Are the Planets Inhabited?

osing views join issue; the controversy comes to a focus. The point in debate i

out deviation or break, as if drawn with pen, ink, and compass; if, moreover, when we obtain more powerful telescopes, erected in better clima

then, the "lines" and "circles" that Prof. Lowell and his disciples assert to be artificial canals and oases are really such, they premise the order of being that we call Man. But these canals and oases also premise the liquid that we c

72 &

ARY ST

i

er Planets.

rs Venus Earth Uranus

ns of the

163 3030 4230 7700 7918

83 0·534 0·972 1·000 4

075 0·147 0·285 0·945 1

0·02 0·06 0·15 0·92 1

? 3·39 4·72 3·92 4·94 5

0·85 0·71 0·89 1·00

2 0·048 0·107 0·820 1·

0·028 0·17 0·33 0·38 0·8

Second 0·45 2·73 5·30 6·11 13·

14 0·22 0·76 0·50 ?

s of O

s of miles 257·1 92·9 36·0 141·5

67 1·000 0·387 1·524 0·723 1

rs 4·60 1·00 0·24 1·88 0·62

econd 11·1 18·5 9·7 15·0

0·2056 0·0933 0·0068 0·0168

1 1·157 1·034 1·517 1·207 1·01

it (?) 1°·32′ (?) 24°·0′ (?)

m s h m s

3 88(?) 24·37·23 (?) 23·56

ing the total mas

nal to the mass

per sq. inch. 0·014 0·40 1·6 2·

009 0·027 0·108 0·143 0·75

ure in miles 119·0 19·6 10·

e surface 22°C 53°C 53°C 92°

erat

n, ⊕ = 1 0·13 1·00 6·67 0·43 1·

stance, ⊕ = 1 0·60 1·00 1·61 0·

net, Absolute 188 312° 502° 2

5 +39 +229 -20 +95 +3

anet, Absolute 174 290 46

9 +17 +194 -38 +69 +1

sun, Absolute 248 412 664

5 +139 +391 +64 +213

t disc, Absolute 223 371 5

0 +98 +325 +27 +165 +

with hypothesis, and deal only with certain physical f

e no controversy or dispute relates to its size and mass. As the foregoin

sions between the Moon and the Earth, and that, on the wh

many ways; and amongst these the distribution of its atmosphere and the

one, and they have with difficulty brought their life back from so rare and cold, so inhospitable a region. When Gay-Lussac, in 1804, attained a height of 23,000 feet above sea level, the thermometer, which on the ground read 31° C., sank to 9° below zero, and the rare atmosphere was so dry that paper crumpled up as if it had been placed near the fire, and his pulse rose to 120 pulsations a minute instead of his normal 66. When Mr. Glaisher and Mr. Coxwell made their celebrated ascent between 1 and 2 o'clock on the afternoon of September 5, 1861, they found that at a height of 21,000 feet the temperature sank to -10·4°; at 26,000 feet to -15·2°; and at 39,000 feet the temperature was down to -16·0° C. At thi

use of precipitation here is much weakened there. A current of air heavily laden with moisture, if it encounters a range of mountains, is forced upwards, and consequently expands, owing to the diminished pressure. The expansion brings about a cooling, and from both causes the atmosphere is unable to retain as much water-vapour as it carried before. On Mars, the same relative expansion and cooling would only follow if the ascent were nearly three times as

luggish, and precipitation is sli

d valley o

t hail, or rai

wind blow

mistake when he referred to Mars as being "hurricane-swept." There are no hurricanes on M

tively feeble. The greater the force of gravity the more active the atmospheric circulation, and more violent its d

of a second of arc, at an average opposition. The oases, as a rule, are about 120 miles in diameter, that is to say about half a second of arc. These are extraordinarily fine details to be perceived and held, even if Mars had no atmosphere at all; it would certainly be impossible to detect them unless the atmosphere were exceedingly thin and transparent. For we must remember that, though our own atmosphere is a hindrance to our observing, yet t

ere proportional to its mass, then we see from the Table that this must be a little less than 1?9th of that of the Earth; exactly 0·107. It is distributed over a smaller surface, 0·285. Consequently the amount of air above each square inch of Martian surface is 0·107 ÷ 0·285 = 0·38. But since the force of gravity at the surface of Mars is less than on the Earth, this column of air will only weigh 0·38 × 0·38 = 0·145; or one-seventh of the column of air resting on a square inch of the E

re inch; that is, of half the terrestrial surface pressure. Plant life dies out before we reach that point, and though birds or men may occasionally attain greater heights, they cannot domicile there, and are, indeed, only able thus to ascend in virtue of nourishment which they have procured in more favoured regions. If we could suppose the conditions of t

degrees it remains in a liquid condition. On Mars, under the assumed conditions, water would boil at 53° C., and the range of temperatu

the lighter, most swiftly moving molecules must occasionally be moving directly outwards from the planet at the top of their speed, and in this case, if the speed of recession should exceed that which the gravity of the planet can control, the pa

ing the albedo of the Earth itself, and Mr. Lowell puts it higher than most astronomers would do; then there is the difficulty of determining what portion of the total albedo is to be referred to the atmosphere and what to the actual soil or surface of the planet. But, on the whole, Mr. Lowell concludes that the amount of atmosphere above the unit of surface of Mars is 0·222 of that abo

have a little less ground to walk upon on Mars, and a good deal more on Jupiter. Dean Swift, in Gulliver's Travels, made the Lilliputians take a truer view of the effect of the alteration of one dimension, for, finding that Gulliver was twelve times as tall as the average Lilliputian, they did not appoint him the rations of twelve Lilliputians, which would have been rather poor feeding for that veracious mariner, but allotted him the cube of twelve, viz. seventeen hundred and twenty-eight rations. Mr. J. Holt Schooling, in one of his ingenious and interesting statistical papers, tried to bring home the vast extent of the British Empire by supposing that it seceded, and taking the portion of Earth that has fallen to it, set up a world of its own-the planet "Victoria." He allots to the British Empire 21 per cent of the land surface of

the cube; everywhere the smaller planet must have the rarer atmosphere, and with a rare atmosphere the extreme range of temperature must be great, while the range of temperature within which water will flow w

at the Earth does. But, as the Table shows, from its greater distance from the Sun, Mars receives

ions. The length of the day is also nearly the same for both, the Martian day being slightly longer; but the most serious factor is the greater distance of Mars, and the consequent diminution in the light and heat received from the Sun.

e zero of the Centigrade scale is not the absolute zero; it only marks the freezing-point of water. The absolute zero is computed to be -273° on the Centigrade scale; the temperature of the Earth on the absolu

perature; so that if Mars were at 124° abs., while the Earth were at 289° abs., the Earth would be radiating its heat nearly 30 times faster than Mars. The heat income of Mars would therefore be in a much higher proportion than its expenditure; and necessarily its heat capital

as resembling our Moon, and take the Moon's effective average temperature as 297° abs., the corresponding temperature for Mars is 240° abs., and the highest temperature is four-fifths of 337° = 270° abs. But the surface of Mars has probably a higher coefficient of absorption than the surface of the Moon-it certainly has for light-so that we may put his effective average temperature, on this supposition, some few degrees above 240° abs., and his equatorial temperature some degrees higher still. It appears as exceeding

s zenith, and is fully presented to its light and heat. But, as we move away from the equator, we find that each higher latitude is less fully presented to the Sun, until, when we reach latitude 64?°-in other words just outside the Arctic Circle-7 square yards are presented to the Sun

moving polewards, carrying with them vast stores of heat to be liberated as the rain falls. The oceanic currents have the same effect, and how great the modification which they introduce may be seen by comparing the climates of Labrador and Scotland. There appear to be no great oceans on Mars. The difference of 28° which we find on the Earth between the equator and the edge of the Arctic Circle is a difference which remains after the convection currents of air and sea have done much to reduce the temperature of the equator and

ot look like a cold planet. As we look at it, and note its bright colour, the small extent of the white caps presumed to be snow, and the high latitudes in which the dark markings-presumed to be water or vegetation-are seen, it seems difficult to suppose that the mean temperature of the planet is lower than that of the Earth. Thus on the wonderful photographs taken by Prof. Barnard in 1909, the Nilosyrtis with the Protonilus is seen as a dark canal. Now the Protonilus is in North Lat. 42°

rom this curve ordinates have been drawn at each 10°, upward to show average deviation from the mean temperature for the hottest part of the day in summer, downward for the deviation for the coldest part of the night in winter. Obviously, on the average, the range from maximum to minimum will increase from the equator to the poles. The mean temperature of the Ear

er I

s of the Ea

the temperatures of different latitudes cannot be equalized to the same extent as on the Earth. It follows, therefore, that the range in mean temperature from equator to pole must be considerably greater on Mars than on the Earth. Thirdly, the range in temperat

n any given latitude more pronounced than upon the Earth. And the general lesson of the diagram may be summed up in a sentence. The maximum temperature on the planet is well above freezing-point, and the part of the planet at maximum temperature is precisely the part that we see

t hours of the Martian day. Every night will be for it a winter, a winter of undescribable frost, which it could only endure in the form of spores. So if there be vegetation it must be confined to some hardy forms of a low type. At a distance of forty millions of miles it is not easy to discriminate between the darkness of sheets of water and the dar

ch day.... There is no evidence that snow like ours ever forms around the poles of Mars. It does not seem possible that any considerable fall of such snow could ever take place, nor is there any necessity of supposing actual snow or ice to account for the white caps. At a temperature vastly below any ever felt in Siberia, the smallest particles of moisture will be condensed into what we call hoar frost, and will glisten with as much whiteness as actual s

nd cloud shows the atmosphere to be rare and the moisture little in amount and readily evaporated. The seas are probably shallow depressions, filled with ice to the bottom, but melted as to their surfaces by day. From the variety of