remarkable property which is of such water. To an observer in remote space vital importance to us. This is the who should view the earth as a whole, problem which Dr. Stoney has attacked it is the atmospheric clouds which and of which he has offered the solution which seems to answer all the requirements. It is my object to set forth some account of this remarkable extension to our knowledge, which, even though it was made many years ago, appears to be still unknown to many to whom such matters are of interest. There is the more justification for treating of the subject at the present time, because recent researches have tended in a remarkable manner to confirm the doctrines first enunciated by Dr. Stoney. would present the most conspicuous features. They would be the objects that would command most special attention, just as from our point of view it is the clouds, perhaps of water also, which are the chief features on Jupiter, and just as the photospheric clouds are the chief features in the sun. Of course I do not for a moment suggest that the same elements which form our clouds are also the constituents of the solar clouds. The simplest consideration of the facts of the case would indeed preclude such a view. But the The analogy of the luminous cloud, illustration is of use, inasmuch as it in the sun, to the watery clouds in our suggests that as a single material sufown atmosphere, may be first referred fices to produce the characteristic terto. The vapor of water is well known restrial clouds, so a single material may to be diffused in more or less abun-suffice to produce the characteristic dance throughout the whole depth of solar clouds. the air. Under certain conditions of Let us then see if we have the necestemperature and of the quantity of sary data for ascertaining what this water present, this vapor may be con- solar material must be. We are first densed into clouds, and may thence be confronted with the fundamental quesprecipitated in rain. Under other cir- tion as to whether it is likely to be cumstances the clouds are again dis- composed of elements found on the solved into vapor according to the earth. There was a time, no doubt, ever-varying conditions of the air. when it might have been urged that The transition of water from the form in all probability the solar elements of vapor to the form of clouds is ef- were so far different from any bodies fected by a process of condensation, known to terrestrial chemists that the when the vapor, finding itself at a solar clouds must be constituted of cooler temperature than is compatible something altogether beyond our cogwith its retention of the gaseous form, nizance. But this view cannot be passes into the liquid state. Each sustained in the present state of scimolecule of the vapor thus allies itself ence. Nothing is more remarkable in with other neighboring molecules, and the recent advance of knowledge than so a little bead of water is formed and the clear demonstration of the fundathe myriads of beads thus arising con-mental unity between the elements stitute a cloud. It may be, indeed it present in the celestial bodies and probably is the fact, that the nucleus of each little droplet, around which the molecules of watery vapor cohere, is provided by some minute particle of floating matter, such as one of the motes with which the atmosphere, even when purest, is still largely tenanted. But the essential point for us to notice in our present inquiry is, that the ordinary atmospheric clouds acquire their special character from the presence of a single substance, namely, those elements of which the earth is composed. It is, no doubt, true that we have found grounds for believing that there may be one or two elements in the sun which we do not find here. We have, indeed, assigned to these dimly discerned elements the hypothetical names of coronium and helium. But even if such bodies exist at all, they are certainly wanting in the essential qualities that must be attributed to any element which purports to be the active component of the photospheric | stituent of the glowing clouds must clouds. There cannot be a reasonable possess. It must plainly be of the doubt that the sun is mainly composed most refractory or infusible nature, for of elements both well known and abundant on the earth. It is clearly among those known bodies that it is our duty to search for the characteristic photospheric material. As the terrestrial clouds consist of water, they are derived not from a simple element, but from a composite body formed of the gases, oxygen and hydrogen. The multitude of composite bodies is, of course, innumerable, and the task of searching for the solar constituent would therefore seem to be an endless one, unless we were in some way enabled to restrict the field of inquiry. This is just what the vast temperature of the sun permits us to do. It is well known that at a heat resembling that at which the photosphere is maintained, chemical compounds cannot in general exist. Ordinary chemical compounds exposed to temperatures of such elevation are instantly resolved into their elementary components. It is thus manifest that in the endeavor to find the photospheric material we have not to scan the illimitable field of chemical compounds, we have only to consider the several elementary bodies themselves. it will be noted that the photosphere only derives its capacity to radiate white light-that is to say light of every hue-from the fact that the incandescent particles from which the light is dispensed must be at least liquid, if not actually solid. No truly gaseous body could emit light possessing the properties of photospheric radiation. We thus see that whatever be the photospheric material, it must be something which is able to remain a liquid, if not indeed a solid, while at a temperature still so high that the other constituents of the solar atmosphere are retained in the form of perfect vapor. As an example of a material of which the solar clouds are certainly not composed, we may take the case of iron., This element requires, of course, a powerful furnace to transform it into a liquid, and at a still greater temperature it is known to pass from the liquid form to the gaseous form. In this gas-. eous state it is extremely abundant in the sun, as is evident from the fact that many hundreds of lines in the solar spectrum are thus accounted for. But it seems certain that the photoThus, at once, the research is nar- spheric material must be composed of rowed to a choice among some sixty-something much more infusible than. four different materials, this being iron - of something, that is, which will about the number of the different have passed into the liquid state from elementary bodies. Most of them have the gaseous state at a temperature already been actually detected in the which suffices to retain iron in a gas-, sun, and it is very likely that the others eous condition. This at once cuts iron do really exist there also in some part off from the inquiry as well as all those or other of the sun's mighty volume. elements which are more fusible than. The mere presence of an element in iron. Indeed, we may at once take the sun is, however, a very different the further step and say that no metal. thing from the presence of an element at all can fulfil the conditions that will in the photospheric clouds. There are many materials in the earth, but only one forms the clouds of our atmosphere, so there may be many materials in the sun, but only one of them may be required to give character to the photospheric clouds. be necessary. The list of possible substances receives a further reduction by the application of the important principle which Dr. Stoney was, I believe, the first to develop in his paper already referred We shall be guided in the selection to. In our endeavor to understand of the right material by the fundamen- problems of so complex a nature as tal properties which the effective con- those which the sun offers, where the conditions as to temperature and as to are animated by an average velocity pressure are so totally different from appropriate to that particular gas if it anything which we can observe around had been isolated and maintained at us on the earth or from the experi- the temperature of the mixture. Thus, ments which we can try in our labora- at the present moment the molecules tories, there is a particular advantage of oxygen and nitrogen in the air to be gained from any guidance which which we breathe being at the same the laws of dynamics can afford. These temperature, are nevertheless by no laws here come to our aid in a very means moving with the same average significant manner. They provide us, velocities. It is certain that, on the in fact, with another criterion by which whole, the molecules of nitrogen are we can sift out from the remaining list moving with a greater average speed of possible bodies that one element of than is pursued by the molecules of which it now seems certain the photo- oxygen. At the freezing temperature spheric clouds must be mainly com- we may think of the average speed of posed. the molecules of oxygen as about fifteen hundred yards per second, and of nitrogen as being a little greater. The molecular constitution that we have attributed to elements which are gaseous at ordinary temperature, may also be ascribed to the gases into which other elements are transformed when Here we must resort to that molecular doctrine of the constitution of gases which is now universally accepted. It teaches us that a gas is composed of myriads of molecules darting about, each molecule travelling quite freely except during these enormous but brief intervals when, by a collision or en- the necessary supplies of heat have counter with some other molecule, it is deflected from its path. It is an essential part of this doctrine that the average velocity with which the molecules are animated depends upon the temperature. The higher the temperature the greater the speed with which on an average each molecule hurries along. been forthcoming. The vapor of iron, no less than the vapor of water, is composed of molecules which are darting about with velocities depending for their average value both upon the temperature of the vapor and upon the mass of the molecule of iron. At the exalted temperatures which reign in the interior parts of the sun, substances even more refractory than iron must yield to the temperature to which they are exposed, and pass from the solid to the gaseous state. An object so infusible as a diamond, which of course is only crystallized carbon, would have to surrender its unrivalled hardness at the internal solar temperatures. would not, indeed, be permitted to remain in a soft or even in a fluid state, the velocities of its molecules would be such that the close association with the It For our present purpose it is essential to consider the case of two different gases at the same temperature. The velocities of the molecules are not, on the whole, equal in the two gases. It can be shown that the molecules of the gas constituted by an element with a low atomic weight will have, on the average, a higher velocity than is possessed by the molecules of a gas which, though at the same temperature, has a higher atomic weight. Thus, for instance, one gas might have molecules which were moving on the average neighboring molecules characteristic of about as swiftly as a rifle-bullet, while another gas at the same temperature but of less atomic weight would have an average speed correspondingly below that of the rifle-bullet. It is especially important to notice that in the case where different gases are mixed together, the several molecules of each the solid or the liquid state of matter would be no longer possible. The several molecules of the diamond would, in the interior of the sun, apparently roam about with the freedom enjoyed by the molecules composing any ordinary atmosphere under like conditions of pressure. The essential property of carbon, so commingled. At the same distance far as our immediate object is con- from the centre of the sun we may ascerned, consists in the fact that a mole-sume that the temperatures are equal. cule of this element, be it either in the This being so, the several molecules of solid, the liquid, or the gaseous state, the different elements in the mixture has but a small mass when compared will be moving with varied velocities, with the molecules of most other ele- corresponding on the average to their mentary bodies. We have reason to various molecular weights. Specially believe that each molecule of the same noticeable among them will be the element always has the same mass, and molecules of carbon. They are in great that different elements have in general abundance, and they are distinguished different molecular masses. It hap- from the great majority of the subpens that the mass of a molecule of stances with which they are associated carbon is much less, not only than that by the high speed at which they are of a molecule of iron, but even than generally darting along. Their motions that of a molecule of oxygen or nitro- are of course pursued in every direcgen. I do not, of course, assert that tion, myriads of molecules are flying the molecule of carbon is lighter than downwards, myriads are flying horizonthe molecule of any other element. tally, myriads are flying upwards. It That is not the case. The molecule of is these last which are at present imhydrogen, for example, is much lighter portant. than that of carbon. Indeed, the element just named has the lightest molecule of any terrestrial substance. Out encounters with the other molecules, of the sixty-four elements there are, however, only five with a less atomic weight than carbon. But what it concerns us specially to notice is that among elements which may be deemed refractory, that is to say, among elements which retain the solid or the liquid state until a temperature has been attained high enough to drive most other substances into vapor, the molecular mass of carbon is exceptionally small. We may, in fact, assert that so far as elements which are likely to exist in abundance on the sun are concerned, the case of carbon is unique. This element combines an excessively high refractory nature with an excessively low molecular mass. It will not be hard to deduce from these facts Dr. Stoney's very remarkable conclusion that carbon is the effective constituent of the clouds in the photosphere. It is, indeed, very interesting to trace out the ingenious line of reasoning by which this conclusion is established. I shall here give an outline of the argument. Picture the condition of affairs in the upper part of the solar atmosphere, where the vapors of many elements are As a molecule is flying upwards it experiences not alone all the chance That Thus but it is also directly subjected to a This consideration excludes a number of elements from possible participation in the clouds of the photosphere. Their molecular velocities are not suffi cient to maintain them at the necessary altitudes. But among the elements which are permitted to elevate themselves sufficiently, carbon now assumes a distinctly prominent position in virtue of the other remarkable property of this element to which we have re From Blackwood's Magazine. THE STORY OF MARGREDEL: BEING A FIRESIDE HISTORY OF A CHAPTER XIV. ferry at Pettycur. She sat, unheedful of her neighbors, with a hard, fixed look, such as any traveller wears in our fast day, when it is a robbery of time even to feel the wind on one's face; but it seemed so strange in a mailcoach, especially in a face so fair and young, that there were few who did not remark it. THE next forenoon saw Margrédel ferred. It is certain that the greater take her seat in the mail-coach among the distance from the solar centre, the a mixed company on its way to the lower must be the temperature to which the materials are exposed. No doubt in the interior of the sun the temperature is so high that even carbou must be there permanently gaseous. But at a sufficient altitude above the sun's surface or, to speak more accurately, at a sufficient distance from One passenger at least, the sun's centre, the temperature is with some down upon his chin, thought low enough to permit the carbon vapors to return to the liquid state and he should have liked to meet face to thus gather into the beads of liquid face with the man who caused her Doubtless the glowing carbon which forms the lumi- heaviness of heart. nous cloud. What then happens is fresh horses carried other heavy hearts clearly of the following nature. The as well as Margrédel's; but he failed high velocities of the carbon molecules are ever and anon conducting them to elevations in the solar atmosphere, where the temperature is sufficiently low to reduce the carbon vapors to the Behind the hard eyes Margrédel was cloudy state which they are so prone to assume. Herein lies the essential conning the professor's message, wondifference between carbon and the dering that he should have written it other elements. In the first place if he could come out to the street to deliver it to Rab, yet unable to think of many of the elements never possess sufficient molecular velocities to carry any cause for his sending it, save that them in any large quantities into the he required her by reason of illness. elevated regions. In the second place, From that her mind went back over among the elements which can attain many eccentricities of her uncle, and sufficient altitudes carbon is the most strange conduct of his in the past, with refractory, and therefore would be the the forebodings it bred; and all this first to take that step in condensation kept the memory of the last night's implied by its transformation into a emotions from overwhelming her, although it gave tone to her thoughts, cloud. even as the ground color of our canvas comes up through what we paint upon it. On these grounds Dr. Stoney has concluded that the same element, which is the great source of artificial light in almost all forms on this earth, is also the source of solar light. Our conception of the important functions of carbon in the universe is thus greatly extended. to observe them. Howsoever things may change in fifty years, the habit is like to last out time of young knights reading most need of a champion in pretty faces. And as not even the recuperative power of Margrédel's own land of France is stronger than that of youth and health, she was not within sight of the sea when the sunshine, and the smell of leaves from under the hedgerows, and the joy of motion, drove 1 Published under arrangement with G. P. Putnam's Sons, the authorized American publishers of the book. |