by Percival Lowell
edited by Thomas Gangale
from Chapter IIAtmosphere:
I. Evidence of it
From early in June, which corresponded to the Martian last of April, to the end of November, which corresponded to the Martian last of August, the bluish-green areas underwent a marked transformation.
from Chapter 3Water:
I. The Polar Cap
On the 3d of June, 1894, the south polar cap stretched, almost one unbroken waste of white, over about 55 degrees of latitude. A degree on Mars measures 37 miles; consequently the cap was 2,035 miles across. Inasmuch as the inclination of the Martian equator to the plane of the Martian orbit is, according to Schiaparelli, 24° 52', it must have then covered more than the whole south frigid zone of the planet.
Now, to take in the full meaning of the condition of the cap at this time and of the changes that ensued, we must begin by determining the Martian time of year. This is done by fixing the dates at which the Martian pole reached its maximum tilt toward or from the Sun, and the dates at which it was not tilted either to or from, but sideways to, the Sun; the former gives us the Martian solstices, and the latter the Martian equinoxes. It thus appears that on April 7, 1894, occurred the vernal equinox of the Martian southern hemisphere, on August 31, its summer solstice, and on February 7, 1895, its autumnal equinox. From these dates it is easy to transform the one calendar into the other. On the 3d of June, 1894, therefore, it was about May 1 on the southern hemisphere of Mars.
On May 1, then, Martian time, the cap was already in rapid process of melting; and the speed with which it proceeded to dwindle showed that hundreds of square miles of it were disappearing daily.
On examining the chart in which the successive appearances of the southern ice-cap are depicted at different times, from June 3 to October 13, or, in terms of the Martian time of year, from May 1 to July 15, the first point to strike one is that the cap was during its whole existence eccentrically placed with regard to the geographical pole of the planet.
On October 12, at 10h. 40m., I made the following entry about it: "Polar cap has been very faint for some time; barely visible." At 13h. 26m., or, in other words, at about half past one that night, Mr. Douglass measured its position and estimated its size, as was his wont every few days. He found it to be six degrees distant from the planet's pole, in longitude 54 degrees The patch was very small, covering about one hundred and fifty miles square. On looking at the planet on October 13, at 8h. 15m., to his surprise he found the cap gone. Not a trace of it could be seen; nor could either he or I detect it during the rest of that night although such was the longitude of the central meridian throughout it as to bring the cap on the nearer side of the pole, and therefore show it to best advantage. What had certainly been there on the 12th was not there on the 13th. The ice-cap had disappeared.
No such occurrence has ever been chronicled before. It is the first time since man began to observe the planet that the ice-cap has completely disappeared. Hitherto it has been seen to diminish to a minimum of from 7 to 4 degrees, and then begin to increase again. This last autumn, for the first time, it vanished entirely. The date of this occurrence was, in Martian chronology, about July 20. Evidently, for some reason unknown to us, it was a phenomenally hot season in the southern hemisphere of the planet.
For an appreciation of the meaning of the changes, it is to be borne in mind throughout that the vernal equinox of Mars' southern hemisphere occurred on April 7, 1894; the summer solstice of the same hemisphere on August 31; and its autumnal equinox on February 7, 1895.
On the 31st of May, therefore, it was toward the end of April on Mars.
from Chapter VOases:
I. Spots in the light regions
By November, the Phoenix Lake had become less salient, Ceraunius relatively more so, and the Cyane Fons nearly as evident as Ceraunius had formerly been. In the Martian calendar, the August observation corresponded to our 20th of June, the November one to our 1st of August.