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according to the time when we look at it, sometimes showing us a little more of its eastern, sometimes a little more of its western, regions. Mercury presents itself to the sun in different phases of its cycle in a similar manner. It constantly directs one of its diameters, not toward the focus of its elliptical orbit which is occupied by the sun, but toward the second focus. These two foci being distant from one another not less than a fifth of the whole diameter of the orbit of Mercury, the libration of the planet is enormous. The point that receives the rays of the sun vertically changes its place on the surface of the planet, and performs an oscillatory movement along the equator forty-seven degrees in amplitude, or through more than one eighth of the equatorial circumference. The whole duration of this oscillation, including the going and returning, is equal to the time employed by Mercury in traversing its orbit, or about eighty-eight terrestrial days. Thus Mercury stands oriented toward the sun like a magnet toward a mass of iron; but this orientation is not constant to the point of excluding a movement of oscillation of the planet to the east and to the west, like that which the moon performs toward us.

This oscillation is of great importance for the physical condition of the planet. Suppose, for instance, that it did not exist, and that Mercury always turned the same hemisphere to the light and heat of the sun, the other hemisphere remaining plunged in perpetual night. The point of the surface situated at the central pole of the illuminated hemisphere would have the sun eternally in the zenith; the other points of the planet accessible to the solar rays would have the sun always at the same point in their horizon, at the same height, without any apparent movement, without any perceptible change; consequently, no alternation of night and day, no variety of season; the stars eternally invisible because of the perpetual presence of the sun; and, Mercury having no moon, we can hardly imagine how the inhabitants of those regions, condemned to an endless day, could find a means of regularly computing time.

Such are, in fact, nearly the conditions that prevail in Mercury, but only approximately. The oscillating movement of the Mercurial globe as toward the sun would be attributed by an observer on the surface of the planet to the sun, as we attribute to the sun the diurnal movement which really appertains to the earth. To us the sun seems to circle regularly from east to west, defining in twenty-four hours the period of day and night; to the observer on Mercury, the sun will describe a back-and-forth movement through an arc of forty-seven degrees in the celestial vault, while the position of the arc as toward the horizon will always be the same. The complete period of the double oscillation will com

prise almost exactly eighty-four terrestrial days. According as the arc of solar oscillation is all above the horizon of the observer or all below it, or partly above and partly below it, there will be different appearances and a different distribution of light and heat. In the regions, covering three eighths of the planet, where the arc is all below the horizon, the sun will never be seen, and the darkness will be perpetual. Thick and eternal night will reign there, except perhaps from the accidental appearance of some light produced by refraction and atmospheric glows, or phenomena like the aurora borealis; together with the light emitted by the stars and planets.

Another part of Mercury, including also three eighths of its surface, will have the arc of oscillation all above its horizon, and will be continually exposed to the rays of the sun, without any other change than the variations in the obliquity of the rays through the different phases assumed during the period of eightyeight days. Night is absolutely impossible. In other regions, covering a quarter of the planet, in which the arc of oscillation is partly above and partly below the horizon, there will be alternations of light and darkness. In these privileged regions the period of eighty-eight days will be divided into two intervals, one characterized by a continuous light, the other by darkness; the two intervals will be equal in some places, of different length in others, according to the position of the place on the surface of the planet, and the length of the part of the solar arc which appears above the horizon.

The possibility of organic life in a planet constituted after this manner depends on the existence of an atmosphere capable of distributing heat into different regions, in such a way as to diminish the extremes of heat and cold. Schroeter, a hundred years ago, suspected the existence of an atmosphere round Mercury; my observations afford more definite indications of it, and affirm its existence with a much greater probability. The spots of the planet are most clearly visible when they are in the central parts of the disk, and grow dimmer and ultimately disappear as they approach the border. I have been able to assure myself that this phenomenon is not merely due to the greater obliquity of the perspective, but is because some obstacle is really presented to the view of spots situated in such positions. That obstacle can hardly be anything else than the greater extent of atmosphere that the light-rays have to traverse in coming from the edges than from the center of the disk. We have, therefore, reasons for believing that the atmosphere of Mercury is less transparent than that of Mars, and more nearly like that of the earth. The circular contour of the planet, moreover, in which the spots become less visible, always appears more luminous than the rest, but often irregularly

luminous, more so at some points than at others; and sometimes we can see on its borders bright white regions that remain in sight several days in succession, but are generally changeable, and show themselves sometimes in one place and sometimes in another. I attribute these phenomena to condensations going on in the atmosphere of Mercury, which reflects more light into space the more opaque it becomes. Similar white regions are also often seen in the interior of the disk, but they are not so brilliant there as on its border. Further, the dark spots of the planet, while they are permanent as to form and arrangement, are not always. equally evident. They are sometimes more intense, at other times paler. Sometimes, also, one or another of them will become momentarily invisible. Such peculiarities can not be attributed to any other cause than atmospheric condensations similar to our clouds, which veil the ground of the planet in different degrees, sometimes in one region, sometimes in another. An observer, looking from the depths of space upon the countries of our earth covered with clouds, would perceive a like spectacle.

Very little can be said of the nature of the surface of Mercury. We must recollect that three eighths of it are inaccessible to the solar rays and to sight; on that side, therefore, we have but slight hopes of ever learning anything certainly. It will also be hard to gain a correct and sure knowledge of the part we can see. The dark spots, even when they are not clouded, usually appear under the form of extremely thin trails of shadow. In ordinary conditions they are distinguishable only at the expense of much attention and weariness. Under the best conditions they have a brown, warm tint, like that of sepia; of a tone very indistinct upon the general color of the planet, which is usually of a clear rose bordering on copper. Forms or bands so vague and diffuse, with indistinct borders, always leaving a place for arbitrary definition, are not easily represented in a satisfactory manner. Still, I believe the indeterminateness of outlines is, in the majority of cases, only apparent, and a result of the insufficient optical power of the instrument; for the more perfect the view and the finer the image we get of the shadows, the more do we find them disposed to break up into a multitude of smaller details. By employing more powerful telescopes, they could doubtless be resolved into more reduced forms.

While it is so hard to make a good study of the dark spots of Mercury, it is not easy to express a well-founded opinion upon their nature. They might be attributed to the different materials composing the solid surface of the planet or to its structure, as we know is the case with the moon. But if we are disposed to consider them as in some way resembling our seas, and to suppose the existence of an atmosphere around the planet, with condensa

tions and precipitations, I do not know of any decisive arguments that can be opposed to the opinion. The spots are not gathered in large masses, but are disposed in areas and zones of small extent; are greatly ramified, and alternate with considerable uniformity with clear spaces. We may, therefore, conclude that no vast oceans or great continents exist on Mercury; but that land and sea interpenetrate one another and give rise to conditions very different from those which exist on the earth, but which may be more desirable.

Mercury is a world that differs from ours as much as Mars does. The sun lights it and warms it much more intensely than it does the earth, and in a very different way. If life exists in that world, it is doubtless under conditions so different from ours that we can hardly imagine them. The eternal presence of the sun, darting its rays almost vertically on some regions, and its perpetual absence in the opposite countries, would seem intolerable to us. And yet, if we reflect upon it, we shall remark that such a contrast would produce a more rapid, more powerful, and more regular atmospheric circulation than that which spreads the elements of life over the earth; and it possibly is brought about in this way that as complete and even perhaps more perfect equilibrium of temperature is produced on the whole planet than with us.

Mercury, by directing the same face toward the sun during its whole revolution, is peculiarly distinguished from the other planets, all of which the length of whose rotation has been determined, turn round their axes in a few hours. This mode of rotation, however, which would be unique among the planets, seems common enough among the satellites. All testimony is to the effect that our moon has always conformed to it. The first three satellites of Jupiter probably behave in the same way, and the observations of Auwers and Engelmann demonstrate that the fourth does so. Cassini verified the same fact for Japhet, the eighth satellite of Saturn. It may, therefore, be considered the rule among the satellites, while it is an exception among the planets.

The exception may probably be attributed to the proximity of Mercury to the sun, and perhaps also to the fact that it has no satellites; and depends, I think, on the way Mercury was formed when the solar system took its present shape. The peculiarity constitutes a new datum to be added to those which astronomers will have to take account of in studying solar and planetary cosmogony.-Translated for the Popular Science Monthly from a French version by F. TERBY in Ciel et Terre.

ARTIFICIAL HONEY AND MANUFACTURED SCIENCE.

BY ALLEN PRINGLE,

PRESIDENT OF THE ONTARIO BEE-KEEPERS' ASSOCIATION.

E are often told that this is a scientific age, and the state

WE ment is undoubtedly true. The world now more than ever

before looks to science as a secular if not a spiritual guide. However much their speculations may be questioned and controverted, the scientific book and the scientific man are popularly accepted as authority, at least on matters of physical and historical fact. The veracity of science therefore is, or ought to be, above suspicion. How careful, then, ought the teacher and exponent of science to be that his assertions are true; that his alleged facts are facts; and that even his speculations are free from the appearance of dogmatism! He needs to be especially particular when writing for the general public, for people untrained in science will accept his statements as expert testimony. Errors will thus be sure to mislead his readers, many of whom are without the knowledge that would enable them to discriminate between the true and the false in his assertions.

In The Popular Science Monthly for June, 1881, appeared an article on Glucose and Grape-Sugar, by Prof. H. W. Wiley. In that article the following unfortunate statement was made: "In commercial honey, which is entirely free from bee mediation, the comb is made of paraffin, and filled with pure glucose by appropriate machinery." To say that there was not one word of truth in that extraordinary assertion is the short and proper way to put it, and that is exactly what I undertake to say. There was not a tittle of evidence that any such honey had ever been made up to that time, nor is there a particle of evidence that any such honey has since been made.

Nevertheless, this vile slander on an honest and honorable industry has done incalculable injury to bee-culture in America, if not throughout the world. A lie is said to travel half round the world while the truth is getting ready to start, and this one proved no exception. Though contradicted and refuted over and over again, it still lives and is still going. Newspapers still keep iterating and reiterating Prof. Wiley's slander, but they seldom publish a correction. Thousands of people, common and uncommon, still believe that scientific yarn that comb-honey is manufactured throughout without "bee mediation," and why shouldn't they? The former believe it because the newspapers say so, and the latter because the magazines and encyclopædias say so; for it is a fact that this itinerant fiction has actually found a place in

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