janssen in the eclipse of 1868. There is another bright line absolutely coincident with a dark line known to correspond in refrangibility with another line given out by

hydrogen in the green part of the spectrum, marked F in the figure. This, then, is further proof in favour of hydrogen; and now notice a great difference between the shape of this line and the red line which I drew your attention to just now. An enlarged representation of this line is shown in Fig. 42.

You will bear in mind what I told you about the effect of pressure in altering the spectrum of hydrogen, and that one of the most obvious effects of increased pressure was to increase the thickness of what is called the F line-the line now under consideration, you will see here that the widening of the F line, the green line of hydrogen, really indicates a thickening due to pressure. In that way we have been able to determine approximately the pres

sure of these circum-solar regions which the spectroscope has determined to be occupied by an envelope of hydrogen gas, mingled sometimes with other vapours, which envelope I have termed the chromosphere. When the pressure of the chromosphere is completely determined, we shall be probably enabled to determine the temperature of the sun.

A line again in the violet corresponds with a dark line in the solar spectrum, which is coincident with a third line of glowing hydrogen which we have before spoken about, and there is still another coincident line. A line in the yellow of the spectrum will also be noticed. This is one which has caused a great deal of discussion, for it is not coincident with any line of any known terrestrial substance. A number of short lines are also shown in the engraving which will be seen to correspond to the part of the chromosphere which is denser, for then the F line of hydrogen has become broad where these lines are seen; these lines show that in the layers of the chromosphere nearest to the sun a number of other substances exist, amongst which may be mentioned magnesium, iron, and sodium. The reason that bodies do not reach up so far from the body of the sun is that their vapours are very much heavier than the gas hydrogen, which is the lightest terrestrial substance known. Such are a few of the practical applications of the spectroscope as applied to the radiation of light. There are other classes of facts relating to the absorption of light, on the consideration of which we shall now enter.

The subject with which we have just been dealing is the radiation or giving out of light by bodies in different states-that is to say, by solid or liquid bodies, We have now to deal with or gaseous or vaporous ones. the action of the prism upon light under some new conditions-conditions which I purposely withheld from you in the last lecture. Light is not only given out, or radiated, but it may be stopped or absorbed in its passage from the light-source to our eye, if we interpose in the path of the beam certain more or less perfectly transparent substances, be they solids, liquids, gases, or vapours. I will recall one or two of the experiments which have been already described in order that you

may see exactly how the perfectly distinct classes of phenomena due to radiation and absorption really run together. You will recollect that I pointed out to you that radiation, or the giving out of light, might be continuous or might be selective, and I am anxious now to show you that radiation is exactly equalled by absorption in this matter; that absorption may also be continuous or selective. We have before taken as an instance of continuous radiation a continuous spectrum obtained by using the electric lamp or a lime-light; that is to say, an example of the general radiation which you get from an incandescent solid-the carbon points of which the poles

FIG. 44.-Method of observing the absorption of a vapour. of the lamp are composed, or the solid lime. You will remember that if we take the spectrum of a vapour-as, for instance, that of strontium or thallium-we find that the continuous spectrum is altogether changed, and that in the place of that beautiful rainbow band, continuous from the red end of the spectrum to the violet, we really only get lines here and there, which are due to the selective radiation, and opposed to the general radiation which we spoke of in the continuous spectrum just now. I might have chosen other substances besides strontium. and thallium, but I mentioned the spectra of these substances when we were considering the question of radia

tion. What I have to dwell on now is, that the absorption or sifting of light by different bodies is very like radiation in its results-that is to say, in some cases we have an absorption which deals equally with every part of the spectrum, and in other cases we have absorption which only picks out a particular part of the spectrum here and there to act upon. But there is one important point to be borne in mind; when dealing with absorption we must always have a continuous spectrum to act upon. If we had a discontinuous spectrum to act upon, the thing would not be at all so clear. Having this continuous spectrum, the problem is, what the action of the different substances on the light will be. Let me give you an instance of general absorption. If we take the continuous spectrum above referred to, and interpose a piece of smoked glass, or better, a piece of neutral-tint glass, you will find that the substance will cut off the light and deaden the spectrum, so to speak, throughout its whole length. This neutral-tinted glass, then, has the faculty evidently of keeping back the light, red, yellow, blue, green, violet, and so on; and is an instance of general absorption. A very dense vapour would furnish us with another similar instance. Now, instead of using the neutral-tint glass, we will introduce a piece of coloured glass, the action of which, instead of being general throughout the spectrum, will be limited to a particular part of it. I have now interposed a piece of red glass, which cuts off nearly all the light except the red; and now I interpose a piece of blue glass, which cuts off everything except the extreme violet. By introducing both these pieces in the beam, the spectrum is entirely obliterated.

In these latter cases we have instances, not of general, but of selective absorption, one substance cutting off everything but the red, and the other cutting off everything but the violet. Now the fact that we can absorb any definite part of the spectrum by properly tinted glasses provides us with a practical application of spectrum analysis in the manufacture of the coloured glass used for lighthouses or signals. Further, if astronomers could find a glass of a certain red, or a glass of a certain green colour, we should be able to see the solar prominences every day without a spectroscope.

FIG. 45.-Absorption spectra of iodine and nitrous fumes.

The first practical application which springs out of these phenomena of absorption is this, that as different substances are known by the effects which they produce on radiation, so also chemists find it perfectly easy to detect different substances by means of their absorption; for instance, the absorption spectrum of nitrous fumes can be shown by taking first our continuous spectrum, which we must always have to start with, and introducing some nitric peroxide between the source of light

and the prism. The nitric oxide, immediately it comes in contact with the air, produces dense red fumes, and numbers of fine black lines will be seen immediately crossing the spectrum at right angles to its length, and to a certain extent resembling the solar spectrum with its Fraunhofer lines. Iodine is another substance which gives a coloured vapour, the absorption spectrum of which is very definite and well defined. Fig. 45, Spectrum No. 1, shows the absorption spectrum of iodine vapour, and No. 2 that of nitrous fumes. We are not limited to these substances; we will try something else-blood, for instance, about which I shall have something more to say presently. We shall find that the action of blood upon the light is perfectly distinct from the action of those fumes which we have spoken of; and instead of having typical lines in the green and blue parts of the spectrum, we have two very obvious lines in the more luminous part of the spectrum. The colour of a solution of blood is not unlike the colour of a solution of magenta; but if, instead of using a solution of blood, we use a solution of magenta, we should have only a single black band. The absorption spectrum of potassic permanganate solution is another beautiful instance. We have here something totally unlike anything we had before. Instead of the two dark bands which we saw in the case of the blood, or the single band in the case of magenta, we have four very definite absorption bands in the green part of the spectrum. So that you see the means of research spectrum analysis affords as far as regards radiation, is entirely reproduced in the case of absorption, and it is perfectly easy, by means of the absorption of different vapours and different substances held in solution, to determine not only what the absorbers really are, but to determine the presence of an extremely small quantity. Further, by allowing the light to pass through a greater thickness of the absorbing substance, the absorption lines are thickened and new regions of absorption are observed. This fact was discovered by Dr. Gladstone, who used hollow prisms containing the substance.

(To be continued.)

J. N. LOCKYER

PROFESSOR ZOLLNER ON THE CONNECTION BETWEEN COMETS AND METEORS

PROFI

ROFESSOR F. ZÖLLNER alludes in the commencement of his paper read before the members of the "Kön. Sächs., Gesellschaft der Wissenschaften" to the epoch which Schiaparelli's discovery of the concordance of the orbits of some small comets with those of periodically returning showers of shooting stars has made in the astronomical world. He quotes an instance in proof of this, namely, Biela's Comet. On November 27, last year, the earth was crossing the exact spot in her orbit, which had been cut by Biela's Comet two and a half months before. Observers aware of the coming event were on the alert with their instruments, but no good results were obtained owing to the unfavourableness of the weather.

From these facts, he says, we must naturally conclude that the physical constitution of these bodies is the same, and we are strengthened in our conclusions by Schia parelli's discovery of the identity of the envelopes and tails of comets with clouds of meteors seen by reflected sunlight, the separate elements of which only become visible at a shorter distance.

Observations, however, with the spectroscope, contradict this assumption; the light given out by comets. is found not to correspond with that of the sun; it is a light peculiar to them, like that of a glowing gas.

Further on he quotes Schiaparelli's own words to some length, with respect to the attraction exercised by other bodies on the matter composing the nuclei of comets,

which is drawn from them in directions other than that of their orbits. Schiaparelli maintains most distinctly that the tails of comets and meteoric aggregates are not identical.

Professor Zöllner points out that if we are not to suppose that the physical constitution of both phenomena is the same, there only remains their identity of origin as an explanation of the remarkable coincidence of these bodies in space. Pursuing this argument and accepting its veracity, there is.no reason to disbelieve the materials of which they are formed, to be the same. Schiaparelli supposes the nuclei of comets to consist of a solid sub. stance, which being subject to a kind of "weathering process," finally becomes broken up into separate pieces, which are turned into a meteoric swarm by the attraction and atmospheric resistance of a large planet. To this effect he again quotes Schiaparelli. Further on he expresses it as his opinion that comets and meteorites are the remains of planets, the former being their fluid and the latter their solid constituents. It must be left to future observers to decide whether the apparent disappearance of Biela's comet has any connection with the rich fall of stars observed on November 27, last year.

It is possible that the vapour left in consequence of the gradual evaporation of a comet would condense, in the absence of any powerful centre of attraction, into a number of separate centres, as a cloud is dissolved into raindrops on the increase of cold. In this way the condensed portions of cometary vapour would present the phenomenon of numerous shooting stars as they penetrate the earth's atmosphere in a solid or perhaps still fluid condition.

trace of the experiment to which it has been submitted. M. Plateau repeated the experiment upon many individuals and for various lengths of time, for the purpose of discovering, in the case of each species, the limit of time beyond which immersion caused the death of the insect. He arrived at two curious conclusions, supported by a great number of trials :

1. The terrestrial Coleoptera recovered from complete submersion continued for a very long time, in several cases for 96 hours. 2. The aquatic swimming Coleoptera and Hemiptera, far from presenting a greater resistance to asphyxia by submersion than the terrestrial insects, in most cases succumbed very much sooner.

The cause of this unexpected inferiority in the case of the aquatic insects M. Plateau thinks is due exclusively to their greater activity in the water, causing as a consequence a more rapid loss of oxygen.

II. Influence of Cold: Effects of Freezing.

The results of M. Plateau's experiments in this direction are that the aquatic Articulata of the latitudes of Belgium exist for an indefinite period in water maintained at zero (centigrade) by means of melting ice; while they cannot remain alive in ice for any length of time-not for half an hour at the utmost. The latter phenomenon appears to be accounted for by the fact that the insects are completely deprived of all power of motion, thereby losing completely their animal heat. III. Action of Heat.

Under this head M. Plateau tries to show the maximum temperature of water in which fresh-water Arachnoids can live. He finds that the highest temperature they can endure without injury oscillates between 33°5 and 46°2 centigrade. Comparing these results with those which have been obtained by experimenting with animals be

The swimming aquatic Articulata which breathe air come frequently to the surface to renew their supply. The questions, How long may they with impunity remain submerged? what is their power of resisting asphyxia, as compared with that of terrestrial insects? are answered by the following experiments. At the bottom of an open vessel, of one litre capacity, full of ordinary fresh water, is placed a very small vessel, containing about 200 cubic centimetres. A piece of cotton netting so covers the mouth of the latter, that an insect, placed in the small vessel, is in reality in the general mass of the water, but cannot ascend to the surface. Terrestrial insects placed in these conditions, impelled by their specific lightness, rise to the lower surface of the network; the movements of their legs soon cease, they do not appear to suffer, and they quickly grow torpid. The Coleoptera and aquatic Hemiptera, on the contrary, instead of submitting passively to their fate, endeavour to quit their prison, swim rapidly about, exert themselves to come to the surface, and keep struggling until their strength is enfeebled, and end by lying at the bottom as if dead.

In order to recover from its state of general torpidity an insect which has been submitted to prolonged immer. sion, it is necessary, after having taken it out of the water, to place it upon absorbing paper. If the time of its immersion has not passed a certain limit, the animal gradually recovers its energy, retaining no sensible By M. Felix Plateau.

temperature which aquatic vertebrata, articulata, and molluscs can support probably does not exceed 46° centigrade.

NOTES

WE have received a communication from Dr. Rein, Director of the Lenckenberg Society of Naturalists at Frankfort, which amusingly illustrates the perils that accompany the honours of the translation into a foreign language of a scientific work. Our informant relates that the well-known publisher, M. R. Oppenheim, of Berlin, having recently obtained the sanction of Mr. Poulett Scrope for the publication of a German translation of his work on "Volcanoes," of which a new issue lately appeared in this country, confided the work of translation to Prof. G. A. von Klöden, who accordingly performed the task. The translation was printed, together with a preface written by M. von Klöden himself—which preface, in the hurry of business, and in reliance, of course, on the good faith of the translator, the publisher forebore from examining. The volume in due course appeared, and was circulated by the publisher; and not till then was it discovered that the preface aforesaid consisted of a severe and indeed bitter critique of the work to which it was prefixed, and of the author's views as therein stated of the theory of volcanic energy, and its external development in the formation of cones and craters, &c. The explanation is that Prof. von Klöden happens-unluckily for the author whose work he undertook to translate-to have been all his life an earnest advocate and teacher of the famous "Erhebungs-Krater," or upheaval crater" theory of Humboldt and Von Buch, which Mr. Scrope, together with Sir C. Lyell, Constant Prevost, and other geologists have persistently opposed, and are, we believe, generally considered to have satisfactorily refuted. Of course it is open to Prof. von. Klöden to expound and defend his own opinion on this subject to the fullest extent in any independent publication; but it does seem to be stretching the liberty of free expression on

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