The Planet Mars
by Mentore Maggini
from Chapter II (p. 23):
We consider the greater distance at which the planet circulates from the Sun, therefore consider that its year must be longer of ours; more precisely, the Martian calendar year is made up of 668.6 solar days. The calendar of that planet is made up therefore of two years of 668 days and a leap year of 669 days; therefore: days of duration similar to ours, but years of nearly double duration.
The work of composing a tentative calendar for Mars has been undertaken most of all by the American astronomers Douglass and Pickering; they have created a calendar that, under some aspects, is similar to ours: the first nine are composed of 12 months of which contain 56 days and last the three 55 days; 7 days form one week, 8 weeks a month. The worth of this calendar is of having fixed the dates of the solstices and the equinoxes, as you can see below:
This produces a curious impression seeing, as an example, the date 36 September, which in our calendar does not exist, but that derivation having formed the months of 56 or 55 days. These dates of the Martian calendar are frequently used by observatories, especially by Pickering, and hold the place of the position that occupies the planet in its orbit.