igii.] 



IN THE TAIL OF HALLEVS COMET. 



259 



Of comet ?iIorehouse this observatory possesses about sixty nega- 

 tives taken by Mr. E. C. Slipher. Among them are many pairs, the 

 one plate following the other on the same evening. From the assort- 

 ment thus offered I have selected two sets for measurement, the one 

 a pair taken on October 31, 1908, at 8h om zb to 8h 42m ± M.S.T. a-;d 

 from 9h 14m ±: to I oh 8m ± respectively ; and the other a triplet on 

 November 16. 1908, No. i being taken at 6h 25m to yh 13m; No. 2 

 at yh 24m to yh 50m ; No. 3 at 8h om to 8h 32m, respectively. I 

 chose four knots on one and five on the other with the following 

 results : 



Tail of Comet Morehouse, October 31. 



6. It will at once be seen that both sets of plates show accelerated 

 velocity in the particles of the tail away from the head as the dis- 

 tance from the head increases. In the first set the acceleration is 

 fairlv uniform, while in the latter the velocity does not increase until 

 the distance out has become considerable. This afifords the reason 

 whv some observers have failed to detect the motion. It is at times 

 and in certain places masked. For this the following explanation 

 mav be oflr'ered : In the neighborhood of the head the several emis- 

 sions are violently contorted as a mere inspection of the photographs 

 show, and in consequence must be subject to collision with other por- 

 tions of the tail. Possibly they encountered here matter in space 

 which speaks unspeakably of motion other than that due solely to 

 repulsive force. If now an observer chanced to make his measures 



rROC. AMER. PHIL. SOC. L. I99 Q, PRINTED JUNE 29, 19II. 



