If in any planet we could detect the traces of vegetable life it would at once be a strong argument for the existence of animals there and vice versa.

Henry Draper.

Schiaparelli points out that "the polar snows of Mars prove in an incontrovertible manner that the planet, like the Earth, is surrounded by an atmosphere capable of transporting vapor from one place to another." Mr. E.E. Barnard, in the "Astrophysical Journal," Volume XVII, No. 4, in speaking of the polar caps, says: "There seems no definite proof that they are not as much ice and snow as that which we have to deal with in our own terrestrial winters. So much is at least suggested by the great seasonal changes they undergo from winter to summer. There seems to be a general belief now that Mars certainly has an atmosphere. This atmosphere seems to be very much less than our own, and yet it is of sufficient density to produce the phenomena of the polar caps by condensation and evaporation and also to produce, though rarely, some form of clouds."

Among those who have claimed to have established the existence of water vapor in Mars by the spectroscope are Rutherford, Secchi, Huggins, Janssen, and Vogel; and these declare the existence of a Martian atmosphere similar to our own in composition. Mr. Campbell can find no spectroscopic indication of an atmosphere charged with water vapor. Lewis E. Jewell says: "The spectroscopic proof of the presence of a fair amount of water in the atmosphere of Mars must be regarded as unattainable." Professor Lowell, despite the aid the admission of water vapor in Mars would give to his position, also doubts whether the spectroscope is able to detect the evidence through our own moisture-laden atmosphere.

After a minute and exhaustive study of the polar snow caps by the combined observations of Lowell, Douglass and W.H. Pickering, Mr. Lowell says: "It is interesting that the cap should so simply tell us of these three important things: the presence of air, the presence of water, and the presence of a temperature, not incomparable with that of the Earth."

Seasonal changes on Mars have long been recognized and admitted by astronomers, and these changes are on so vast a scale as to be distinctly visible from the earth. Without an atmosphere the surface of Mars would be inert. Schiaparelli was the first to notice that at successive oppositions the same regions showed different degrees of darkness and accounted for these variations by seasonal change. Mr. Denning believes that certain changes in the appearance of the markings to be due to vaporous condensations. Sir Norman Lockyer believed he saw the obscuration of a large region by clouds, this obscuration continuing for some hours. A bright spot on the terminator of Mars, discovered by Douglass at the Lowell Observatory, and which led to the newspaper excitement that signals were being made, was seen to move and finally disappear and its appearance, drift and disappearance is interpreted by Lowell as a cloud illuminated by the Sun and carried along by the wind. The presence of clouds, judging from my own brief experience, was certainly suggested at times by the peculiar way in which a large region known as Syrtis Major disappeared and flashed out again. This behavior might be expected of the tenuous lines as a result of refraction and other disturbances in our own atmosphere; when, however, a large, dark region at one time stands out firm, clear and sharp-cut as the stroke of a Japanese brush, then gradually fades out and remains obscure for some time we are inclined to believe that Sir Norman Lockyer's interpretation is true and that in such a case drifting clouds or sudden vaporous condensation produced the obscuration.

From an article on Mars by Sir Robert Ball, republished in the "Annual Report of the Smithsonian Institution" for 1900, we quote the following: "The discussion we have just given will prepare us to believe that a planet with the size and mass of Mars may be expected to be encompassed with an atmosphere. Our telescopic observations completely bear this out. It is perfectly certain that there is a certain shell of gaseous material investing Mars. This is shown in various ways. We note the gradual obscuration of objects on the planet as they approach the edge of the disk, where they are necessarily viewed through a greatly increased thickness of Martian atmosphere. We also observe the clearness with which objects are exhibited at the centre of the disk of Mars, and though this may be in some measure due to the absence of distortion from the effects of foreshortening, it undoubtedly arises to some extent from the fact that objects in this position are viewed through a comparatively small thickness of the atmosphere enveloping the planet. Clouds are also sometimes seen apparently floating in the upper region of Mars. This, of course, is possible only on the supposition that there must be an atmosphere which formed the vehicle by which clouds were borne along. It is, however, quite obvious that the extent of the Martian atmosphere must be quite insignificant when compared with that by which our Earth is enveloped. It is a rare circumstance for any of the main topographical features, such as the outlines of its so-called continents, or the coasts of its so-called seas, to be obscured by clouds to an extent which is appreciable except by very refined observations."

Professor W.H. Pickering made seven photographs of Mars on April 9, and within twenty-four hours made seven additional photographs of the same region. The second series of photographs showed an area of white extending from the polar snow cap far down toward the equator, covering a surface which he estimated to be as large as the United States. It afterwards slowly disappeared. How shall we account for this sudden apparition of a vast area of white which the photographs of twenty-four hours before did not reveal. A boy of ten, as well as the philosopher would simply say a snow-storm had taken place in Mars. Is it, then, unreasonable to picture whirling snowflakes, snow-drifts, and dazzling whiteness from the Sun's rays, and in the rapid melting of the snow, broad rivers and turbulent brooks with water areas frozen at night? But why should we be compelled to imagine as naked the surface through which these waters find their way? Soil there must be from the continual erosion of running water. The character of the rock exposures we cannot guess at, but a picture of bare rock and lifeless ground is unthinkable. Such wide-spread storms without an atmosphere could not occur. The seasonal appearance of these snows and their slow disappearance not only indicates an atmosphere, but an atmosphere disturbed by established currents which convey the moisture-laden air to regions of congelation.

A number of observers who have detected clouds in Mars described them as being yellowish in color. What more probable than that these yellowish masses are simply dust-storms such as one may often see whirling along over our American deserts? When the gusts of wind are fitful like squalls at sea, the obscuration would be fitful, to clear up again. The vast areas of desert land in Mars renders this supposition very probable. Since the above was written, my attention has been called to an early "Bulletin of the Lowell Observatory," in which Mr. Lowell, in discussing the appearance of a certain large projection on the terminator of Mars, says: "Finally, its color leads me to believe it not a cloud of water-vapor, but a cloud of dust. Other phenomena of the planet bear out this supposition."