Note 37 — Chapter IX · MARS.

Herschel’s earlier observations were made in 1777-79, and his period, like that of his predecessors, is about 2 min. in excess of the correct value; but Mädler pointed out that, by giving Mars an additional rotation on his axis, Herschel’s value will agree within 2 sec. of his own. Herschel appears to have adopted 768 rotations instead of 769, and may have been led to this by the excessive periods of Cassini and Maraldi and by the want of intermediate data between his own observations in April 1777 and May-June 1779. His second determination, made in 1784, is more correct.