148 Astronomical and Nautical Collections. 



in —2' 57", in latitude +30"; quantities not at all considerable 

 for the first rough estimate. 



§ 52. 



We have many tables for finding the true anomaly of a comet 

 from the time given, and the time from the anomaly, which are 

 to be found in astronomical works and collections. But the 

 most convenient and complete is unquestionably that which is 

 contained in a book not very bulky and but little known, 

 though extremely valuable, entitled, An Account of the Dis- 

 coveries concerning Comets, by Thomas Barker, Gent. 4. Lond. 

 1757. Pp. 54, 1 plate. The second table in this little work 

 gives, for every five minutes of the true anomaly, the cor- 

 responding parabolic area, and the logarithm of the distance, 

 with the first differences, supposing the distance at the perihelium 

 unity ; and hence the true anomaly and distance from the sun 

 may be found for every comet, and for every given time, with 

 perfect accuracy, by a calculation which is much simpler than 

 that which is required by the common tables. It is much to be 

 regretted that Barker's essay was not known to Pingre'. The 

 mode of finding- the orbit, described in it, is that of Newton, 

 adapted to calculation by the author, and illustrated by a 

 particular specification of all the triangles and proportions re- 

 quired in it. We find three valuable observations of the great 

 and celebrated comet of 1744, almost six weeks earlier than 

 those which are more commonly known, communicated to 

 Barker by Morris ; they are 



The hour was not recorded, but Barker supposes that it 

 may have been about 8 or 9 in the evening, or 8h. 17m. ; and 

 he finds that these observations agree with the parabolic 

 elements of the comet. [The table is also reprinted in Sir 

 Henry EngleJieldCs Essay On the Determination of the Orbits of 

 Comets, according to the Methods of Father Boscovich and M. 

 de Laplace, 4. Lond. 1793. Pp. 204, 4 plates; but without 

 corrections : it is here presented in an improved form, having 



