268 Prof. Bessel's Additions to the Theory of Eclipses, 



FAM. B. Species. Icon. 



6.Ennych. Luctualis, Hubn. Hubn. Pyral. tab. 14. f. 88. (mas. 



7. — Octomaculalis, Treit.*...Hubn. Pyral. tab. 12. f.75. (fcem. 



8. — Pollinalis, Hubn Hlibn. Pyral. tab. 5. f. 29- (mas. 



9- — Quadripunctalis, Fabr..Hiibn. Pyral. tab. 12. f. 76. (foem. 



10. — Nigralis, Fabr Hubn. Pyral. tab. 5. f. 26. (mas. 



11. — Atralis, Hubrvf Hubn. Pyral. tab. 5. f.27. (mas.) 



End of Volume 7. 



[To be continued, as soon as the next volume shall have been received.] 



* En nyc hi a, Stephens. 



•f- Nee Py. atralis, Haw. et Curtis; istaec enim species Enn. octomaculali 

 Treitsch. (Guttali, scilicet H'ubneri) convenit. 



XLI V. Additions to the Theory of Eclipses, and the Methods of 

 calcidating their Results*. 



[1.] "C^OR calculating the results of eclipses two methods, 

 ■*■ founded on different principles, have been hitherto 

 employed. The first follows up the phenomenon in the man- 

 ner in which it presents itself to the observer. It requires, 

 therefore, the calculation of the apparent distances of both 

 the eclipsing and the eclipsed bodies from the pole, as also of 

 their apparent semidiameters, in order to find, by means of 

 the former together with the distance of the centres resulting 

 from the apparent diameters, the angle at the pole; it requires 

 besides the calculation of the change of this angle produced 

 by parallax, in order to deduce, by applying it to the angle at 

 the pole, the corresponding angle which would be observed 

 in the centre of the earth ; this method finally gives from the 

 magnitude of this angle and the rate of its change as deduced 

 from the tables of both objects, the time elapsing between the 

 moment of the observation and that of the conjunction of 

 both bodies, by which the latter expressed in time of the place 

 of observation is derived. This method is very old ; Kepler 

 has already explained it ; in modern times it has been deve- 

 loped by Lalandef, and more completely and accurately by 

 Bohnenberger \. Both adopt for the pole that of the eclip- 

 tic ; Gerstner §, however, refers all the calculations which the 

 method requires to the pole of the equator. Carlini || has 

 lastly improved this method by calculating the parallax, in the 



• From Schumacher's Astron. Nachrichten, No. 151. 

 -j- Astronomie, § J977- 



% Geogr. Ortsbestimmwig (Determination of the geographical Position 

 of Places), p. 323. § Ash: Jahrb. 1/98, p. 128. 



|| Zach's Corresp. vol. xviii. p. 528. 



case 



