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About 23h. 30m., near the close of the first day, I again inspected the barycrite. It showed 1/1100 of terrestrial gravity, an incredibly small change from the 1/800 recorded at 19h., since it implied a progress proportionate only to the square root of the difference. The observation indicated, if the instrument could be trusted, an advance of only 18,000 miles.
On December 28, 1789, the southern horn of the crescent Venus was seen truncated, an outlying lucid point interrupting the darkness beyond. Precisely the same appearance recurred two years later, giving for the planet's rotation a period of 23h. 21m.
Cassini gave the rotation as twenty-three hours, by observing a bright spot on her surface. Shroter made it 23h. 21m. 19s. This value was supported by others. In 1890 Schiaparelli announced that Venus rotates, like our moon, once in one of her revolutions, and always directs the same face to the sun.
If in the whole range of Western astronomical science there is any one fact that he has accepted as absolutely proved, it is that Mercury revolves once in 24h., 5m., 30.5s., and Venus once in 23h., 21m., 22s.
Schröter's final result in 1811 was 23h. 21m. 7·977s. Monat. Not., vol. lvii., p. 402; Astr. Phys. Roy. Astr. Nach., No. 2,021; Am. Spettr. Ital., Dicembre, 1882; Am. Ass., 1873, p. 407. Nach., No. 2,809; f. Nach., No. 3,097; Phil. Trans., vol. clxxxvi., A., p. 469; Proc. Roy. Geol. Soc., vol. iii. Mag., vol. xxviii. Wien, Bd. lxiv.; quoted by Poynting. Cf. The Moon, by T. Gwyn Elger, p. 20.
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