MARS AND ITS CANALS
By the early spring of 1901 Percival was well over his illness, and fit
to return to the Observatory for the oppositions of Mars in that year,
in 1903 and in 1905. Shortly after he came back the services of Mr.
Douglass came to an end, and he was fortunate in obtaining Dr. V. M.
Slipher in 1901 and Mr. C. O. Lampland in the following year—two young
men who were not only invaluable assistants to him, but during his
lifetime, and ever since, have made distinguished contributions to
science. Observing at all hours of the night was exacting work; and to
anyone less enthusiastic, who did not see through the detail to its
object, it might have been monotonous and wearisome. As he wrote
himself, “Patient plodding is the road to results in science, and the
shortest road in the end. Each year out here has seemed to me the best,
which merely means that I hope I learn a little and that there is a vast
deal to learn.” He felt strongly the need of diligence and strict
impartiality in ascertaining the facts, and distinguished it sharply
from the imagination to be used in interpreting them. In describing his
delineation of the canals he says, “Each drawing, it should be
remembered, was as nearly an instantaneous picture of the disk as
possible. It covered only a few minutes of observation, and was made
practically as if the observer had never seen the planet before. In
other words, the man was sunk in the manner. Such mental effacement is
as vital to good observation as mental assertion is afterward to
pregnant reasoning. For a man should be a machine in collecting his
data, a mind in coördinating them. To reverse the process, as is
sometimes done, is not conducive to science.” But through all the
exacting labor of the search he felt keenly the joy of discovery,
comparing himself to the explorers of the Earth, and in the first
chapter of “Mars and its Canals” he tells us of the pleasure of a winter
night spent in the Observatory.
The oppositions in 1901, 1903 and 1905 were not so favorable as those of
1894 and 1906-1907, because Mars was not so near the Earth; the
eccentricities in the orbits of the two planets causing them to pass
each other when Mars was far from the Sun and therefore from the Earth
whose eccentricity is less. Yet they had an advantage in the fact that,
unlike the earlier occasions, the south pole was tipped away from the
Earth, and the north pole was toward it, thus giving a good view of the
northern polar cap, sub-arctic and higher temperate zones, which had not
been visible before. Thus the seasonal changes could be observed in the
opposite hemisphere,—not an inconsiderable gain, because the dark and
light areas, that is, the natural vegetation and the deserts, are not
equally distributed over the planet, for the dark ones occupy a much
larger part of the southern, and the deserts of the northern,
hemisphere. Moreover, the use of a larger lens and better atmosphere had
shown that observations could be carried on profitably for a longer
period before and after the actual opposition; until in 1905 it was
possible to cover what had been left unobserved of the Martian year in
the northern half of Mars.
No sooner was the third of these oppositions past than he wrote another
book on the subject, with the title “Mars and its Canals”; and this in
no sense a supplement to the earlier one, but an entirely new and
independent presentation of the subject, covering the old ground and
much more. He was enabled to do this because the copyright of the
earlier work belonged to him. The later one was published by The
Macmillan Company in December 1906, and dedicated to Schiaparelli. Like
the earlier book, he wrote it by no means for astronomers alone, but for
the interested public; and in the preface he tells why he did so: “To
set forth science in a popular, that is in a generally understandable,
form is as obligatory as to present it in a more technical manner. If
men are to benefit by it, it must be expressed to their comprehension.
To do this should be feasible for him who is master of his subject, and
is both the best test of, and the best training to that post.... Nor is
it so hard to make any well-grasped matter comprehensible to a man of
good general intelligence as is commonly supposed. The whole object of
science is to synthesize, and so simplify; and did we but know the
uttermost of a subject we could make it singularly clear.” At the same
time there was nothing in these writings of the nature of what is
commonly called popularizing science. He expounded his subject in a
strictly scientific way, but avoided unfamiliar technical terms if
possible, and sought to raise his readers or audience to his level of
thought, not to descend to theirs. Such statements for the public were
very often preceded by technical ones in the Bulletins of the
Observatory or elsewhere, and yet it cannot be doubted that the former
tended to alienate some scientific scholars who were slow to admit his
discoveries, and did not sympathize with his method of presenting them,
or perhaps with the attractive style of the man of letters as well as of
exact thought.
Still there are pitfalls in taking the public into one’s confidence; as
he found in December 1900, when a telegram sent by the usual channels to
the astronomical world, that the night before a projection had been
observed on Mars that lasted seventy minutes, was taken by the press to
mean an attempt by Martians to signal to the Earth, and as such was
proclaimed all over America and Europe. The cause of the excitement, as
he explained a year later to the American Philosophical Society in
Philadelphia, was the reflection from a cloud on the horizon of the
planet.
“Mars and its Canals” is frankly a demonstration that the planet is
habitable, and that from what takes place there it must in fact be
inhabited by highly intelligent beings. For that purpose the book is
divided into four parts, entitled: Natural Features; Non-Natural (that
is, artificial) Features; The Canals in Action; and Explanation. His
general thesis, which he was to expound more fully later (and which
although not essential to his argument for life on Mars he connected
therewith) was that all planets go through the same process of
development—varying, however, with their size which determines their
power to retain the gases of their atmosphere—and that one element
therein is the gradual leakage of water through cracks into its interior
as the planet cools. He cites geologists to prove that the oceans
formerly covered much more of the surface of the Earth than they do now;
argues that the desert belts around it are of comparatively recent
geologic origin, as shown by the petrified forest of Arizona; and points
out the similarity in color, as seen from the San Francisco Peaks, of
the forested hills and the painted desert there, to that of the
blue-green and reddish-ochre spaces of Mars as presented by the
telescope. He notes also that to get water in our deserts plants and
animals have sought the higher altitudes, and are able to exist and
multiply in an air less dense and a climate cooler with a shorter warm
season than in their natural habitat, adjusting themselves to these
conditions.
This idea of the lack of water on Mars he derives from observation of
its surface and the changes thereon; for the supply of water is in great
part locked up in the snow or ice of the polar caps during the Martian
winters of the two hemispheres and distributed over its surface as
summer comes on. Therefore he naturally begins his account of the
natural features of the planet by a description of these polar snow
caps, their formation and melting. In doing so he cannot resist a
sarcastic reference to the endless enthusiasm, useless expenditure of
money and labor, and the scientific futility of arctic exploration.
“Polar expeditions exert an extreme attraction on certain minds, perhaps
because they combine the maximum of hardship with the minimum of
headway. Inconclusiveness certainly enables them to be constantly
renewed, without loss either of purpose or prestige. The fact that the
pole has never been trod by man constitutes the lodestone to such
undertakings; and that it continues to defy him only whets his endeavor
the more. Except for the demonstration of the polar drift-current
conceived of and then verified by Nansen, very little has been added by
them to our knowledge of the globe. Nor is there specific reason to
suppose that what they might add would be particularly vital. Nothing
out of the way is suspected of the pole beyond the simple fact of being
so positioned. Yet for their patent inconclusion they continue to be
sent in sublime superiority to failure.
“Martian polar expeditions, as undertaken by the astronomers, are the
antipodes of these pleasingly perilous excursions in three important
regards, which if less appealing to the gallery commend themselves to
the philosopher. They involve comparatively little hardship; they have
accomplished what they set out to do; and the knowledge they have
gleaned has proved fundamental to an understanding of the present
physical condition of the planet.”
Then follows the story of the melting of the polar snows, the darkening
of the blue-green areas by the growth of vegetation due to the flow of
water; and a summary, at the close of [Part I] (Natural Features), of
the reasons for believing that from its atmosphere, temperature, and the
actual, though scanty, supply of water, Mars is capable of supporting
life. In fact the presence of vegetation proves that life of that kind
does exist, in spite of the fact that five-eighths of the surface is
desert; and if plants can live animals might also. But, unlike
vegetation, they could not be readily seen, and save in the case of
intelligent operation on a large scale, their presence could not be
detected. This is the significance of the canals, to which much of the
observation of the last three oppositions was directed.
Close to the limit of vision, and only to be seen at moments when the
atmosphere is steady, the fainter canals are very hard to observe.
Percival describes the experience in this way:
“When a fairly acute eyed observer sets himself to scan the telescopic
disk of the planet in steady air, he will, after noting the dazzling
contour of the white polar cap and the sharp outlines of the blue-green
areas, of a sudden be made aware of a vision as of a thread stretched
somewhere from the blue-green across the orange areas of the disk. Gone
as quickly as it came, he will instinctively doubt his own eyesight, and
credit to illusion what can so unaccountably disappear. Gaze as hard as
he will, no power of his can recall it, when, with the same startling
abruptness, the thing stands before his eyes again. Convinced, after
three or four such showings, that the vision is real, he will still be
left wondering what and where it was. For so short and sudden are its
apparitions that the locating of it is dubiously hard. It is gone each
time before he has got its bearings.
“By persistent watch, however, for the best instants of definition,
backed by the knowledge of what he is to see, he will find its coming
more frequent, more certain and more detailed. At last some particularly
propitious moment will disclose its relation to well known points and
its position be assured. First one such thread and then another will
make its presence evident; and then he will note that each always
appears in place. Repetition _in situ_ will convince him that these
strange visitants are as real as the main markings, and are as permanent
as they.”
Strangely enough fine lines, from the continuity of the impression they
make upon the eye, can be recognized when of a thickness that would be
invisible in the case of a mere dot. To determine how narrow a line on
Mars would be perceptible, experiments were made with a wire of a
certain size, noting the limit of distance at which it could be seen;
and then, from the magnifying power of the telescope, it was found that
a Martian canal would be visible down to about a mile wide. From this
the conclusion was drawn that the canals probably ran from two or three
up to fifteen or twenty miles in width, the minimum being much less than
had been thought at earlier oppositions. The distance apart of the two
branches of double canals he estimated at about seventy-five to one
hundred and eighty miles, save in one case where, if a true instance of
doubling, it is over four hundred. Of the oases, whereof one hundred and
eighty-six had been observed, much the larger part were from
seventy-five to one hundred miles in diameter.
The later oppositions enabled him also to complete the topography of the
planet, showing that the canals were a vast system, running from the
borders of both polar caps, through the dark areas of natural vegetation
where they connected, at obviously convenient points, with a still more
complex network in the ochre, or desert, regions, and thus across the
equator into the corresponding system in the other hemisphere. By this
network the greater part of the canals could receive water alternately
from the melting of the north and south polar caps, or twice yearly, the
Martian year, however, being almost twice as long as our own. But to
perfect his proof that this actually takes place he had to show that the
canals, that is the streaks of vegetation bordering waterways, sprang
into life—thereby becoming visible or darker—in succession as the water
spread from the poles to the tropics; and this he did with his usual
thoroughness at the opposition of 1903.
Since there was then no mechanical means of measuring the variations in
visibility of the canals,—and under the atmospheric conditions at any
place in the world perhaps there never will be,—the record had to be
made by the eye, that is in drawings by the observer as he saw the
canals; and these, as he said, must be numerous, consecutive and
extended in time. The consecutive could not be perfectly carried out
because “as Mars takes about forty minutes longer to turn than the
Earth, such confronting (of the observer) occurs later and later each
night by about forty minutes, until finally it does not occur at all
while Mars is suitably above the horizon; then the feature passes from
sight to remain hidden till the difference of the rotations brings it
round into view again. There are thus times when a given region is
visible, times when it is not, and these succeed each other in from five
to six weeks, and are called presentations. For about a fortnight at
each presentation a region is centrally enough placed to be well seen;
for the rest of the period either ill-placed or on the other side of the
planet.” But with changes as gradual and continuous as those of the
darkening of the canals this did not prove a serious drawback to the
continuity of the record.
There was another element in the problem. The drawing being the estimate
of the observer on the comparative darkness of the markings from time to
time it was of the greatest importance to avoid any variation in
personal estimates, and therefore Percival made all the drawings
himself. From April 6 to May 26 he drew the planet every twenty-four
hours, and although “the rest of the time did not equal this perfection,
no great gap occurred, and one hundred and forty-three nights were
utilized in all.... But even this does not give an idea of the mass of
the data. For by the method employed about 100 drawings were used in the
case of each canal, and as 109 canals were examined this gave 10,900
separate determinations upon which the ultimate result depended.”
For each canal he plotted the curve of its diminishing or increasing
visibility as the season advanced, and this curve he called the
cartouche of the canal. Now combining the cartouches of all the canals
in each zone of latitude, he found that those in the several zones began
to become more distinct—that is the vegetation began to come to life—in
a regular and approximately uniform succession, taking from the northern
arctic down to the equator and past it to the southern sub-tropic about
eighty Martian days. From north latitude 72° to the equator, a distance
of 2,650 miles, took fifty-two of these days, at a speed of fifty-one
miles a day, or 2.1 miles an hour. Now all this is precisely the
opposite of what happens on the Earth, where vegetation in the spring
starts in the part of the temperate zone nearest to the equator, and as
the season advances travels toward the pole; the reason for the
difference being, he says, that what is needed on Earth to make the sap
run is the warmth of the sun, what is needed on Mars is water that comes
from the melting of the polar snows. He points out also that the water
cannot flow through the canals by nature, because on the surface of a
planet in equilibrium gravity would not draw it in any direction toward
or away from the equator. “No natural force propels it, and the
inference is forthright and inevitable that it is artificially helped to
its end. There seems to be no escape from this deduction.” In short,
since water certainly cannot flow by gravity both ways in the same
canal, the inhabitants of Mars have not only dug the canals, but pump
the water through them.
[Illustration: OBSERVING AND DRAWING THE CANALS OF MARS]
[Illustration: Drawing]
In recapitulating the reasons for the artificial character of the canals
he shows a most natural annoyance with people who doubted the validity
of his observations; and, in dealing with the evidence to be drawn from
the fact that they run on great circles, that is on the shortest lines
from one point to another, he writes: “For it is the geodetic precision
which the lines exhibit that instantly stamps them to consciousness as
artificial. The inference is so forthright as to be shared by those who
have not seen them to the extent of instant denial of their objectivity.
Drawings of them look too strange to be true. So scepticism imputes to
the draftsman their artificial fashioning, not realizing that by so
doing it bears unconscious witness to their character. For in order to
disprove the deduction it is driven to deny the fact. Now the fact can
look after itself and will be recognized in time.”
This last prophecy was largely verified before these three oppositions
of the planet came to an end. In 1901 photography was tried without
success so far as the canals were concerned. For the stars it had worked
very well, for to quote again: “Far less sensitive than the retina the
dry plate has one advantage over its rival,—its action is cumulative.
The eye sees all it can in the twentieth of a second; after that its
perception, instead of increasing, is dulled, and no amount of
application will result in adding more. With the dry plate it is the
reverse. Time works for, not against it. Within limits, themselves long,
light affects it throughout the period it stands exposed and, roughly
speaking, in direct ratio to the time elapsed. Thus the camera is able
to record stars no human eye has ever caught and to register the
structure of nebulae the eye tries to resolve in vain.
“Where illumination alone is concerned the camera reigns supreme; not so
when it comes to a question of definition. Then by its speed and agility
the eye steps into its place, for the atmosphere is not the void it
could be wished, through which the light-waves shoot at will. Pulsing
athwart it are air-waves of condensation and rarefaction that now
obstruct, now further, the passage of the ray. By the nimbleness of its
action the eye cunningly contrives to catch the good moments among the
poor and carry their message to the brain. The dry plate by its slowness
is impotent to follow. To register anything it must take the bad with
the better to a complete confusion of detail. For the air-waves throw
the image first to one place and then to another, to a blotting of
both.”
There lay the difficulty which Mr. Lampland, then new to the
Observatory, took up in 1903. The photographs, though better, still did
not show the canals. Various adjustments were then made with the
telescope; all manner of plates were tried between the rapid and the
well-defining ones; and finally in 1905 upon the plates canals appeared,
thirty-eight in all and one of them double.[16] On learning of the
success Schiaparelli wrote in wonder to Percival, “I should never have
believed it possible”; and the British Royal Photographic Society
awarded its medal to Mr. Lampland.
With the observations of 1905 ended until the next opposition of the
planet an exploration and a romance of which he wrote:
“To some people it may seem that the very strangeness of Martian life
precludes for it an appeal to human interest. To me this is but a
near-sighted view. The less the life there proves a counterpart of our
earthly state of things, the more it fires fancy and piques inquiry as
to what it be. We all have felt this impulse in our childhood as our
ancestors did before us, when they conjured goblins and spirits from the
vasty void, and if our energy continue we never cease to feel its force
through life. We but exchange, as our years increase, the romance of
fiction for the more thrilling romance of fact. As we grow older we
demand reality, but so this requisite be fulfilled the stranger the
realization the better we are pleased. Perhaps it is the more vivid
imagination of youth that enables us all then to dispense with the
hall-mark of actuality upon our cherished visions; perhaps a deeper
sense of our own oneness with nature as we get on makes us insist upon
getting the real thing. Whatever the reason be, certain it is that with
the years a narration, no matter how enthralling, takes added hold of us
for being true. But though we crave this solid foothold for our
conceptions, we yield on that account no jot or tittle of our interest
for the unexpected.”