IN the year 1610 Galileo, looking through his telescope then
newly perfected by his own hands, discovered that the planet
Jupiter was attended by a train of tiny stars which went round
and round him just as the moon goes round the Earth.
It was a revelation too great to be credited by mankind. It was
opposed to the doctrine of the centrality of the Earth, for it
suggested that other worlds constituted like ours might exist in
the heavens.
Some said it was a mere optic illusion; others that he who looked
through such a tube did it at the peril of his soul--it was but a
delusion of Satan. Galileo converted a few of the unbelievers who
had the courage to look through his telescope. To the others he
said, he hoped they would see those moons on their way to heaven.
Old as this story is it has never lost its pathos or its
teaching.
The spirit which assailed Galileo's discoveries and which finally
was potent to overshadow his declining years, closed in former
days the mouths of those who asked the question written at the
head of this lecture: "Are we to believe that there are other
minds than ours?"
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Today we consider the question in a very different spirit. Few
would regard it as either foolish or improper. Its intense
interest would be admitted by all, and but for the limitations
closing our way on every side it would, doubtless, attract the
most earnest investigation. Even on the mere balance of judgment
between the probable and the improbable, we have little to go on.
We know nothing definitely as to the conditions under which life
may originate: whether these are such as to be rare almost to
impossibility, or common almost to certainty. Only within narrow
limits of temperature and in presence of certain of the elements,
can life like ours exist, and outside these conditions life, if
such there be, must be different from ours. Once originated it is
so constituted as to assail the energies around it and to advance
from less to greater. Do we know more than these vague facts?
Yes, we have in our experience one other fact and one involving
much.
We know that our world is very old; that life has been for many
millions of years upon it; and that Man as a thinking being is
but of yesterday. Here is then a condition to be fulfilled. To
every world is physically assigned a limit to the period during
which it is habitable according to our knowledge of life and its
necessities. This limit passed and rationality missed, the chance
for that world is gone for ever, and other minds than ours
assuredly will not from it contemplate the universe. Looking at
our own world we see that the tree of life has,
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indeed, branched, leaved and, possibly, budded many times; it
never bloomed but once.
All difficulties dissolve and speculations become needless under
one condition only: that in which rationality may be inferred
directly or indirectly by our observations on some sister world
in space, This is just the evidence which in recent years has
been claimed as derived from a study of the surface of Mars. To
that planet our hope of such evidence is restricted. Our survey
in all other directions is barred by insurmountable difficulties.
Unless some meteoric record reached our Earth, revelationary of
intelligence on a perished world, our only hope of obtaining such
evidence rests on the observation of Mars' surface features. To
this subject we confine our attention in what follows.
The observations made during recent years upon the surface
features of Mars have, excusably enough, given rise to
sensational reports. We must consider under what circumstances
these observations have been made.
Mars comes into particularly favourable conditions for
observation every fifteen years. It is true that every two years
and two months we overtake him in his orbit and he is then in
"opposition." That is, the Earth is between him and the sun: he
is therefore in the opposite part of the heavens to the sun. Now
Mars' orbit is very excentric, sometimes he is 139 million miles
from the sun, and sometimes he as as much as 154 million miles
from the sun. The Earth's orbit is, by comparison, almost
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a circle. Evidently if we pass him when he is nearest to the sun
we see him at his best; not only because he is then nearest to
us, but because he is then also most brightly lit. In such
favourable oppositions we are within 35 million miles of him; if
Mars was in aphelion we would pass him at a distance of 61
million miles. Opposition occurs under the most favourable
circumstances every fifteen years. There was one in 1862, another
in 1877, one in 1892, and so on.
When Mars is 35 million miles off and we apply a telescope
magnifying 1,000 diameters, we see him as if placed 35,000 miles
off. This would be seven times nearer than we see the moon with
the naked eye. As Mars has a diameter about twice as great as
that of the moon, at such a distance he would look fourteen times
the diameter of the moon. Granting favourable conditions of
atmosphere much should be seen.
But these are just the conditions of atmosphere of which most of
the European observatories cannot boast. It is to the honour of
Schiaparelli, of Milan, that under comparatively unfavourable
conditions and with a small instrument, he so far outstripped his
contemporaries in the observation of the features of Mars that
those contemporaries received much of his early discoveries with
scepticism. Light and dark outlines and patches on the planet's
surface had indeed been mapped by others, and even a couple of
the canals sighted; but at the opposition of 1877 Schiaparelli
first mapped any considerable
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number of the celebrated "canals" and showed that these
constituted an extraordinary and characteristic feature of the
planet's geography. He called them "canali," meaning thereby
"channels." It is remarkable indeed that a mistranslation appears
really responsible for the initiation of the idea that these
features are canals.
In 1882 Schiaparelli startled the astronomical world by declaring
that he saw some of the canals double--that is appearing as two
parallel lines. As these lines span the planet's surface for
distances of many thousands of miles the announcement naturally
gave rise to much surprise and, as I have said, to much
scepticism. But he resolutely stuck to his statement. Here is his
map of 1882. It is sufficiently startling.
In 1892 he drew a new map. It adds a little to the former map,
but the doubling was not so well seen. It is just the strangest
feature about this doubling that at times it is conspicuous, at
times invisible. A line which is distinctly seen as a single line
at one time, a few weeks later will appear distinctly to consist
of two parallel lines; like railway tracks, but tracks perhaps
200 miles apart and up to 3,000 or even 4,000 miles in length.
Many speculations were, of course, made to account for the origin
of such features. No known surface peculiarity on the Earth or
moon at all resembles these features. The moon's surface as you
know is cracked and
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streaked. But the cracks are what we generally find cracks to
be--either aimless, wandering lines, or, if radiating from a
centre, then lines which contract in width as they leave the
point of rupture. Where will we find cracks accurately parallel
to one another sweeping round a planet's face with steady
curvature for, 4,000 miles, and crossing each other as if quite
unhampered by one another's presence? If the phenomenon on Mars
be due to cracks they imply a uniformity in thickness and
strength of crust, a homogeneity, quite beyond all anticipation.
We will afterwards see that the course of the lines is itself
further opposed to the theory that haphazard cracking of the
crust of the planet is responsible for the lines. It was also
suggested that the surface of the planet was covered with ice and
that these were cracks in the ice. This theory has even greater
difficulties than the last to contend with. Rivers have been
suggested. A glance at our own maps at once disposes of this
hypothesis. Rivers wander just as cracks do and parallel rivers
like parallel cracks are unknown.
In time the many suggestions were put aside. One only remained.
That the lines are actually the work of intelligence; actually
are canals, artificially made, constructed for irrigation
purposes on a scale of which we can hardly form any conception
based on our own earthly engineering structures.
During the opposition of 1894, Percival Lowell, along with A. E.
Douglass, and W. H. Pickering,
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observed the planet from the summit of a mountain in Arizona,
using an 18-inch refracting telescope and every resource of
delicate measurement and spectroscopy. So superb a climate
favoured them that for ten months the planet was kept under
continual observation. Over 900 drawings were made and not only
were Schiaparelli's channels confirmed, but they added 116 to his
79, on that portion of the planet visible at that opposition.
They made the further important discovery that the lines do not
stop short at the dark regions of the planet's surface, as
hitherto believed, but go right on in many cases; the curvature
of the lines being unaltered.
Lowell is an uncompromising advocate of the "canal" theory. If
his arguments are correct we have at once an answer to our
question, "Are there other minds than ours?"
We must consider a moment Lowell's arguments; not that it is my
intention to combat them. You must form your own conclusions. I
shall lay before you another and, as I venture to think, more
adequate hypothesis in explanation of the channels of
Schiaparelli. We learn, however, much from Lowell's book--it is
full of interest.[1]
Lowell lays a deep foundation. He begins by showing that Mars has
an atmosphere. This must be granted him till some counter
observations are made.
[1] _Mars_, by Percival Lowell (Longmans, Green & Co.), 1896,
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It is generally accepted. What that atmosphere is, is another
matter. He certainly has made out a good case for the presence of
water as one of its constituents,
It was long known that Mars possessed white regions at his poles,
just as our Earth does. The waning of these polar snows--if indeed
they are such--with the advance of the Martian summer, had often
been observed. Lowell plots day by day this waning. It is evident
from his observations that the snowfall must be light indeed. We
see in his map the south pole turned towards us. Mars in
perihelion always turns his south pole towards the sun and
therefore towards the Earth. We see that between the dates June
3rd to August 3rd--or in two months--the polar snow had almost
completely vanished. This denotes a very scanty covering. It must
be remembered that Mars even when nearest to the sun receives but
half our supply of solar heat and light.
But other evidence exists to show that Mars probably possesses
but little water upon his surface. The dark places are not
water-covered, although they have been named as if they were,
indeed, seas and lakes. Various phenomena show this. The canals
show it. It would never do to imagine canals crossing the seas.
No great rivers are visible. There is a striking absence of
clouds. The atmosphere of Mars seems as serene as that of Venus
appears to be cloudy. Mists and clouds, however, sometime appear
to veil his face and add to the difficulty of
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making observations near the limb of the planet. Lowell concludes
it must be a calm and serene atmosphere; probably only
one-seventh of our own in density. The normal height of the
barometer in Mars would then be but four and a half inches. This
is a pressure far less than exists on the top of the highest
terrestrial mountain. A mountain here must have an altitude of
about ten miles to possess so low a pressure on its summit. Drops
of water big enough to form rain can hardly collect in such a
rarefied atmosphere. Moisture will fall as dew or frost upon the
ground. The days will be hot owing to the unimpeded solar
radiation; the nights bitterly cold owing to the free radiation
into space.
We may add that in such a climate the frost will descend
principally upon the high ground at night time and in the
advancing day it will melt. The freer radiation brings about this
phenomenon among our own mountains in clear and calm weather.
With the progressive melting of the snow upon the pole Lowell
connected many phenomena upon the planet's surface of much
interest. The dark spaces appear to grow darker and more
greenish. The canals begin to show themselves and reveal their
double nature. All this suggests that the moisture liberated by
the melting of the polar snow with the advancing year, is
carrying vitality and springtime over the surface of the planet.
But how is the water conveyed?