The northern and southern portions of the mare did not behave alike in taking on the chocolate tint. From the notes made about them during the opposition it appears that the latter was later than the former in undergoing the metamorphosis, as will be seen from the following depth of the blue green estimated in percentages shown at different dates, calling the deepest tone ever exhibited by it unity.
| Martian Date, | December (16) | January (1) | January (17) | February (5) | February (24) |
| % | % | % | % | % | |
| Northern | 50 | 50 | 0 | 25 | 50 |
| Southern | 50 | 50 | 0 | 0 | 25 |
From this table we may place the lowest point of the blue-green tint as reached about the 22d of January for the northern, the 5th of February for the southern, part. This would indicate that the wave of returning growth came from the north, not the south; an important fact, as we shall see later in studying the action of the canals.
Mare Erythræum
Martian date. February 1
At the next opposition, in 1905, a recurrence of the transformation was watched for, and not in vain. It occurred, however, somewhat later in the Martian season. On December 27 of the planet’s current year the Mare Erythraeum was still as usual, blue-green, nothing out of the ordinary being remarked in it; and so it was on its January 17, although the southern edge was darker than the northern. It looked certainly as if the metamorphosis were this year to be omitted. But such was not the case. When the region again came round, on February 1 of the Martian calendar, there the strange tint was as unmistakable as it had been on its original occurrence. Not only was the Mare Erythraeum so colored, but on February 5 (Martian) the northern portion of the Mare Cimmerium was observed to be similarly affected. In the Mare Erythraeum the anomalous chocolate hue was confined to a belt between the latitudes of 10° and 20° south of the equator; in the Mare Cimmerium it stretched a little higher, from 10° at the west to 25° at the east. It is noteworthy that the southern portion of the latter showed blue at the time the northern showed brown. Then the metamorphosis proceeded as shown in the following table:—
Mare Erythraeum 1905
| Mundane Date | Days after Winter Solstice of Southern Hemisphere | Martian Date | Aspect |
| January 25 | 12 | December 27 | Blue-green |
| March 6 | 52 | January 16 | Blue-green |
| April 4 | 81 | January 31 | Chocolate |
| April 12 | 89 | February 4 | Chocolate |
| April 30 | 107 | February 13 | Faint chocolate |
| May 8 | 115 | February 17 | Faint chocolate |
| May 12 | 119 | February 19 | Faint blue-green |
| June 11 | 149 | March 6 | Faint blue-green |
| June 15 | 153 | March 8 | Faint blue-green |
| July 16 | 184 | March 23 | Pale bluish green |
Here, as in 1903, a chromatic rise and fall is evident; the culmination of the change occurring in Martian early February about ninety days after the winter solstice. That it was not of long duration is also indicated. If we examine the evidence for the two portions of the mare separately, the northern and the southern, as in 1903, we find it as follows:—
| Martian Date, | December (27) | January (16) | February (2) | February (16) | March (7) | March (23) |
| % | % | % | % | % | % | |
| Northern | 50 | 50 | 0 | 10 | 25 | 30 |
| Southern | 50 | 50 | 20 | 20 | 25 | 30 |