64 Mechanical Philosophy, 



ality and the time of its diurnal motion. He has 

 published new and valuable observatians on the 

 sun, the moon, and indeed on almost all the bo- 

 dies belonging to the solar system. He has greatly 

 enlarged our acquaintance with the fixed stars; 

 and, in a word, so much extended our knowledge 

 of astronomy, that his life may be considered as 

 forming one of the most important aeras in the his» 

 tory of this branch of philosophy. 



At the close of the seventeenth century, the 

 respective diskmces of the several planets from the 

 sun were far from being accurately determined. 

 These, by successive observations, have been since 

 ascertained, with a great degree of precision; and 

 the various astronomical uses which this knowledge 

 is calculated to subserve, have been displayed in 

 the most satisfactory manner. Particularly the 

 observations made by many philosophers on the 

 transits of Venus and Mercury, which the eigh- 

 teenth century exhibited, have thrown much light 

 on this subject, and on several questions of great 

 importance in astronomy. 



It is but a few years since our knowledge of 

 Comets was in its infancy. Dr. Halley, at the 

 beginning of the period under consideration, made 

 the first attempt to give a systematic view of this 

 part of the science in his Synopsis Astronomice 

 CometiccC, published in 1705, But his inquiries, 

 concerning these excentric bodies, though inge- 

 nious and highly valuable, were far from being 

 adequate or satisfactory. By the labours of mo- 

 dern astronomers, our acquaintance with the 

 comets has been wonderfully extended. Sixty 

 eight new ones have been observed ; the return of 

 many of them has been ascertained and demon- 

 strated,"" and many curious facts respecting them 



a M. De LA Lande, in his History of Astronomy, for the year iSoiy 



»Etim»tes, that the observations which took place in the course of that year 



