ARTICLE VIII. 



On the Purturbations of Meteors approaching near the Earth. By Benjamin 

 Pierce, A. A., HoIIis Professor of Mathematics and Natural Philosophy in 

 Harvard University; in a Letter to S. C. Walker, Esq. Read January 15, 

 1841. 



My Dear Sir, 

 Many sources of almost unceasing occupation have prevented my giving Mr. 

 Erman's* paper on Meteors that early attention which I intended. I shall now 

 turn my attention to the point which you suggested of the earth's attraction. Al- 

 most the whole labour has fortunately been saved for me by Laplace, in the Mec. 

 Cel., Vol. IV., Book IX., Chap. II., " On the Perturbations of a Comet, when 

 it approaches very near to a Planet." He has there proved (8038, Bowd. Ed.,) 

 that " we may, in the calculation of such a comet, suppose the planet to have 

 a sphere of activity, in which the relative motion of the comet is affected only 

 by the planet's attraction ; and that beyond this point the absolute motion of the 

 comet about the sun is performed in exactly the same manner as if the sun 

 alone acted upon it." The radius of this sphere is by (8035) 



r.\l{\m')\ 

 in which 



r = the radius vector of the planet, 

 m — its mass divided by the sun's mass; 

 so that, in the present case, this radius, which we denote by ^o , is 



r^ = 0-0053, 

 in which the unit is the same as Erman's. 



Now the relative orbit of the meteoric ring is directed nearly to the centre 



* Schumacher's Astr. Nachr., No. 385. 



