VOL. XXX.] PHILOSOPHICAL TRANSACTIONS. 387 



which the limb in that place seemed a little protuberant. At 12^ 5"™ appeared 

 the fourth satellite just come out of the disk, and touching the limb in the 

 place where the protuberancy was. At 12^ 7^" we could perceive the satellite 

 separated from the limb. At 13^ 56"^ the second black, spot, still within the 

 disk, just touched the western limb; soon after which there appeared a notch 

 in this part of the limb, as it did on the other at the coming on of this spot. 

 At 14^ 6"^ the spot was all gone off, and the limb appeared clear and entire. 

 The first spot, when in the middle of Jupiter, was almost as black as the second 

 when near the limb, but somewhat less and a little more northerly. 



At the time that the first spot was in the middle of the disk, the three inner- 

 most satellites appeared to the east of Jupiter; the first having lately emerged 

 out of the shadow ; the second being almost at its greatest distance ; and the 

 third having passed the axis of the shadow about 12 hours before, and appearing 

 at this time about 3 diameters of Jupiter from his limb. The times that these 

 spots arrived at the middle of the disk are agreeable to the times found by cal- 

 culation, in which the fourth satellite and its shadow ought to have appeared 

 there. From all which it is plain, that the first of these spots was the fourth 

 satellite itself, and the second its shadow. 



We have seen the first and second satellites appearing not as dark spots, but 

 as bright ones, somewhat different from the light of Jupiter, for some little 

 time after they entered his disk, but as they approached nearer the middle, we 

 lost sight of them. And we have frequently observed that the same satellites 

 appear brighter at some times than at others ; and that when one of them has 

 shone with its utmost splendour, the light of another has been considerably 

 diminished. From whence it is very probable, not only that the satellites re- 

 volve on their proper axis, but also that ^ome parts of their surfaces do very 

 faintly, if at all, reflect the solar rays to us. 



All which has for some time past been observed and noticed by Messrs. Cas- 

 sini and Miraldi, as may be seen in the Memoirs of the Academic Royale, for 

 the years 1707 and J 7 14. 



On the Situation of the ancient Carteia. By John Conduit ^ Esq. F, R, S. 



N° 359, p. 903. 



About 4 English miles N. W. from Gibraltar, at the end of the Bay, there 

 are considerable ruins. The place is at present called Rocadillo, and consists 

 of a few huts, and a modern square tower, which appears to have been raised 

 on the foundation of a much greater pile. The walls of the old city are very 

 easy to be traced. They seem to have been about 2 English miles in circum- 

 ference, and built on the brow of a rising ground. The space within is covered 



3 d2 



