648 



PHILOSOPHICAL TRANSACTIONS. 



[anno 1749. 



On the Parabolic Paths of Comets. By Nicholas Struych of Amsterdam, F. R.S. 



From the Latin. N° 492, p. 89. 



That tracing the courses of comets belongs to the principal parts of the sub- 

 limer astronomy, has been established since Newton, 63 years ago, published a 

 problem on finding the paths of comets by 3 observations, on the hypothesis that 

 they describe a parabolic orbit about the sun. By this method. Dr. Halley de- 

 termined, by calculation, the paths of 24 comets, in a table in the Philos. Trans. 

 N° 297. There are indeed 21 different comets. In like manner Mr. S. has 

 noted 18 other comets, not found in that table, in hopes that the periodic times 

 may at length be found. Of these, the path of the comets of 1723 and 1737 

 was determined by Dr. Bradley; that of 1744, by Mr. Betts; of 1 699, 1702 

 1739, by La Caille; the 2d comet of 1743, by Mr. Klinkenberg; the 2d of 

 1746 by M. des Chezeaux ; of the 1st of 1748 by Maraldi. Mr. Struyck gave 

 the observations of the comets seen in 1533, 1678, 17 18, 1729, to Mr. C. 

 Downes to calculate ; but the comets of 1706, 1707, 1742, the first of 1743, 

 and the 2d of 1748, Mr. S. has calculated himself. He also thinks that in May 

 1748, both at Amsterdam and other parts of Europe, on the very same night, 

 3 comets were visible ; of which there is no other certain instance in history. 

 He has also added the comet seen at the end of 168O, and beginning of 168 1 

 because in the last edition of Newton there are emendations, by which is deter- 

 mined the ellipse it described about the sun. He lurther remarks, that of the 

 31 observations he had of the comet seen in 1742, there are 22 whose longi- 

 tudes hardly differ l', and 23 whose latitudes differ not so much as l'. 



The following table shows the paths of the 19 comets above mentioned. 



