460 



SCIENCE. 



[N. S. Vol. VIII. No. 197. 



but north of the solar equator the lotational 

 force is in one direction, and south of it in 

 the other. 



It is genei'ally impossible to indicate a 

 point in the tail of the comet ; the exception 

 occurs on the plates of April 5, 6, 7, 8 and 

 10, where a bright detailed structure is re- 

 ceding with increasing velocity of from one 

 million to twenty-five million kilometers 

 per day. The velocity of recession is 36 

 times the acceleration of gravity, and does 

 not agree with any of the velocities re- 

 quired by Bredichin's hypothesis. The 

 spectrum, as given by an objective prism^ 

 of the head and tail showed five bands 

 probably due to hydrocarbons. A further 

 test of the theory of axial rotation of 

 comets near the sun would be an ob- 

 served change of direction or speed of rota- 

 tion in the solar magnetic field. Another 

 would be the observation of the rotation 

 when the tail is directed approximately to- 

 ward the observer. 



Professor Edward C. Pickering presented 

 to the Conference a letter he had received 

 from Professor H. H. Turner, of the Uni- 

 versity Observatory, Oxford, England, con- 

 veying a provisional statement in reference 

 to measures and comparisons made of plates 

 forwarded him by Professor Pickering. He 

 writes in part : " The optical distortion on 

 the plate is quite small, if existent — up to 

 3° from the center, and perhaps further. 

 "Whatever may be the ultimate definitive 

 result as regards optical distortion, your 

 plates will give (by the allowance for such 

 distortion, which will be quite easy) as good 

 places as we are getting on the plates for 

 the Astrographic Catalogue. The images are 

 perhaps a little larger and more diffused, 

 but are quite easy to measure. This holds 

 for certainly 4°x4°, and probably further. 

 If I am right in believing that fear of optical 

 distortion was the motive for rejecting the 

 photographic doublet the above conclu- 

 sions show this fear to have been ground- 



less, and the manifest advantages of get- 

 ting a large field at once prove the doublet 

 to be the right instrument, certainly for 

 charting purposes. If you think this brief 

 note will be of any interest at the Confer- 

 ence, please make use of it." 



The subject of ' The November Meteors' 

 was discussed, and Professor Pickering re- 

 ferred to the desirability of obtaining ob- 

 servations in various parts of the sky and 

 in various longitudes, as indicated in a cir- 

 cular issued by the Harvard College Obser- 

 vatory. Professor Barnard recommended 

 the short-focus lantern lens in the photog- 

 raphy of the meteors. Professor Pickering 

 referred to the fact that at present there 

 seemed to be no available method of de- 

 termining the direction of motion of the 

 meteor fi-om its trail on the plate. Profes- 

 sor W. H. Pickering suggested the desira- 

 bility of pointing the camera in the neigh- 

 borhood of the radiant. Third-magnitude 

 meteors could thus be photographed. Pro- 

 fessor Barnard indicated that meteors 

 seemed to become visible some distance 

 from the radiant. Professor Hale referred 

 to Doctor Elkin's experience as indicating 

 the photographic diificulties. Professor 

 Searle stated that since small meteors ap- 

 peared near the radiant, and large ones 

 away from the radiant, it was probable that 

 the body of the meteor concealed the light 

 when near the radiant. Professor Eastman 

 said the experience of most observers is 

 that the largest meteors appear at some dis- 

 tance from the radiant. It seems quite 

 likely that Professor Searle's hypothesis 

 gives the true explanation. Professor Bar- 

 nard thought that, since meteors must pene- 

 trate some distance before attaining high 

 illumination, perspective would show them 

 at some distance from the radiant. Profes- 

 sor Eastman suggested the photographing 

 of persisting meteor trails. Professor Bar- 

 nard had seen the smoke for ten minutes, 

 and in one case thirty minutes, after the 



