the psychologist. The Heidelberg Professors received a letter from a worthy farmer in Silesia thanking them for the great discovery they had made; it had particularly interested him, as it confirmed in a remarkable manner a theory which he had himself long held respecting the nutrition of plants; he believed that all artificial addition of inorganic materials to the plants in the shape of manure, was quite unnecessary, as the plants obtained the alkalies, the phosphorus, and the silica, &c., which they require, if a sufficient supply be not present in the soil, from the sunlight! The Heidelberg Professors, he continues, had clearly proved the presence of sodium, potassium, iron, and magnesium (all substances needed by plants), in the sunlight, and he felt sure that his theory of vegetable nutrition now required no further proof, but must at once be adopted by the previously incredulous world.

As a similar instance of this unconscious perversion of facts, we may mention the case of an English gentleman who believed that by a series of elaborate experiments he had proved the presence of iron in the sunlight! In spite of the previous caution of an eminent man of science, this gentleman was induced to publish his views, because, as he says, 'the whole scope and object of Bunsen's and Kirchhoff's experiments are to prove 'the possibility of the most minute particles of metal existing in light, and the probability of certain dark lines in the solar 'spectrum being formed by iron!' Thus, the fact of the existence of iron in the body of the sun, at a distance of 95,000,000 miles, is represented by these scientific fanatics-we really can use no milder term as being identical with the existence of iron in the sunlight, which, travelling at the rate of 192,000 miles per second, bathes the whole universe in its vivifying beams.

Of stellar chemistry applied to other self-luminous celestial bodies, we have at present but little knowledge. Fraunhofer, as we have already stated, observed that the spectra of the fixed stars contained dark lines differing from those seen in the solar spectrum. The half-century which has elapsed since Fraunhofer made these observations has not brought us further knowledge on this point, although it has assured us of the truth of his statements. In the spectrum of Sirius he observed no dark lines in the orange-coloured region; but in the green there was a distinct line, and in the blue two dark bands, none of which were seen in solar light. The spectra of other stars were likewise examined by Fraunhofer, and they appeared each to differ from the other. The difficulties attending the exact observation and measurement of the dark lines in the spectra of the stars are, of course, very

great but, with the aid of the vastly improved optical instruments of the present day, we believe that astronomers will overcome these difficulties; and we look forward with interest to no far distant time, when we shall receive some clue to the cause of the colour of those wonderful blue and red stars which appear to be confined to certain quarters of the heavens.*

In the last chapter of Professor Kirchhoff's memoir he leaves the sure road of inductive reasoning, and puts forward a theory on the physical condition of the sun. Doubtless the Professor is as well aware as any one can be of the great dif ference between his discovery of the existence of the metals in the sun and his physical theory of the solar constitution. One is an ascertained fact, the other is a mere hypothesis. It is, however, necessary to point out this difference, lest many who may not agree with the theory of the physical constitution of the sun proposed by Kirchhoff should think themselves at liberty to discard his discovery of the presence of the metals in the solar atmosphere. It is not possible to give here the arguments which may be adduced in favour of, or in opposition to, Professor Kirchhoff's theory. Scarcely, indeed, can we do more than quote one or two passages from his memoir, to give an idea of his views respecting the structure of the sun :

'In order to explain,' he says, 'the occurrence of the dark lines in the solar spectrum, we must assume that the solar atmosphere encloses a luminous nucleus, producing a continuous spectrum, the brightness of which exceeds a certain limit. The most probable supposition which can be made respecting the sun's constitution is, that it consists of a solid or liquid nucleus, heated to a temperature of the brightest whiteness, surrounded by an atmosphere of somewhat lower temperature. This supposition is in accordance with Laplace's celebrated nebular theory respecting the formation of our planetary system. If the matter, now concentrated in the several heavenly bodies, existed in former times as an extended and continuous mass of vapour, by the contraction of which sun, planets, and moons have been formed, all these bodies must necessarily possess mainly the same constitution. Geology teaches us that the earth once existed in a state of fusion; and we are compelled to admit that the same state of things has occurred in the other members of our solar system. The amount of cooling which the various heavenly bodies have undergone, in

We rejoice to see, from his last annual report, that the Astronomer-Royal is about to undertake the examination of the spectra of the fixed stars. He remarks-'I have prepared a prism-apparatus to be used in conjunction with the SE. Equatorial for the examination of the fixed stars; but hitherto I have been able to do little more than adjust its parts.'

accordance with the laws of radiation of heat, differs greatly, owing mainly to the difference in their masses. Thus, whilst the moon has become cooler than the earth, the temperature of the surface of the sun has not yet sunk below a white heat.

'Our terrestrial atmosphere, in which now so few elements are found, must have possessed, when the earth was in a state of fusion, a much more complicated composition, as it then contained all those substances which are volatile at a white heat. The solar atmosphere at this present time possesses a similar constitution. The idea that the sun is an incandescent body is so old, that we find it spoken of by the Greek philosophers. When the solar spots were first discovered, Galileo described them as being clouds floating in the gaseous atmosphere of the sun, appearing to us as dark spots on the bright body of the luminary. He says, that if the earth were a self-luminous body, and viewed at a distance, it would present the same phenomena as we see in the sun. (Kirchhoff. Researches, &c., p. 24.)

Certain appearances connected with those spots on the sun's surface have induced astronomers in general to adopt a different theory of the constitution of the sun from that proposed by Galileo and supported by Kirchhoff. This theory supposes, according to Sir William Herschel, that the centre of the spot reveals a portion of the dark surface of the sun, seen through two overlying openings- one formed in a photosphere, or luminous atmosphere, surrounding the dark solid nucleus, and the other in a lower, opaque, or reflecting atmosphere. The supposition of the existence of such an intensely ignited photosphere surrounding a cold nucleus is, according to Kirchhoff, a physical absurdity. He puts forward his views on this point clearly and forcibly in the following passage:

'The hypothesis concerning the constitution of the sun which has been thus put forward in order to explain the phenomena of the sunspots, appears to me to stand in such direct opposition to certain well-established physical laws, that, in my opinion, it is not tenable, even supposing that we were unable to give any other explanation of the sun-spots. This supposed photosphere must, if it exists, radiate heat towards the sun's body as well as from it. Every particle of the upper layer of the lower or opaque atmosphere will therefore be heated to a temperature at least as high as that to which it would be raised if placed on the earth, exposed to the sun's rays, in the focus of a circular mirror whose surface, seen from the focus, is larger than a hemisphere. The less transparent the atmosphere is, the quicker will this temperature be attained, and the smaller will be the distance to which the direct radiation of the photosphere will penetrate into the mass of the atmosphere. What degree soever of opacity the atmosphere may possess, it is certain that in time the heat will be transmitted, partly by radiation, partly by conduction and convection, throughout the whole mass; and if the atmosphere ever had

been cold, it is clear that in the course of ages it must have become intensely heated. This atmosphere must act on the nucleus in the same way as the photosphere acts upon it; the nucleus must likewise become heated to the point of incandescence. It must therefore give off light and heat; for all bodies begin to glow at the same temperature.' (Kirchhoff. Researches, &c., pp. 25, 26.)

Our author then proceeds to account for the phenomena of the solar spots by the supposition of two superimposed layers of clouds being formed in the solar atmosphere. One of these, being dense and near the sun's surface, does not allow the light of the underlying portion of the sun to pass, and forms the nucleus of the spot; whilst the other, being produced at a higher elevation, is less dense, and forms what we term the penumbra.

It is unfortunate for Kirchhoff's theory that the unanimous verdict of all who have examined these singular phenomena is in favour of their being funnel-shaped depressions. Preconceived notions have, however, so powerful an influence over the mind, and it is so difficult to obtain a truthful estimate of relative depression and elevation at such distances, that we are willing to believe that astronomers may possibly be mistaken in their views on this subject. There is, however, one method of observation which would seem qualified to settle the disputed question. If the astronomers' view of the construction of the spots is correct, the dark nucleus never can be seen beyond the penumbra, when the spot moves round towards the sun's limb. On Kirchhoff's view such a separation of the two clouds forming nucleus and penumbra is perfectly possible, and when they have nearly reached the edge of the sun's disc, we ought to see the dark cloud below, and separate from the upper one. Such a separation, however, has not been noticed, and on the other hand we may adduce the following observation of Sir William Herschel as leading to a directly opposite conclusion: -

'Oct. 13, 1794.—The spot in the sun, I observed yesterday, is drawn so near the margin, that the elevated side of the following part of it hides all the black ground, and still leaves the cavity visible, so that the depression of the black spots and the elevation of the faculæ are equally evident.'

The more the question of the physical constitution of the sun is considered, the more does it appear that we have no right to make up our minds concerning it, either in one way or the other. Seeing how little is really known about the matter, with the true spirit of scientific inquirers, we hold ourselves open to conviction as soon as satisfactory evidence shall be brought forward. The singular observations first made by Mr. James

Nasmyth, a few months ago, concerning the physical condition of the sun's surface- observations so novel that astronomers were loth to receive them as facts until they were confirmed by other observers need only to be mentioned in order to show that we are not in a position to uphold any theory whatever of the physical constitution of our great luminary. Mr. Nasmyth asserts, and his assertion has been confirmed by the subsequent observations of more than one competent observer, that the wellknown mottled appearance which the surface of the sun exhibits. is due to the presence of willow-leaf-shaped' luminous bodies, which, interlacing as it were, cover the whole surface of the These most singular forms can be well observed, according to Mr. Nasmyth, in the bridges' or streaks of light which cross the dark spots, and they are there seen to move with an astonishing velocity. Imagination itself fails to give us the slightest clue to the probable constitution of these most recent of astronomical novelties!

sun.

The beautiful red prominences seen projecting from the sun's disk during a total solar eclipse, and reaching to a height of 40,000 miles above the sun's visible surface, are likewise objects whose existence cannot be reconciled with any of the proposed theories of the sun's structure. Thanks to Mr. De la Rue, we have attained some knowledge concerning these wonderful flames, as, by the help of photography, this gentleman has succeeded in proving that the prominences really belong to the sun, and are not caused in any way by the light passing over the interposed surface of the moon, as was by some imagined.

In considering the subject of solar chemistry, or indeed of any other novel branch of science, we cannot be too frequently reminded of the incompleteness of our knowledge. This is especially the case with reference to the subject to which we have now directed the attention of our readers. But although the results of these agencies are still very imperfect, and leave ample space for the labours of future investigators, yet the discovery of this new method of analysis is at once so original and so important, that we do not hesitate to rank it among the greatest achievements of science in this age, and we await with great curiosity its further application.

* Memoirs of the Literary and Philosophical Society of Manchester. 3rd Series, vol. i. p. 407.