272 HUBERT ANSON NEWTON. 



position of the apparent radiant, which gives the direction of the 

 relative motion, and with the knowledge that the heliocentric motion 

 is retrograde, we may easily determine the orbit. 



We have, therefore, five orbits from which to choose. The 

 calculation of the secular motion of the node due to the disturbing 

 action of the planets, would enable us to decide between these orbits. 



Such are the most important conclusions which Professor Newton 

 derived from the study of these remarkable showers, interesting not 

 only from the magnificence of the spectacle occasionally exhibited, 

 but in a much higher degree from the peculiarity in the periodic 

 character of their occurrence, which affords the means of the deter- 

 mination of the orbit of the meteoroids with a precision which would 

 at first sight appear impossible. 



Professor Newton anticipated a notable return of the shower in 

 1866, with some precursors in the years immediately preceding, a 

 prediction which was amply verified. In the meantime he turned 

 his attention to the properties which belong to shooting stars in 

 general, and especially to those average values which relate to large 

 numbers of these bodies not belonging to any particular swarm. 



This kind of investigation Maxwell has called statistical, and has 

 in more than one passage signalized its difficulties. The writer 

 recollects a passage of Maxwell which was pointed out to him by 

 Professor Newton, in which the author says that serious errors have 

 been made in such inquiries by men whose competency in other 

 branches of mathematics was unquestioned. Doubtless Professor 

 Newton was very conscious of the necessity of caution in these 

 inquiries, as is indeed abundantly evident from the manner in which 

 he expressed his conclusions; but the writer is not aware of any 

 passage in which he has afforded an illustration of Maxwell's remark. 



The results of these investigations appeared in an elaborate memoir 

 " On Shooting Stars," which was read to the National Academy in 

 1864, and appeared two years later in the Memoirs of the Academy* 

 An abstract was given in the American Journal of Science in 1865.1 

 The following are some of the subjects treated, with some of the more 

 interesting results : 



The distribution of the apparent paths of shooting stars in azimuth 

 and altitude. 



The vertical distribution of the luminous part of the real paths. 

 The value found for the mean height of the middle point of the 

 luminous path was a trifle less than sixty miles. 



The mean length of apparent paths. 



The mean distance of paths from the observer. 



* Vol. i, 3d memoir. t Series 2, vol. xxxix, p. 193. 



