A. Tille, however (Yule and Christmas, 1899), while admitting that the general Aryan division of the year was dual, follows Tacitus in asserting that the Germanic division of the year (like the Egyptian) was tripartite: winter, spring, and summer.
Grimm, Teutonic Mythology (English translation by Stallybrass), pp. 612-630, 779, 788.
Wellhausen, Reste Arabischen Heidentums, 1897, p. 98.