direction the result of unconscious observation, and that some animals possessed the first in a pre-eminent degree? The wonderful faculty hunters possess of finding their way through immense mountainous tracts so thickly wooded that one cannot see far her han a few yards at a time, may perhaps be accounted for by this power of unconscious observation alone; but is it so easy to account for a sudden derangement of the sense of direction, and the peculiar distress it occasions, even when there is no ground for alarm on the score of safety? This appears a kind of converse of the instance Mr. Darwin gives of the case of old persons losing their way. HENRY FOrde

The Walk, Lyme Regis, April 6

Destruction of Rare Birds: White Tom Cats MANY of our birds are now protected by law, at certain seasons of the year. But unhappily rare visitants are mercilessly killed.

Last year a pair of Hoopoes frequented my grounds both in the spring and autumn. It was a great pleasure to see this bird (of which Horapollo wrote that it was worthy to be "the sceptre of the gods on account of its gratitude"), on the lawn, busily searching for insects, or alighting on the surrounding trees. Every lover of nature will sympathise with my household and myself, in our distress that they have been shot; not even for the miserable satisfaction of the mere collector, but far worse, that their plumage might be stuck on a lady's head-gear. To shoot storks, spoonbills, bee eaters, hoopoes, &c., which might be regular visitants and nest here, is a very different thing from securing chance arrivals from remote regions, which could never be naturalised in England.

One of your correspondents wrote recently of the deafness of

white Persian tom cats. I possessed such an one for years which

was not deaf; another, in a house near me, is not deaf, and I now have a grand fellow, a true Persian, in possession of all his faculties. A neighbour's pussy having walked into the house, with characteristic Oriental hospitality he went to the larder, and selecting a fish which he doubtless thought would be a bonne bouche for his guest, laid it before his friend, and did not himself partake of it.

Trebah, Cornwall, March 31

Phosphorescence in Wood

C. F.

If some one would be good enough to give me a little information concerning the following (to me novel) phenomenon, he would oblige.

A heap of sticks intended for firing, lay in a corner of our

boiler-house, and among them were some round pieces of Scotch fir (Pinus sylvestris) about 6 or 8 inches in diameter, and 18 inches long. These had been sawn from a pole which had lain out in the wet, and being consequently rather damp, the cut portions were placed in the warm boiler-house to dry. The blocks I speak of appeared quite sound. From the circumference of three or four of them the bark was rubbed off, here and there in patches, and a few chips were broken away from the edges. The fresh surface beneath was covered with a thin layer of the ordinary sticky resin, which so copiously exudes from this and other trees. When it was dark the steward happened to enter the boiler-house, and looking towards the sticks he was surprised to see a pale steady light emitted by some of them. At first he thought it was the reflection of the moon which shone through the window. Closer examination, however, proved: (1) that the moon did not shine on the sticks at all; (2) that the sticks were self-luminous; (3) that it was only the Scotch fir blocks which emitted any light; (4) that the light was confined to the resinous surface, exposed beneath the bark and chips; (5) that the surface beneath the chips (that is where more than the bark had been removed) was brightest. The steward carried the block which appeared most brilliant to an outhouse, where it still continued to "shine." He then broke off some small loose chips with his fingers from this block, and each separate chip sent forth the same steady pale light. My informant states that the phenomenon was very curious." Perhaps this species of phosphorescence may not be unusual after all; but not being well"up" in the subject, I would with your permission, sir, merely ask is it common, and if so, how is it explained in the instance I mention? I may state that the steward gave me all the information. I saw the blocks afterwards but not the curiosity. RICHARD M. BARRINGTON

Fassaroe Bray

66

Indices of Journals

PUBLISHERS of periodicals, scientific or other, issue general indices only after intervals of ten or twenty years. In the ninth or nineteenth year the investigator of bibliography has to turn over every volume, a fearful waste of time. I have consulted with the librarian of this University, and the proposal we have to make is that the publishers should send, at least to the libraries, a duplicate copy of the annual index of each journal, or better a revised proof in slips, to be cut up and pasted into a volume which would thus be annually extended for nine years, and superseded in the tenth by the general index. The addition to the expense in a library is very trifling, and a small payment for the extra copies of the indices would protect the publishers against loss. Glasgow University

JOHN YOUNG

THE DUTCH SOCIETY OF SCIENCES

THE following account of the history of the Dutch Society of Sciences at Harlem has been drawn up by the Secretary, E. H. von Baumhauer, for publication in England. It shows the progress of science in Holland, and the great interest taken in its advancement both in that country and abroad, as proved by the award of so many valuable gold medals, and by the recent establishment of a central bureau for the exchange and transmission of books; all which activity is maintained without any of the expense falling on the scientific members.

In the middle of the last century the greater part of the aristocracy of Harlem were desirous of finding recreation in physical experiments and scientific researches. Along with several regents of the town they decided in 1752 to establish a self-supporting society, for the collection of written essays, and the bestowal of prizes on those of meritorious character. At the first meeting, May 21, 1752, the preacher, C. C. H. van der Aa, was appointed secretary, and many other protectors of the sciences and learned men in other parts of the country, were invited to become members, amongst whom were Musschenbrock, Gambius, Alberti, and others, so that by the end of the year the Society was already formed of twenty-three directors and members. The design was to include all branches of science, and to search for everything necessary for the present and future prosperity of the Republic, both in its internal and external relations, in peace and in war. Even communications on theological subjects were not excluded, treated in such a manner as not to The motto of the Society offend Christians of any sect. was Deo et Patria. By the help of many wealthy persons the Society was enabled to crown several prize essays, published in the transactions. In July 1754 the protectorate was conferred on the young hereditary governor, William Prince of Orange.

Several very eminent native and foreign men became members of the Society, and the first volume of the Transactions was so favourably received that a second edition was necessary. It was also in great part translated into German. The prize questions excited much interest in other countries, so that several were answered by foreigners. Since 1772 an annual programme has been published in both Dutch and French.

After an existence of twenty-five years the Society founded a sub-division, more specially devoted to commerce, agriculture, and industry, under the name of the Commercial Branch. This was the origin of what was afterwards called the Dutch Society for the Promotion of Industry, which in 1877 will celebrate its centenary festival,

The parent institution continued in a flourishing state until 1780; but the mournful political situation of the country for some time after that had a most injurious effect, so that the very name of this Society was continually changed. From 1798 it was called the Bavarian Society. King Louis called himself perpetual President of the Royal Society of Sciences; but in 1830, by order of the Emperor's Governor, the Prince of Plaisance, the name of the Dutch was again adopted, and has been re

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 Transac tions" 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.

A

ON THE SPECTROSCOPE AND ITS
APPLICATIONS
VII.

NOTHER point was also very obvious to those who are familiar with these inquiries, namely, that if these prominences really consisted of gas, by the use of a powerful spectroscope it was perfectly unnecessary to wait for eclipses at all. The reason for this will be clear on a little consideration; if we take a continuous or unbroken spectrum and apply successively a number of prisms, the spectrum will become proportionately lengthened, and therefore more and more feeble, and in fact we can thus reduce the light to any degree required; if now, on the

other hand, we take a spectrum which consists only of bright lines, say of one line in the red and another in the blue, and as before apply successively a number of prisms, we shall, it is true, increase the length of the spectrum, that is the distance between the two lines, but this will be all; the additional prisms have no power to alter the width of the lines themselves, for we have seen that these are simply the images of the slit, Their light, therefore, will only be slightly enfeebled. owing to reflection merely. Thus if we have a mixed light to analyse, part of which comes from a source giving out a continuous spectrum, and the rest that of a glowing gas, although when working with a single prism no lines may be visible on account of the brightness of the con

tinuous spectrum, yet by using say five or seven prisms we can so dilute the continuous spectrum as to render the bright lines of the glowing gas clearly visible. The case of the red flames round the sun is a case in point. They are invisible to the naked eye and in telescopes on account of the intensely illuminated atmosphere which also pre vents anything like bright lines being observed from these red flames, until the bright continuous spectrum has beer nuch reduced, when this has been done the bright lines of the spectrum, should there be any, will appear on a

vations on the uneclipsed sun, by means of the new method I have just sketched out. The accompanying woodcut (Fig. 40) shows the spectrum which is observed from these solar prominences. The spectrum of the prominences is shown in the upper, and that of the sun in the lower half of the engraving. This method is very easy to understand if you bear in mind the engraving of the spectroscope for solar work, and recollect that when we wish to examine the regions round the sun, the light of the sun is allowed to fall on the slit in such a way that HP

FIG. 41 -C line I right in chromosphere, dark in sun. comparatively dark background. M. Janssen, who was sent out by the French Government to observe the eclipse which was visible in India in 1868, Major Tennant, and others, had no difficulty in recognizing in a moment, when the sun was eclipsed, that these things really did consist of gases or vapours, and M. Janssen, a very careful observer, had no difficulty in determining that the gas in question was really hydrogen gas. M. Janssen and myself were also enabled to determine this by obser

FIG. 47.-F liue in chromosphere, showing widening near the sun. one half of the slit at the focus of the object glass of the large telescope is occupied by the brilliant image of the sun, and the other half is fishing, so to speak, around the limb or edge of the sun, so that if there is anything at all around the limb, the spectroscope, in the-to the eye-unoccupied part outside the image, picks up this something, and gives us its light sorted out into its proper bright lines in the spectrum. This spectrum shows that there is first a bright line, Fig. 41, in

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 Fin 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. line is shown in Fig. 42. An enlarged representation of this

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, or gaseous or vaporous ones. We have now to deal with 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

FIG 45-Absorption spectra of iodine and nitrous fumes.

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.

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

PROFESSOR F. ZÖLLNER alludes in the com

mencement 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 Schiaparelli'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,