THE ILLUSIONS OF MARS
The two preceding chapters have led to two opposing, two incompatible
conclusions. In Chapter VI, a summary was given of Prof. Lowell's claim to
have had ocular demonstration of the handiwork of intelligent organisms on
Mars. In Chapter VII, it was shown that the indispensable condition for
living organisms, water in the liquid state, is only occasionally present
there, the general temperature being much below freezing-point, so that
living organisms of high development and more than ephemeral existence are
impossible.
Prof. Lowell argues that the appearance of the network of lines and spots
formed by the canals and oases, and its regular behaviour, "preclude its
causation on such a scale by any natural process," his assumption being
that he has obtained finality in his seeing of the planet, and that no
improvement in telescopes, no increase in experience, no better eyesight
will ever break up the perfect regularity of form and position, which he
gives to the canals, into finer and more complex detail.
But the history of our knowledge of the planet's surface teaches us a
different lesson. Two small objects appear repeatedly on the drawings
made by Beer and Maedler in 1830; these are two similar dark spots, the one
isolated, the other at the end of a gently curved line. Both spots
resemble in form and character the oases of Prof. Lowell, and the curved
line, at the termination of which one of the spots appears, represents
closely the appearance presented by several of the canals. In the year
1830 no better drawings of Mars had appeared; and in representing these
two spots as truly circular and the curved line as narrow, sharp, and
uniform, Beer and Maedler undoubtedly portrayed the planet as actually they
saw it. The one marking was named by Schiaparelli the Lacus Solis, the
other, the Sinus Sabaeus, and they are two of the best known and most
easily recognized of the planet's features; so that it is easy to trace
the growth of our knowledge of both of them from 1830 up to the present
time. They were drawn by Dawes in 1864, by Schiaparelli in 1877 and the
succeeding years, by Lowell in 1894 and since, and by Antoniadi in 1909
and 1911. But whereas the drawings of Beer and Maedler, made by the aid of
a telescope of 4 inches aperture, show the two spots as exactly alike, in
those of Dawes, made with a telescope of 8 inches, the resemblance between
the two has entirely vanished, and neither is shown as a plain circular
dot. Since then, observers of greater experience and equipped with more
powerful instruments have directed their attention to these two objects,
and a mass of complicated structure has been brought out in the regions
which were so simple in the sight of Beer and Maedler, so that not a trace
of resemblance remains between the two objects that to them appeared
indistinguishable.
Now the gradation in size, from the Lacus Solis down to the smallest oasis
of Lowell, is a complete one. If a future development in the power of
telescopes should equal the advance made from the 4-inch of Beer and
Maedler, to the 33-inch which Antoniadi used in 1909, is it reasonable to
suppose that Prof. Lowell's oases will refuse to yield to such
improvement, and will all still show themselves as uniform spots,
precisely circular in outline? It is clear that Beer and Maedler would have
been mistaken if they had argued that the apparently perfect circularity
of the two oases which they observed proved them to be artificial, because
the increase in telescopic power has since shown us that neither is
circular. The obvious reason why they appeared so round to Beer and Maedler
was that they were too small to be defined in their instruments; their
minor irregularities were therefore invisible, and their apparent
circularity covered detail of an altogether different form.
Beer and Maedler only drew two such spots; Lowell shows about two hundred.
Beer and Maedler's two spots seemed to them exactly alike; these two spots
as we see them to-day have no resemblance to each other. Prof. Lowell's
two hundred oases, with few exceptions, seem all of the same character; is
it possible to suppose, if telescopes develop in the future as they have
done in the past, that the two hundred oases will preserve their
uniformity of appearance any more than the Lacus Solis and the head of the
Sinus Sabaeus? If a novice begins to work upon Mars with a small telescope,
he will draw the Lacus Solis and the Sinus Sabaeus as two round, uniform
spots, and as he gains experience, and his instrumental power is
increased, he will begin to detect detail in them, and draw them as Dawes
and Schiaparelli and others have shown them later. 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; it is connected with the nature of vision.
A telegraph wire seen against a background of a bright cloud can be
discerned at an amazing distance--in fact, at 200,000 times the breadth of
the wire; a distance at which the wire subtends a breadth of a second of
arc. For average normal sight the perception of the wire will be quite
unmistakable, but 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 would
be seen at once if small objects of irregular shape were threaded on the
wire; these would have to be many times the breadth of the wire in order
to be detected. Again, if instead of a wire of very great length extending
right across the field of view of both eyes, a short, black 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. If the
observer is distant from the line 6000 times its length, then the breadth
must be increased to be equal to the length, and the object, whatever its
actual shape, can be just recognized as a small circular spot, which will
subtend about 34 seconds of arc.
But though a black spot, 34 seconds in diameter, can be perceived on a
white ground, 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 separate spots unless there is a clear space between
them of six times that amount. Nearer than that they will give the
impression 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 of arc 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 wide range between objects that are large
enough to be quite unmistakably 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 of minutes of arc in the other. Within
this range, between the limit at which objects can be just perceived and
that where they can be just defined, objects must all appear as of one of
two forms--the straight line and the circular dot.
This depends upon the structure of the eye and of 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 objects which can be discerned and for the smallest objects that
can be defined, but for any sight the range between the two will be of the
order just indicated.
Prof. Lowell has drawn attention to the "strangely economic character of
both the canals and oases in the matter of form." It is true that straight
lines and circles are economic forms, but they are economic not only in
the construction of irrigation works but also in vision. "The circle is
the figure which encloses the maximum area for the minimum average
distance from its centre to any point situated within it;" therefore, if
a small spot be perceived by the sight but be too small to have its actual
outline defined, it will be recognized by the eye as being 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.
It is sufficient, then, for us to suppose that the surface of Mars is
dotted over with minute irregular markings, with a tendency to aggregate
in certain directions, such as would naturally arise in the process of the
cooling of a planet when the outer crust was contracting above an
unyielding nucleus. If these markings 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. They may be of any conceivable
shape, provided 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 recognizes but cannot resolve)
into lines essentially "canal-like" in character. Wherever there is a
small aggregation of these minute markings, an impression will be given
of a circular spot, or, to use Prof. Lowell's nomenclature, an "oasis." If
the aggregation be greater still and more extended, we shall have a shaded
area--a "sea."
The above remarks apply to observation with the unaided eye, but the same
principle applies yet more strongly to telescopic vision. No star is near
enough or sufficiently large to give the least impression of a true disc;
its diameter is indistinguishable; it is for us a mathematical point,
"without parts or magnitude." But the image of a star formed by a
telescope is not a point but a minute disc, surrounded by a series of
diffraction rings. This disc is "spurious," for the greater the aperture
of the telescope the smaller the apparent disc.
That which holds good for a bright point like a star holds good for every
individual point of a planetary surface when viewed through the telescope;
that is to say, each point is represented by a minute disc; all lines and
outlines therefore are slightly blurred, so that minute irregularities are
inevitably smoothed out.
When we come to photographs, the process is carried to a third stage. The
image is formed by the telescope, subject to all the limitations of
telescopic images, 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 the third factor in concealing irregularities and
simplifying details; a third factor in producing the two simplest types of
form--the straight line and the circular dot.
Prof. Lowell describes the canals as like lines drawn with pen, ink and
ruler, but not a few of our best observers have advanced much beyond this
stage. Even as far back as 1884, some of the canals were losing their
strict rectilinear appearance to Schiaparelli, and the observers of the
planet who have been best favoured by the power of the telescope at their
disposal, by the atmospheric conditions under which they worked, and by
their own skill and experience--such as Antoniadi, Barnard, Cerulli,
Denning, Millochau, Molesworth, Phillips, Stanley Williams and
others--have found them to show evident signs of resolution. Thus, in
1909, Antoniadi found that of 50 canals, 14 were resolved into
disconnected knots of diffused shadings, 4 were seen as irregular lines,
10 as more or less dark bands; and he found that, in good seeing, there
was no trace whatever of the geometrical network.
The progress of observation, therefore, has left Prof. Lowell behind, and
has dispelled the fable which he has defended with so much ingenuity. But,
indeed, there never was any more reason for taking seriously his theory as
to the presence of artificial waterways on Mars than for believing in the
actual existence of the weird creatures described by H. G. Wells in the
_War of the Worlds_.
There are too many oversights in the canal theory.
Thus no source is indicated for the moisture supposed to be locked up in
the winter pole cap. Prof. Lowell holds that there are no large bodies of
water on the planet; that the so-called seas are really cultivated land.
In this case there could be little or no evaporation, and so no means by
which the polar deposits could be recruited.
Yet it is certain that the supply of the winter pole cap must come from
the evaporation of water in some region or other. And here is another
oversight of the artificial canal theory. The canals are supposed to be
necessary for the conveyance of water from the pole towards the equator;
although, as this was "uphill," vast pumping stations at short intervals
had to be predicated. But it is not supposed that the water needed to
travel by way of the canals to the poles. If, however, the moisture is
conveyed as vapour through the atmosphere to the pole as winter
approaches, it cannot be impossible that it should be conveyed in the same
manner from the pole as summer draws on, and in that case the artificial
canals would not be needed. If the canals are necessary for conveying the
water in one direction, they would be necessary for the opposite
direction. But there would be something too farcical in the idea of the
careful Martians dispatching their water first to the pole to be frozen
there, and then, after it had been duly frozen and melted again, fetching
it back along thousands of miles and through numerous pumping stations for
use in irrigating their fields.
Of all the many hundreds of canals only a few actually touch the polar
caps. But on the theory that the entire canal system is fed by the polar
cap in summer, the carrying capacity of the polar canals should be equal
to, if not greater than, that of the entire system outside the polar
circle. A glance at the charts of the planet shows that the polar canals
could not supply a twentieth part of the water needed for those in the
equatorial regions. Another oversight is that of the significance of the
alleged uniformity and breadth of the canals. Prof. Lowell repeatedly
insists that the canals are of even breadth from end to end, and spring
into existence at once throughout their whole length. This statement is in
itself a proof that the canals cannot be what he supposes them to be. An
irrigation system could not have these characteristics; the region
fertilized would take time to develop; we should see the canal extending
itself gradually across the continent, and its breadth would not be
uniform from end to end, but the region fertilized would grow narrower
with increase of distance from the fountain head of the canal.
Under what conditions can we see straight lines, perfectly uniform from
end to end, spring into existence, in their entirety, without going
through any stages of growth? When the lines are not actual images, but
are suggested by markings perceived, but not perfectly defined. In 1902
and 1903, in conjunction with Mr. Evans, the headmaster of Greenwich
Hospital School, I tried a number of experiments on this point, with the
aid of about two hundred of the boys of the school. They had several
qualifications in respect of these experiments; they were keen-sighted,
well drilled; accustomed to do what they were told without asking
questions; and they knew nothing whatsoever of astronomy, certainly
nothing about Mars.
A diagram was hung up, based upon some drawing or other of the planet made
by Schiaparelli, Lowell or other Martian observer, but the canals were not
inserted; only a few dots or irregular markings were put in here and
there. And the boys were arranged at different distances from the diagram
and told to draw exactly what they saw. Those nearest the diagram were
able to detect the little irregular markings and represented them under
their true forms. Those at the back of the room could not see anything of
them, and only represented the broadest features of the diagram, the
continents and seas. Those in the middle of the room were too far off to
define the minute markings, but were near enough for those markings to
produce some impression upon them; and that impression always was of a
network of straight lines, sometimes with dots at the points of meeting.
Advancing from a distance toward the diagram the process of development
became quite clear. At the back of the room no straight lines were seen;
as the observer came slowly forward, first one straight line would appear
completely, then another, and so on, until all the chief canals drawn by
Schiaparelli and Lowell in the region represented had come into evidence
in their proper places. Advancing still further, the canals disappeared,
and the little irregular markings which had given rise to them were
perceived in their true forms.
These experiments at the Greenwich Hospital School were merely the
repetition of similar ones that I had myself made privately twelve years
earlier, leading me to the conclusion, published in 1894, that the canals
of Mars were simply the summation of a complexity of detail too minute to
be separately discerned.
A little later, in his work "_Marte nel 1896-7_," Dr. Cerulli
independently arrived at the same conclusion, and wrote: "These lines are
formed by the eye ... which utilizes ... the dark elements which it finds
along certain directions"; and "a large number of these elements forms a
broad band"; and "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." In 1907, Prof. Newcomb made
some experiments in the same direction and reached the same general
conclusion. More recently still, Prof. W. H. Pickering has worked on the
same lines and with the same result. The venerable George Pollock,
formerly the Senior Master of the Supreme Court and King's Remembrancer,
sent to me, in his 91st year, the following note as affording an apt
illustration of the true nature of the canaliform markings on Mars:
"On Saturday last, journeying in a motor-car, I came into a broad road
bounded by a dark wood. Looking up I was amazed to see distinct,
well-defined, vertical, parallel white lines, the wood forming the dark
background. On getting nearer, these lines resolved themselves into spots,
and they proved to be the white insulators supporting the telegraph
wires."
Prof. Lowell has objected that all experiments and illustrations of this
kind are irrelevant; only observations upon the planet itself ought to be
taken into account.
But such observations have been made upon the planet itself with just the
same result. Observers have seen streaks upon Mars--knotted, broken,
irregular, full of detail--and when the planet has receded to a greater
distance, the very same marking has shown itself as a narrow straight
line, uniform from end to end, as if drawn with pen, ink and ruler. The
greater distance has caused the irregularities, seen when nearer at hand,
to disappear. In this, and not in any gigantic engineering works, is the
explanation of the artificiality of the markings on Mars as Prof. Lowell
sees them. That artificiality has already disappeared under better seeing
with more powerful telescopes.
This chapter is entitled "The Illusions of Mars." Yet the illusions of
Mars are not the straight lines and round dots of the canal system, but
the forced and curious interpretation which has been put upon them. If the
planet be within a certain range of distance and under examination with a
certain telescopic power, the straight lines and round dots are
inevitable. Their artificiality is not a function of the actual Martian
details themselves, but of the mode in which, under given conditions, we
are obliged to see them.