706 PHILOSOPHICAL TRANSACTIONS. [aNNO 1672. 



Ohservationes Jovis ad duos Fixas transeuntis, Derhice Aiiglorum ha- 

 hitce mensibus Febr. et Martii A. 1671-72, st. veteris, a Jon. Flam- 

 steed. N" 82, p. 4036. 



The calculations in this paper, from the old tables of Mr. Street, are of no 

 use now, in the present very accurate state of astronomy. 



Account of the Retuim of a large permanent Spot in the Planet Jupiter, 

 observed by Signor Cassini. N" 82, p. 4039- 



It is now above six years since Cassini published the theory of two sorts of 

 spots, at certain times to be seen in the disk of Jupiter.* 



One sort are nothing but the shadows of the four satellites, which he had 

 often very well observed, when these satellites moving through the lower part of 

 their small circles that environ Jupiter, passed between him and the sun which 

 illuminates him, making a kind of solar eclipse, like that which the moon 

 makes, when she is between the sun and the earth. These spots, as he ob- 

 served from that time, have this peculiar, which distinguishes them from all 

 others, that they are precisely found in that place of Jupiter, where some sa- 

 tellite is seen by the sun ; that they go from the oriental limb to the occidental 

 of the disk of Jupiter, with a motion always equal to that of the satellite; that 

 in respect to us they precede the satellite before the opposition of Jupiter to 

 the sun, and follow him after the opposition ; that the further Jupiter is distant 

 from the opposition, the greater is the apparent distance of the same satellite; 

 that at divers times of the year this distance changes in proportion to the an- 

 nual parallax of the satellite, according as he is differently seen by the sun and 

 by the earth ; and that at one and the same time of the year, when divers satel- 

 lites happen to be between Jupiter and the sun, the spots correspondent to them, 

 are distant from them in proportion to the semidiameters of the circles of the 

 same satellites. 



The other sort of spots have no dependance at all on the satellites; but it 

 geems that they have some resemblance to those spots that sometimes appear in 

 the sun, or to those that are always seen in the moon ; and they are perhaps of 

 the same nature with those that are called belts. These spots also move from 

 the eastern to the western limb of Jupiter's disk ; but their apparent motion is 

 unequal, and swifter near the centre than the circumference, and they never 



* What was discovered of the permanent spot in this planet here in England by M. Hook, An. 

 l66'-t, in May, maybe seen No. 1, p, 3, compared with No. 4, p. 26, No. 8, p, 52, No. 12, p. 68y 

 No, ll. p. 84. 



