Page:Philosophical Transactions - Volume 054.pdf/209

 whereas the latter increases it to near to near 10″ $1⁄2$: the difference is too considerable not to deserve an enquiry into its causes. The expected volume is at last come to hand; and my first care has been to examine with the most scrupulous attention the observation made at the Cape. I owe this testimony to truth, that this observation, as well as all the others of Mess. Mason and Dixon, appears to me to have been made with great judgment. An exception might however be made as to the extensive description of an appulse of σ Sagittarii to the Moon’s southern limb, which is found page 389. This certainty was more than an appulse, and the star was really immerged at the Cape.

In this same volume, I found two observations, which would be decesive, if time and other circumstances had permitted them to be made with sufficient accuracy. I have very carefully calculated them both. Mr. Maskeline observed at the island of St. Helena, situated at 15$d$ 55′ South latitude, and according to Dr. Halley at 33′ 17″ of time West of the Observatory at Paris; but this determination of the longitude does not seem sufficiently exact. I have compared many observations of Jupiter's Satellite's immersions and emersions made at the island of St. Helena by Mr. Maskeline with the corresponding ones made at Paris at the Marine Observatory by Mr. Messier, and have only found 31′ 56″ for the difference of longitude between the two places; and as the Marine Observatory is 2″ East of the Royal Observatory, I think I may conclude that the place where Mr. Maskeline observed is only at 31′ 54″ West of the Royal Observatory. LIV.