378 PHILOSOI'HICAL TRANSACTIONS. [aNNO 1 676-7, 



the other part; so that this planet, by a rotation about its axis, or by an exposi- 

 tion of the same hemisphere to Saturn, much after the manner of the hemi- 

 sphere of the moon to the earth, sometimes turns to us the part analogous to 

 the continent, sometimes that part which answers to the sea. 



This vicissitude of phases in this planet was the cause that it could not be 

 found since it was first discovered in the year 1671, till the middle of Dec. 

 1672; after which time it disappeared once again, until the beginning of Feb. 

 1673, at which time, having been observed 13 days successively, it afforded the 

 opportunity of determining the period of its motion. 



Since that time, as often as Saturn has been distant enough from the sun to 

 enable us to discern this planet, it has always been seen in all its occidental di- 

 gressions and in the conjunctions with Saturn, which have since happened with 

 a great latitude, as well in the upper part of its circle as in the lower, and it 

 could never be seen in the oriental digressions, where it remains invisible in 

 every revolution of 80 days for a whole month together. 



It begins then to appear 2 or 3 days before the conjunction in the inferior 

 part, and to disappear 2 or 3 days after the conjunction in the superior part. 



The other planet, which was discovered about the end of the year 1672, has 

 its greatest digression from the centre of Saturn only one diameter and two- 

 thirds of his ring, and the period of its revolution about Saturn is 4 days and a 

 half, but more precisely, 4 days, 12 hours, and 27 minutes. Its latitude aug- 

 ments also according as the ring enlarges. We have not yet been able to dis- 

 tinguish it in the conjunctions, either in the upper or lower part of its circle, 

 but only in the greatest, as well oriental as occidental, digressions. And this 

 satellite being alternately one day towards its conjunction and the other day to- 

 wards the digression, it is ordinarily seen only every third day, and rarely 2 

 days together, when it falls out that at the hour of observation it is in the 

 middle between the conjunction and digression. 



Lastly, the apparent magnitude of these planets is so little, that posterity 

 will have cause to wonder that their discovery was begun by a glass of 17 feet. 



An Account of some Books. N° 133, p. 833. 



I. Pharmacopoeia Collegii Regalis Lond. A. 1677^ in fol. 



II. Catalogus Plantarum Angliae, et Insularum adjacentium, tum indigenas, 

 tum in agris passim cultas complectens, &c. edit, secunda; operd Johannis 

 Raii, M.A. e Soc. Regia. Lond. 1 677, in 8vo. 



In this edition the accurate and learned author presents the curious with a 

 considerable number of plants not contained in the first, which amount to about 



