At the request of the Editor of Scientia, I send a summary of the state of our present knowledge about the planet Mars from the work of the Lowell Observatory. I shall refer to the various facts by numerals, and thus, from their succinctness, give the reader an easy opportunity of estimating their concurrent force and of the conclusion to which they lead.
1. Mars turns on its axis in 24 hours 37 minutes 22.65 seconds. This makes its day about forty minutes longer than ours.
2. The latest determination of the position of that axis, determined at this Observatory from all the best observations up to 1905, gave for its tilt to the plane of the planet’s orbit, 24.° This determination has been incorporated in the British Nautical Almanac. Such a tilt causes seasons almost the counterpart of our own, except that orbital excentricity opportions them differently.
3. Its year consists of 687 of our days, 669 of its own.
4. It shows polar caps which melt in the Martian summer and form again in the Martian winter.
5. The making cap is of indefinite contour. It is a misty white, merging gradually into the surrounding land.
6. The melting cap, on the other hand, is bordered by a blue belt which retreats with the cap. This shows it to be the product of the disintegration of the cap. The fact excludes the possibility of its being formed of carbon dioxide, because that substance at pressures of one atmosphere or less, such as exist on Mars, passes at once from the solid to the gaseous [p. 2modifica]state. We are left, therefore, with water as the only substance we know which could give rise to this phenomenon.
7. The great melting which the polar snows undergo shows their amount not to be considerable, in spite of their extent, and indicates the deposition to be scant.
8. The surface is divided into reddish ochre and blue green tracts, the reddish green being very much the more extensive. This has the look of our reddish deserts and from its general behaviour points to that as its constitution.
9. The blue green areas, which used to be taken for water expanses, are now known not to be such because they are seamed with lines and spots permanent in place, which could not be the case were they lakes or seas.
10. They undergo a change with the Martian seasons, fading out during the winter months and deepening in tint during the summer ones. They behave, in short, like vegetation, and all the evidence points to this as their character.
11. The fact that the caps melt and reform shows, from what we have said above, the presence of water vapor in the Martian atmosphere.
12. This water vapor has registered itself on spectrograms taken by a member of the staff, Dr. Slipher. Spectra of the moon and Mars at the same altitude were recorded on the same plates and the density of the resulting water vapor band «a» proved more pronounced in the Martian spectra. Eight plates were used in all.
13. These plates have been measured by Professor Frank W. Very, giving as his result that the average layer of precipitable water in the air on Mars may be taken as 14 millimeters, while the mean value to the Earth is probably three or four times as great.
14. The fact of change upon the planet’s surface confirms the presence of a Martian atmosphere.
15. The limb light seen around the edge of the disk affords testimony to the same.
16. The planet’s low albedo proves the density of this atmosphere to be much less than our own.
17. The apparent evidence of a twilight goes to confirm this.
18. The greater melting of the south polar cap as compared with the north one indicates that the deposition [p. 3modifica]in both is light (see paper by the writer in Trans. Philosophic Society).
19. These several facts all go to show that Mars possesses an atmosphere, which, since it contains water vapor, would, from the kinetic theory of gases also contain the heavier ones; nitrogen, oxygen and carbonic acid.
20. That the amount of the water vapor corresponds more to that over our deserts than anything else on earth.
21. That the only water on the planet exists in the atmosphere and in the polar snows. Mars, therefore, is a planet which is very badly off for water and can only get a surface distribution of it by the melting of the polar caps.
From the behaviour of the polar caps due to the fact that they can be nothing but hoar frost or snow, Ave have our first evidence that the temperature on Mars is by no means very low.
22. The fact that the snow caps disappear up to 87° of latitudine, and sometimes further, shows that the temperature at times must be decidedly high.
23. Now this has been confirmed by a mathematical investigation of the writer’s, published in the Philosophic Magazine, on what the theoretic temperature should be, taking into account all the factors in the case, many of which had, in previous determinations, been omitted. The out-come of this investigation was to show that the mean temperature of Mars was probably about 8° centigrade. This is somewhat but not very much colder than the mean temperature of the Earth, which is usually taken as 15° centigrade.
24. The whole aspect of the disk bears out this conclusion. The seasons at which the melting of the polar caps begins, and the time at which it is brought to an end, at what corresponds to about the 20 th of August in our calendar, — this being the time at which the first new snow of the on-coming winter makes its appearance — all tend to show that the mean temperature must be just about what the theoretic puts it at.
25. The variations in temperature between summer and winter must, however, be very great, because of the thinness of the Martian air, and this also seems to be the case from the latitude, below 60°, to which the first snowfall reaches and the time of year at which it does so.
26. The thin air, however, is no bar to vegetation, the climate of Mars being not that of a mountain peak but of a plateau, a very different matter.
From these two factors, sufficient water and enough warmth, we see that the conditions on Mars are quite suited to habitability by organisms of some sort. This is one of the results which observations at the Lowell Observatory during the past fifteen years have established.
We now go on to the question of its present habitation by organic life, which is the one of most popular interest. Organic life needs water for its existence. This water we see exists on Mars, but in very scant amount, so that if life of any sort exists there it must be chiefly dependent upon the semi-annual unlocking of the polar snows for its supply, inasmuch as there are no surface bodies of it over the rest of the planet. Now, the last few years, beginning with Schiaparelli in 1877, and much extended since at Flagstaff haveshown:
27. The surface of the planet to be very curiously meshed by a fine network of lines and spots.
28. The better the planet has been seen, the more this singular mesh discloses itself. It is very much as if a veil was drawn over the whole surface of Mars.
29. The lines of the network are each wonderfully straight, as if they had been laid down with the utmost regularity.
30. They run into one another at definite points, sometimes as many as fourteen converging to one of these junctions.
31. Each is of the same width throughout, so far as we may observe.
32. They differ, however, as between themselves, some being much larger and more prominent than others.
33. Their average width is apparently from ten to fifteen miles, certainly not more, and of the finer sort running down to a mile or two.
34. At the places where they meet are small, round, dark spots, which have been called oases by the writer.
35. These oases are also of differing size.
36. The network has been found to extend not only over all the reddish ochre parts of the disk, but across the blue green ones as well, no part of the planet being exempt from them.
37. They end by running into one or other of the polar caps.
38. Their look is geometrical to a degree, suggesting artificiality on its face.
39. Their appearance is singularly confirmed by their behaviour.
40. During the winter season of the part of the planet in which they find themselves, they are of exceedingly tenuous proportions, only just visible with care.
41. As the polar cap begins to melt in the spring, lines are seen running out of it, deeper in tint and more imposing in size than any elsewhere to be seen on the disk.
42. As time goes on, the lines that connect with them successively darken down the latitudes.
43. Until the darkening of the network crosses the equator into the planet’s other hemisphere.
44. The arctic or antartic canals, as the case may be, lighten at the same time, and gradually this lightening, too, follows the wave of darkening which preceded it down the disk in like manner.
45. Six months after the phenomenon thus disclosed at one cap, a regular wave proceeds from the other cap down the disk in the opposite direction. Thus in every Martian year two waves of darkening affect the canal system alternately from one cap and then the other, this rythmic oscillation in appearance being exactly timed to the planet’s seasons.
46. The oases undergo a similar regular transformation. From the merest pinpoints they develop into quite sizable round spots, and then in due season fade out again to what they were before.
Now, if one considers first the appearance of this network of lines and spots, and then its regular behaviour, he will note that its geometrism precludes its causation on such a scale by any natural process and, on the other hand, that such is preciseley the aspect which an artificial irrigating system, dependent upon the melting of the polar snows, would assume. Since water is only to be had at the time it is there unlocked, and since for any organic life it must be got, it would be by tapping the disintegrated cap, and only so, that it could be obtained. If Mars be inhabited, therefore, it is precisely such a curious system we should expect to [p. 6modifica]
see, and only by such explanation does it seem possible to account for the facts.
These lines are the so-called canal of Mars. It is not supposed that what we see is the conduit itself. On the contrary, the behaviour of these lines indicates that what we are looking at is vegetation. Now, vegetation can only be induced by a water supply. What we see resembles the yearly inundation of the Nile, of which to a spectator in space the river itself might be too narrow to be seen, and only the verdured country on its banks be visible. This is what we suppose to be the case with Mars. However the water be conducted, whether in covered conduits, which seems probable, or not, science is not able to state, but the effects of it are so palpable and so exactly in accord with what such a system of irrigation would show, that we are compelled to believe that such is indeed its vera causa.