1869.] 



219 



[Kirkwood. 



November group is somewhat greater than that of the comet of 1866, are 

 in striking harmony with the views here presented. 



5. Owing to tliis loss of matter, periodic comets must become less 

 brilliant, other things being equal, at each successive return ; — a fact 

 observed in regard to the comets of Halley and Biela. 



6. The line of apsides of a large proportion of comets will be approxi- 

 mately coincident with the solar orbit. The point towards which the sun 

 is moving is in longitude about 260'^. Tlie quadrants bisected bj'' this 

 'point and that directly opposite extend from 215° to 305°, and from 35° 

 to 125°. The number of cometary perihelia found in these quadrants up 

 to July, 1868, (periodic comets being counted but once) was 159, or 62 per 

 cent. ; in the other two quadrants, 98, or 38 per cent. 



This tendency of the perilielia to crowd together in two opposite 

 regions has been noticed by different writers. 



7. Comets wliose positions before entering our system were very remote 

 from the solar orbit must have ocertalien the sun in its progressive mo- 

 tion; hence their perihelia must fall for the most part, in the vicinity of 

 the point towards which the sun is moving; and they must in general 

 have very small perihelion distances. Now, what are the observed facts 

 in regard to the longitudes of the perihelia of the comets which have ap- 

 proached within the least distance of the sun's surface? But three have 

 had a perihelion distance less than 0.01. All these, it will be seen by the 

 following table, have their perihelia in close proximity to the point re- 

 ferred to: 



I. Comets whose Perihelion Distances are Less than 0.01. 



In table II. all but the last have their perihelia in the same quadrant. 

 II. Comets whose Perihelion Distances are Greater than 0.01 and Less 



than 0.05. 



The perihelion of the first comet in table III. is remote from the 

 direction of the sun's motion; that of the second is distant but 14°, and 

 of the third, 21°. 



