Scientia - Vol. VII/The «Canals» of Mars

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Edward Walter Maunder

The «Canals» of Mars ../Die Leitgedanken meiner naturwissenschaftlichen Erkenntnislehre und ihre Aufnahme durch die Zeitgenossen ../Il fenomeno religioso IncludiIntestazione 12 dicembre 2014 100% Da definire

Die Leitgedanken meiner naturwissenschaftlichen Erkenntnislehre und ihre Aufnahme durch die Zeitgenossen Il fenomeno religioso
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Two centuries and a half have passed since the surface of the planet Mars was first subjected to a serious examination in the telescope. Since then our knowledge of the planet has made great progress, a progress which, for the sake of convenience, we may regard as having passed through seven principal stages.

I. — In 1666, Cassini detected several distinct dark spots on Mars, and from observing these ascertained that the planet had a rotation on its axis in about 24 hours 40 minutes.

II. — In the oppositions of 1777, 1779, 1781, and 1783, Sir William Herschel determined the inclination of the axis of Mars to the plane of its orbit; measured its polar and equatorial diameters; and ascertained the amount of the polar flattening. He showed also that the white spots which formed round the poles of the planet, increased with the approach of winter, and diminished with the approach of summer, behaving therefore as the snow does in our own Arctic and Antarctic regions.

III. — In the oppositions of 1830, 1832, and 1837, Beer and Mädler, observing with a telescope of 4 inches aperture, made a series of drawings from which they were able to construct a chart of the entire globe of Mars. The features which they then drew have been recognised at every succeeding opposition, and some of them can be identified in the rough sketches of Sir William Herschel, and even in those of the year 1666, made by Hooke and Cassini. The surface of Mars therefore possesses permanent features.

[p. 254 modifica]IV. — In the opposition of 1864-5, the Rev. W. R. Dawes, observing with a telescope of 8 inches aperture, noted that in addition to the two bright white caps round the poles, there were white spots at other points of the surface. He also noted that the «seas», or dark regions of the planet, were not uniform in tone, and that the «lands» or bright regions were crossed by several long narrow lines.

V. — During the opposition of 1877, Mars was observed by a great number of astronomers, but by far the most important work was that accomplished by Schiaparelli, who continued his observations much longer after the planet had passed opposition than any other observer. It was partly in consequence of this perseverance that he detected that the bright equatorial regions of the planet were crossed by a number of narrow lines, similar to those which Dawes had shown, and mostly lying along meridians. To these lines he gave the name «canali» in conformity with the type of nomenclature adopted by previous areographers, who had divided Mars into seas, continents, islands, isthmuses, straits, and the like. But as Schiaparelli was himself careful to point out, these designations «were not intended to prejudge the nature of the spots, and were nothing but an artifice for helping the memory and shortening descriptions». And he added «we speak in the same way of the lunar seas although we well know that there are no true seas on the Moon».

The discovery of the «canals» in 1877, was the achievement of Schiaparelli that ranks the highest in popular esteem. But in the regard of astronomers, an even greater work was his micrometric triangulation of the surface of the planet; the determination of the areographic coordinates of 62 fundamental points. This work, by one who was a master in the use of the micrometer, was continued in the following oppositions, and is by far the most valuable basis that we have, for the exact delineation of the Martian surface.

VI. — In 1894, Mr Percival Lowell commenced at Flagstaff, Arizona, that persevering study of Mars which he has continued to the present time. The chief results, obtained by him, have been the detection of many new «canals», the discovery of a number of round dots, termed by him «oases» at the junctions of the «canals», and the demonstration that the «canals» and certain of the dusky regions are subject to [p. 255 modifica]strictly seasonal change, as really as the polar caps themselves. Mr Lowell observed with a refractor of 18 inches aperture.

VII. — In the opposition of 1909, M. Antoniadi observed Mars with the 33 inch refractor of the Mendon Observatory. The results of his observations will be referred to later.

The progress of the telescopic scrutiny of the planet Mars has therefore shown us a certain analogy to our own Earth. Each of its two poles is covered during its winter by a bright white substance stretching for a great distance, which may naturally be conceived to be snow. The rest of the planet is diversified with brighter and darker markings; the brighter being as a rule of a reddish ochre colour, and usually assumed to be land; whilst the darker spots, which are of a bluish-green or bluish-grey tint, were at one time supposed to represent water. But in addition to these a feature has been recognised which has no complete analogue in our terrestrial experience. «The surface of the planet is very curiously meshed by a fine network of lines and spots»; the lines being those to which Schiaparelli has given the name of «canali», the spots those that Lowell has termed «oases». It is with this network of lines and spots, i. e. of «canals» and «oases», that the present paper is concerned.

In the last number of «Scientia», Vol. VII, pages 4 and 5, Mr Lowell thus describes the appearance of these lines and spots:

«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 converge into 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.
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«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 disc, but across the blue-green ones as well, no part of the planet being exempt from them.
«38. Their look is geometrical to a degree, suggesting artificiality on its face».

In numerous places elsewhere, Mr Lowell insists further upon the perfect regularity of the lines, the «canals», and the perfect circularity of the spots, the «oases». «So far as it is possible to make out, there is no perceptible difference in width of a canal, when fully developed, from one end of it to the other. Certainly it takes a well-ruled line on paper to look its peer for regularity and deportment». («Mars as the Abode of Life», page 149).

And Mr Lowell takes the regularity of the lines, and the circularity of the spots, as proof that both the one and the other are artificial; the designed work of intelligent craftsmen: «That the lines should follow arcs of great circles, whatever their direction, is as unnatural from a natural standpoint as it would be natural from an artificial one; for the arc of a great circle is the shortest distance from one point upon the surface of a sphere to another. It would therefore, if topographically possible, be the course to take to conduct water, with the least expenditure of time or trouble, from the one to the other. The circular shape of the oases is as directly economic as is the straightness of the canals; for the circle is the figure which incloses the maximum area for the minimum average distance from its centre to any point situated within it. In consequence if a certain amount of country were to be irrigated, intelligence would suggest the circular form in preference to all others, in order thus to cover the greatest space with the least labor». («Mars», page 187).

There have been two entirely different controversies as to the «canals» of Mars. The first arose immediately on the publication of Schiaparelli’s 1877 observations. Several astronomers of great skill and experience had observed the planet during that opposition without detecting the network which Schiaparelli had revealed, and it was natural that they should display a certain reluctance in accepting results so novel and [p. 257 modifica]so strange. But little by little this controversy has passed. We now know that the «canals» vary much in their visibility, and «curiously enough, the canals are most conspicuous not at the time the planet is nearest to the earth and its general features are in consequence best seen; but as the planet goes away, the canals come out. The fact is that the orbital position and the seasonal epoch conspire to a masking of the canal phenomena». («Mars as the Abode of Life», page 167). This was the chief reason why Schiaparelli’s discoveries seemed at first to stand so entirely without corroboration; the «canals» did not become conspicuous until after most observers had desisted from following the planet. Another reason was that in 1877 Mars was low down in the sky for northern observatories, and good definition is an essential for their recognition. Nevertheless, some English astronomers had delineated a few of the easiest and most conspicuous of the «canals» in 1877, before any rumour of Schiaparelli’s work had reached England. I may mention that I had myself thus drawn the Ulyxis Fretum, the Oceanus, the Agathodaemon, the Eosphorus, the Phasis and the Eunostos.

That controversy has long ago passed away. As Mars came under observation again and again, at successive oppositions, the number of those who were able to verify Schiaparelli’s discoveries, increased, and we have long known that the great Italian astronomer was not the victim of any optical illusion; there were actual markings on the planet Mars, where he had represented them; markings which, when seen under like conditions and with equal instrumental equipment, did present the appearance of straight narrow lines. The «canals» of Mars are real markings, not imaginary ones.

The second controversy is very different from the first, and seems to have first arisen out of an unfortunate mistranslation of the term chosen by Schiaparelli to indicate these linear streaks. «Canal» in English means an artificial waterway, whilst «channel» generally means a natural one, and the idea has been very skilfully developed by Mr Lowell that the regularity of the «canals» and «oases» quite precludes their being natural formations. Hence he considers that we are shut up to the idea that Mars is inhabited by a race of engineers of superhuman intelligence and power, who [p. 258 modifica]are fighting a losing battle, against the gradual desiccation of their planet, by means of a Titanic system of irrigation.

What has been the reason which has induced Mr Lowell to put forward an idea so little in accordance with the conclusions of astronomers in general? It is this. Just as he sees the «canals», so he fails to detect in them any evidence of detail or irregularity. They appear to him like pen-and-ink lines drawn with a ruler. The question between him and his critics is not, and has never been, a question as to the existence of certain apparently straight, narrow streaks on Mars. There are indeed a number of discrepancies between different observers to be readily explained by differences of eyesight, atmospheric conditions, telescopic power, and the like, but there is good substantial agreement as to the main details.

But what Mr Lowell contends is this: that the perfect regularity of form and position which he gives to the «canals» in his representations of the planet, proves that they are artificial objects — they are too regular to be natural — his assumption being that no improvement in telescopes, no increase in experience, no better eyesight, will ever break up that regularity into finer and more complex detail, but that it represents Mars as we should see it, if we were close to the planet itself.

But the history of our knowledge of the planet’s surface teaches us a very different lesson. If we turn to the drawings made by Beer and Mädler in 1830, two small objects, exceedingly like one another, appear repeatedly. These are two dark circular spots; the one isolated, the other at the end of a gently curved line. Both spots recall the «oases» of Mr Lowell, and the curved line at the termination of which one of the spots appears, represents closely the appearance presented in recent observations by several of the «canals». There can be no doubt that in the year 1830, no better drawings of Mars had appeared and that in representing these two spots as truly circular, and the curved line as narrow, sharp and uniform, Beer and Mädler pourtrayed the planet as they actually saw it. The one marking we call to-day the Lacus Soils, the other, the Sinus Sabaeus, and we can trace the gradual growth of our knowledge of both markings from 1830 up to the present time. These two [p. 259 modifica]regions are shown very clearly on drawings by the four observers mentioned in the first part of this paper, — Dawes in 1864, Schiaparelli in 1877 and later, Lowell in 1895 and later, and Antoniadi in the opposition just passed. Now if we compare the drawings of Beer and Mädler made with a telescope of 4 inches aperture, with those of Dawes made with one of 8 inches, we see that the resemblance between the Lacus Solis and the head of the Sinus Sabaeus has entirely vanished, and that neither now appears as a plain circular dot. Thirteen years later, Schiaparelli with the same aperture as Dawes, showed about the same amount of detail, to which he was able to add in later years. Again Lowell in 1894 and subsequently, was able to show further detail with an aperture of 18 inches; whilst with 33 inches, in 1909, Antoniadi brought out a mass of structure in the regions which were so simple in the sight of Beer and Mädler.

Now the gradation in size from the Lacus Solis down to the smallest «oasis» of Lowell is a complete one. Dare we say, if a future development in the power of telescopes should equal the advance made from the 4-inch of Beer and Mädler to the 33-inch of Meudon, that the «oases» of Mr Lowell will refuse to yield to such improvement, and will still show themselves all, as uniform, circular spots? Translate this thought into terms of the past. Would Beer and Mädler have been justified in arguing that the apparent perfect circularity of the two «oases» which they observed, proved that they were artificial formations made circular, «for the circle is the figure which incloses the maximum area for the minimum average distance from its centre to any point situated within it?». («Mars», page 187).

Would not the answer have been valid that a spot too small to be defined must appear circular, since its minor irregularities are invisible, and that therefore the apparent circularity probably covered detail of an altogether different form? We know that it would. Yet it is that same argument in a stronger form against which Mr Lowell is contending to-day.

Beer and Mädler only drew two of these spots; Lowell shows 186. Beer and Mädler’s two spots seemed to them precisely alike; these two spots, as we see them to-day, bear not the slightest resemblance to each other. Mr Lowell’s 186 or more «oases» (with a few exceptions) appear all of the [p. 260 modifica]same character; is it possible to suppose, if telescopes develop in the future as they have done in the past, that Mr Lowell’s 186 «oases» will continue to present the same uniformity of appearance, any more than the two spots observed by Beer and Mädler?

Further, if we give a novice a small telescope and set him to observe Mars, he will draw the Lacus Solis and the Sinus Sabaeus just exactly as Beer and Mädler did, as two round uniform spots, And the same observer as he gains experience and his instrumental power is increased, will draw those same regions as Dawes and Schiaparelli have shown them. It is no question of planetary change; it is a question of experience and of «seeing».

There is a much simpler explanation of the regularity of the «canals» and «oases» than to suppose that an industrious population of geometers have dug them out or planted them. We know that a telegraph wire seen against a background of bright cloud can be discerned at an amazing distance. For average normal sight, the wire need only subtend a breadth of a second of arc to be thus discerned, and the perception of the wire will be quite unmistakeable. At the same time, it would be quite untrue to say that the perception of the wire was of the nature of defined vision, as will be seen at once when small objects of different form are being experimented with. If instead of a wire of very great length, extending right across the field of view of both eyes, a short line be drawn on a white ground, it will be found that as the length of the line is diminished below a certain point, so its breadth must be increased, and that by the time that the length has been diminished to half a minute of arc the breadth must have been increased to that same amount. The object then, whatever its actual shape, can be just recognised as a small circular spot. The limit for the average observer is indeed a little greater than this, being about 34 seconds of arc.

But even here, though a black spot 34 seconds in diameter, on a white ground, can be perceived, we have not yet attained to defined vision. For, if we place two black spots, each 34 seconds of arc in diameter, near each other, they will not be seen as separated spots, unless they are 4 minutes of arc apart. Nearer than that, they will give the [p. 261 modifica]impression either that they form one circular spot, or an oval one, or even a uniform straight line, according to the amount of separation. If two equal round spots be placed, so that the distance between their centres is equal to two diameters, then the diameter of each spot must be at least 70 seconds, for them to be distinctly defined, that is to say, for the spots to be seen as two separate objects.

It will be seen that there is a very wide range between objects which are large enough to be quite unmistakeably perceived, and objects which are large enough to have their true outline really defined. It is a question of seconds of arc in the one case, and minutes of arc in the other.

This depends upon the structure of the eye and the retina; the eye being essentially a lens with its defining power necessarily limited by its aperture, and the retina a sensitive screen, built up of an immense number of separate elements, each of which can only transmit a single sensation. Different eyes will have different limits, both for the smallest object that can be discerned, and for the smallest object that can be defined, but for any sight the range between the two will be of the order just indicated. Between these two limits, — the limit of discernment and the limit of definition, — objects can only appear under the two forms of straight lines and of round spots. Mr Lowell is justified in drawing attention to «the strangely economic character of both the canals and oases in the matter of form». («Mars», page 187). Straight lines and circles are economic forms, but they are economic not only in hypothetical hydraulic undertakings, but also in vision. «The circle is the figure which incloses the maximum area for the minimum average distance from its centre to any point situated within it»; («Mars», page 187); therefore if a small spot be perceived by the sight, but be too small to have its actual outline defined, it will be recognised by the eye as truly circular, on the principle of economy of effort. So again a straight line is the shortest that can be drawn between two points, and a straight line can be perceived as such when of an angular breadth quite 40 times less than that of the smallest spot. A straight line is that which gives the least total excitement in order to produce an appreciable impression, and therefore the smallest appreciable impression produces the effect of a straight line.

[p. 262 modifica]It follows therefore that, if the actual surface of Mars were really covered by a network of straight lines, like those represented on the charts which we owe to Mr Lowell, there could be no doubt, no controversy about their existence. Every observer would see them, since an actual straight line can be seen when its angular breadth is very far indeed below the limit of vision for any other form.

It is sufficient then for us to suppose that the surface of Mars is dotted over with minute irregular markings. If these are fairly near each other, it is not necessary in order to produce the effect of «canals», that they should be individually large enough to be seen, nor is it necessary that these markings should approximately be circular in actual form. They may be of any conceivable shape, provided only that they are separately below the limit of defined vision, and are sufficiently sparsely scattered. In this case the eye inevitably sums up the details which it recognises, (but cannot resolve) into lines, essentially canal-like in character. Wherever there is a slight aggregation of these minute markings, we shall have the impression of a circular spot, or to use Mr Lowell’s nomenclature, an «oasis». If the aggregation be greater still, and more extended, we shall have a shaded area, — a «sea».

The above considerations arise from simple experiments with the unaided eye, but the same principle apply yet more strongly to telescopic vision. I would refer the reader to a series of valuable papers on this subject by Dr G. Johnstone Stoney in the «Philosophical Magazine» Vol. XVI, pp. 318, 796, and 950 (1908, Aug., Nov., and Dec.). It need simply be noted here, — since the images of a mathematical point, and of a mathematical line are not represented by a telescope as a mathematical point and line respectively, but as small surfaces, — that minute irregularities are inevitably smoothed out by the telescope. A magnifying power of 250 applied to a telescope directed on the Moon will not show the lunar structure so well, as we should see it without a telescope, if it were brought within a thousand miles of us. Mars, at its nearest approach, is more than 150 times the distance of the Moon, yet certainly no observer, using a magnifying power of 150 has ever seen Mars as well as we can see the full Moon with naked eye. I am of course allowing for the fact that Mars has double the diameter of the Moon. Telescopic vision, [p. 263 modifica]moreover, is monocular; our unassisted sight is binocular, and therefore the more efficient in the recognition of minute detail. Telescopic vision, therefore, increases the tendency to display minute markings under the two «economic» forms of straight lines and circular spots.

When we come to photographs, the process is carried to a third stage. The image is formed by the telescope and is received on a plate essentially granular in structure, and is finally examined by the eye. The granular structure of the plate acts as a third factor in reducing irregularities and simplifying details; a third factor in producing the two simplest types of form, the straight line and the circular spot.

The above conclusions were reached by me in the year 1891, whilst reviewing a paper by M. Camille Flammarion in which the latter gave a number of instances in which sunspots were seen with the naked eye. I was surprised to note how often groups of spots of relatively small total area had been seen, whilst others very considerably larger had escaped detection. I therefore for some time watched the sun on every available occasion without any optical assistance except that of an ordinary dark glass, and found that, I could often recognise the presence of a straggling group of small unimportant spots as a short «canal», when a single spot of considerably greater total area was quite invisible. These observations and the experiments which followed them, led me to the conclusion that in all probability the «canals» of Mars were simply the summation of a complexity of detail far too minute to be separately discerned. («Knowledge», 1894, pp. 249-252, and 1895, p. 58).

A little later, in his work «Marte nel 1896-97», Dr Cerulli independently arrived at the same conclusion and wrote «These lines are formed by the eye.... which utilises.... the dark elements which it finds along certain directions»; that «a large number of these elements forms a broad band»; and that «a smaller number of them gives rise to a narrow line». Also «the marvellous appearance of the lines in question has its origin, not in the reality of the thing, but in the inability of the present telescope to show faithfully such a reality». Then, pushing the theory further, Dr Cerulli discovered the remarkable fact that an opera glass reveals «canals» on the Moon, while in a recent letter to M. Antoniadi, he showed [p. 264 modifica]that small photographs of our satellite about 1 centimetre in diameter, if held at the proper distance, reveal, after prolonged staring, single and double «canals» on the Moon as on Mars.

In 1907 Prof. Newcomb made some experiments in the same directions as those by Dr Cerulli and myself, and reached the same general conclusion. He further drew attention to the extent to which the «canal» system as then known, — Mr Lowell had named and catalogued 398, — covered the surface of the planet. «Making due allowance for the aberration of the best achromatic telescope, the total area of the entire system of 400», as depicted on the retina of the terrestrial eye, can scarcely fall much below one half the total area of the planet, and may be greater». Since then the number of «canals» has been increased, so that now their area as depicted on the retina, must be fully two-thirds the area of the planet.

Whilst there is still controversy as to the true nature of these straight lines and round spots on the surface of Mars it is well to bear in mind that there are many facts about the planet that are not in dispute.

The length of the year of Mars is 669 days as reckoned in Martian time; or 687 as reckoned in terrestrial time. Of these 199 days belong to the spring of the northern hemisphere, 183 to summer, 147 to autumn, and 158 to winter; or the summer half includes 382, and the winter 305 days. The mean distance from the Sun, that of the Earth being unity, is 1.5237, and in consequence the light and heat received from the Sun, per unit of surface, is only 0.43 of that received by the Earth, or about three-sevenths. The diameter surface, volume, mass and density of Mars are respectively 0.53, 0.281, 0.1489, 0.107, and 0.72 of the same values for the Earth, and the force of gravity at its surface is 0.381. It follows that the atmosphere of Mars is arranged in a very different manner from that of the Earth; the barometric gradient is much less steep. From this circumstance, and from the feebler force of gravity, the atmospheric circulation must be relatively languid and slow. The level of half-surface-pressure is reached at three and a third miles on the Earth, but not until eight and three-quarter miles on Mars. Assuming that the mass of the atmosphere bears the same relation [p. 265 modifica]to the total mass of the planet for both the Earth and Mars, the atmospheric pressure on Mars would be about one-seventh that on the Earth, or 2 lbs to the square inch. But in spite of this low pressure at the surface, at about 15 miles, or 24 kilometres, above the surface of the two planets, the Martian atmosphere is as dense as ours, and above that level, is the denser of the two. It is probable that the average height at which meteors become incandescent is double as great on Mars as with ourselves. The Martian atmosphere, though much less dense than the terrestrial, is therefore distinctly deeper.

But since we see the surface of Mars so clearly, although the atmosphere is so deep, it is evident that the above estimate of its density must be a maximum. In all probability the pressure at the surface is considerably under 2 lbs to the square inch; it certainly cannot be greater.

With an atmospheric pressure of 2 lbs to the square inch, water will boil at about 44° centigrade. But this means a great diminution of the range of temperature, through which it is possible for water to remain in the liquid state. The mean temperature of the Earth is usually taken as about 15° centigrade, whilst the range from freezing to boiling point is 100°. The two facts taken together imply that the liquid form is the one in which water is usually found upon our planet, though the nearness of the mean to the freezing point suggests that, in the polar zones, it must normally take the forms of ice and snow.

Now the mean temperature of Mars must be considerably below that of the Earth, seeing that it receives, surface for surface, but three-sevenths as much of the solar heat But. even on the Earth, on high plateaux and mountains, the range in the daily temperature of the soil is enormous, amounting sometimes to 100° centigrade. The range must be even greater still for Mars, and the opportunity for water to remain in the liquid form, must be much diminished; its normal form must be snow or vapour. It will be easily congealed, easily evaporated. Day by day, at least in the tropical and sub-tropical regions, evaporation will proceed readily; night after night severe frosts will succeed. At dawn probably therefore the air is dry; during the afternoon, it may be saturated. This heating of the region in daylight, and [p. 266 modifica]refrigeration of that in night, will set up the chief winds known to Mars, — its morning and evening breezes, — and the chief atmospheric change will be the condensation of the water vapour beginning a little before sunset; and the melting and evaporation of the frost produced during the night, beginning soon after sunrise. It is clear that the frozen condition of the water of Mars must extend further into the area in daylight along the arc of sunrise, than along the arc of sunset; the sun will take some time after rising to make its power felt. Both terminators have been observed to be fringed by a white line but the white fringe to the sunrise terminator has been noticed by several observers to be distinctly broader than that of the sunset terminator.

So far we have looked at the tropical regions of Mars.

When we turn our attention to the poles, a most important circumstance has to be considered, namely, that for a period, very nearly equal to an entire year of the Earth, each pole of Mars, in turn, is subjected continuously to the solar rays. Indeed the northern pole is so exposed for more than a terrestrial year. There is no need for surprise that under such conditions, the polar snowcaps, and especially the northern one, should sometimes disappear altogether. But that they do diminish to a degree so far surpassing the diminution of the terrestrial polar caps, is a clear indication that the amount of moisture present on the planet is relatively very small; and the narrowness of the white fringe to the sunrise and sunset terminators, is a further confirmation of this fact.

We have already seen that the chief atmospheric circulation of the planet must be that which goes on between the sunlit hemisphere and the hemisphere in darkness. Looking at Mars from the view-point of the Sun — and our own view-point does not greatly differ from this — we may expect that there will be a general cold current close to the ground, blowing inward from the circumference of the disc towards the centre, but prevailing only for a relatively small distance from the circumference. In the centre of the disc there will be ascendin currents, flowing towards the circumference. This general scheme of circulation will of course, not be symmetrical; the hottest part of the day with Mars, as with the Earth, will be in the afternoon.

[p. 267 modifica]But this general scheme will be profoundly modified by the fact that the polar region is continually presented to the Sun, so that probably there will come a time in the progress of its summer when it will be the hottest part of the entire planet. The pole that is enjoying the summer, therefore, more than even the tropics, will be the centre from which the heated air will radiate. Similarly, the pole in winter will be the ultimate focus towards which these heated currents will direct their course, as it will undoubtedly be the coldest region of the planet — far colder than our extremest earthly experience.

On the Earth, aqueous circulation is carried on both by ocean currents and by the transportation of water through the air. There is nothing on Mars to correspond to the vast ocean surfaces of the Earth and from the ease with which water will pass into vapour, it is clear that we must look to the atmospheric circulation as the chief means for the transference of moisture from one region to another.

And indeed this is readily admitted by all writers on Martian meteorology, so far as it relates to the transfer of moisture to the poles; it is only when the question of the movement in the opposite direction arises that it is assumed to be impossible that the moisture should travel in the form of vapour, and it is found imperative to cover Mars with a Titanic system of irrigation works fitted with mammoth pumping stations at short intervals. Yet the atmospheric circulation of Mars cannot be always in one and the same direction. If anything, one would suppose that the winds blowing in summer time from the melting pole cap, would be more heavily laden with vapour than those blowing in winter towards the freezing cap.

«Canals», — artificial waterways, — are therefore not necessary in order that the succession of the seasons should mean the transfer of moisture from one region to another, nor has there ever been any valid reason for supposing that such exist on the planet. The only pretext for such a supposition lay in the apparent precise and geometrical regularity of the «canals» and «oases». Yet even as far back as 1884, some of the «canals» were losing their strict rectilinear appearance to Schiaparelli; and later Barnard, Cerulli, Denning, Millochau, Molesworth, Phillips, Stanley Williams, and others [p. 268 modifica]have found them to show evident signs of resolution. Antoniadi reporting to the Journal of the British Astronomical Association for December 1909, on his work with the 33-inch telescope of the Meudon Observatory, states:

«Fifty «canals» having some real basis were seen at Meudon. Of these, 28 per cent were resolved into disconnected knots of diffuse shadings; 20 per cent, appeared as more or less dark bands; 16 per cent, were edges of faint shadings; another 16 per cent. seemed to be broad and diffused streaks; 8 per cent. were seen as irregular lines; 6 per cent swelled out into vast shadings; and another 6 per cent had the form of irregular isolated «lakes».»

«The tendency to resolution was irresistible under favourable circumstances, and were all parts of the surface to have been examined under equally advantageous conditions, the percentage of «canals» breaking up into their larger components would have been far greater than that here given».

From his observations (1909 September 20 to November 27) M. Antoniadi was led to deduce the following general inferences:

I. The true appearance of the planet Mars is a natural one, and comparable to that of the Earth and of the Moon,
II. Under good seeing there is no trace whatever of a geometrical network.
III. The «continental regions» of the planet are variegated with innumerable dusky spots of very irregular outline and intensity, whose sporadic groupments give rise, in small telescopes, to the «canal» system of Schiaparelli.

M. Antoniadi continues:

«No doubt we have never seen a single genuine canal on Mars; nor should we see any from Phobos, the nearest satellite to the planet».

«On October 6 and on November 9, it was given to the Director (M. Antoniadi) to witness what he considers to be an elementary view of the true structure of the Martian deserts. The image was slightly tremulous in each case, when, suddenly, definition becoming perfect, a wonderful sight presented itself for a dozen seconds on both occasion. The soil of the planet then appeared covered with a vast number of dark knots and chequered fields, diversified with the faintest imaginable dusky areas, and marbled with irregular [p. 269 modifica]undulating filaments, the representation of which was evidently beyond the powers of any artist. There was nothing geometrical in all this — nothing artificial, the whole appearance having something overwhelmingly natural about it».

In the November number of the same Journal, M. Antoniadi gives four exquisite drawings of Mars, which should be compared with drawings of the same regions obtained by our chief areographers at different epochs, and with different apertures, as illustrating the increasing revelation of minute detail on the planet, as telescopic power has been increased, and experience has been gained. The «geometrical network» was a stage, a necessary stage in our progress, but it has already been passed, and M. Antoniadi concludes his December report by «pointing out that it vanished when the planet was practically at its closest approach to the Earth, high above the horizon, and scrutinized with the best instruments of our time. And the fact that no straight lines could be held steadily when much more delicate detail was continually visible, constitutes a fatal objection to their crumbling existence».

«But the Director is glad at last to be in a position to do justice and honour to Professor Schiaparelli’s monumental work, and to affirm that, as far as it was possible to judge, (the planet being partly veiled by cloud lately) wherever the distinguished Italian astronomer had drawn a streak, there was a group of irregular shadings on the surface of Mars».

Greenwich, Royal Observatory.