1. Newcomb Simon, Popular astronomy (New York, 1884), 171–2. The Naval Observatory and others nevertheless sponsored many transit of Mercury observations, not for the determination of the astronomical unit, but for comparing the theory of Mercury's orbit with observation. See Washington observations for 1876 (Washington, 1879), Publications of the U.S. Naval Observatory, vi (Washington, 1911), App. 2, and idem, xv/2 (Washington,1942).