| -20 | +95 || +39 || -202 | -217 | -172 | -136 | | 235 | 342 || 290 || 66 | 52 | 94 | 127 | | -38 | +69 || +17 || -207 | -221 | -179 | -146 | | 337 | 486 || 412 || 94 | 74 | 133 | 180 | | +64 | +213 || +139 || -179 | -199 | -140 | -93 | | 300 | 438 || 371 || 84 | 67 | 120 | 162 | | +27 | +165 || +98 || -189 | -206 | -153 | -111 | | | || || | | | | +--------+--------++--------++---------+---------+--------+---------+ For in regard to this particular premiss we can do away with hypothesis, and deal only with certain physical facts that are not controversial and are not in dispute. The first of this series of facts concerning Mars about which there can be no controversy or dispute relates to its size and mass. As the foregoing Table shows, it comes between the Moon and the Earth in these respects. The figures show at a glance that Mars ranks in its dimensions between the Moon and the Earth, and that, on the whole, it is more like to the Moon than it is to the Earth. But in what way would this affect Mars as a suitable home for life? In many ways; and amongst these the distribution of its atmosphere and the sluggishness of its atmospheric circulation are not the least important. It was mentioned in Chapter III that at a height of about three and a third miles the barometer will stand at 15 inches, or half its mean height at sea level, showing that one half the atmosphere has been passed through. Mont Blanc, the highest mountain in Europe, is under 3 miles in height, so that it is not possible, in Europe, to climb to the level of half-pressure; Mt. Everest, the highest mountain in the world, is not quite six miles high, so that no part of the solid substance of our planet reaches up to the level of the quarter pressure. On a very few occasions daring aeronauts have soared into the empyrean higher than the summits of even our loftiest mountains, but the excursion has been a dangerous 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 this height the rarefaction of the air was so great and the cold so intense that Mr. Glaisher fainted, and Mr.