770 



SCIENCE 



[N. S. Vol. XL. No. 1039 



Morehouse's comet on O&tober 15, 1908. A good 

 series of photographs of the comet was obtained 

 on that date in this country and in Europe, the 

 earliest of these being made at Geneva, Switzer- 

 land. The photographs made at the Terkes Ob- 

 servatory (continuously) on that date with the 

 Bruce telescope extended from e"" 18°" to 13" 28™ 

 C. S. T., or for a period of 7" 10". A set made 

 in France, another in England, and two sets ob- 

 tained by the author with the Bruce telescope of 

 the Terkes Observatory, are available for stereo- 

 scopic combination. It is from the study of these 

 combinations that the following simple explana- 

 tion of the phenomena is derived. 



The photographs all show a twisted appearance 

 of the tail about J° from the head, apparently 

 joined to the head by a slender straight beam. 

 The broken part of the tail became more dis- 

 rupted, and changed more rapidly in the later 

 photographs, until it formed a broad mass with a 

 broad tail. A study of the stereoscopic views 

 shows what really happened. At a time earlier 

 than the first photograph the comet had discarded 

 its tail (by ceasing abruptly to emit matter in 

 that direction) which drifted away into space. 

 For some reason, perhaps from a disturbance due 

 to the cessation of emission at that point in the 

 comet's head, the rear end of the receding tail 

 ' ' buckled ' ' and became twisted into a spiral 

 which finally formed an irregular ring — very much 

 like the smoke ring familiar to the users of to- 

 bacco. Every part of this condensation ring sent 

 out a continuous stream of matter until it formed, 

 roughly, a long open cylindrical tail to the ring, 

 with one end pointed more or less towards us. 



This last phase of the disturbance was the con- 

 dition of the tail at the time of my last photo- 

 graphs of that night. By the next day the rem- 

 nant of the discarded tail had drifted farther 

 away and had become so changed as to be of little 

 interest in connection with its form on October 15. 

 The slender beam of light that apparently con- 

 nected this phenomenon with the head was really 

 a new tail which was forming and which did not 

 touch the masses in the old tail but passed behind 

 them, at a considerable angle as shown by the 

 stereoscope. 



W. W. Campbell: On the Sadial Velocities of 



NehulcB. 



The radial velocities of 54 planetary and ring 

 nebulsB and nebulse of irregular form, have been 

 determined at the Lick Observatory and at the D. 

 O. Mills Observatory in the past three years by 



spectrographic means. The nebulae are remark- 

 able for their high velocities. Only a fifth of the 

 radial velocities are less than 10 km. per second, 

 there are 9 radial velocities greater than 60 km. 

 per second, and the average for the 54 nebulse is 

 42 km. per second. This is 7 times the average 

 radial velocity of the so-called helium stars, which 

 have generally been supposed to be the stars most 

 recently evolved from nebulae. Omitting 12 ex- 

 tended and ring nebute, the average radial velocity 

 of 42 planetary nebulae is 46 km. per second. Two 

 nebulae, close together in the sky, have been ob- 

 served as 202 km. per second recession and 141 

 km. per second approach, respectively, — a relative 

 radial motion of 343 km. per second. 



The prevailing high velocities of planetary 

 nebulas make difficult the continued acceptance of 

 Sir William Herschel's view that the planetary 

 nebulae evolve into stars [whose speeds are of 

 average dimensions]. On the contrary, there is 

 some basis for the suggestion that the planetary 

 nebulae have been formed from the rushing of 

 high-velocity stars through resisting media in 

 space. Eapidly-moving stars are the ones which 

 would have the greatest chance to encounter resist- 

 ing media, and the ooUisional or bombardment 

 effects would be the more effective in generating 

 nebular condition the higher the velocities of 

 impact. 



Hebbr D. Curtis : Preliminary Note on Nebular 



Proper Motions. 



Eoiowledge of the distances and linear dimen- 

 sions of the nebulae are important in studies as to 

 the nature of the nebulae themselves, and especially 

 as to their relation to the stellar system. It is 

 desirable, therefore, that every opportunity be 

 utilized to determine the proper motions of the 

 nebulae. 



Professor Keeler's program of nebular photog- 

 raphy with the Crossley Reflector of the Lick Ob- 

 servatory was inaugurated in 1898, continued by 

 him into 1900, and in the next few years com- 

 pleted by Professor Perrine. A new series of 

 photographs of the same objects, with the same 

 telescope, was begun last winter and should be 

 completed in the early summer of 1915. About 

 one third of the proposed photographs have been 

 obtained to date, and nearly all of these have been 

 compared, as to the accurate positions of nebular 

 nuclei and other very definite masses of nebular 

 Btructure, with the photographs of the same ob- 

 jects secured from twelve to sixteen years ago. If 

 any motions of translation or rotation in the 



