420b annals new YORK ACADEMY OF SCIENCES 



above explained, or more likely because no special effort has been made 

 to reproduce them experimentally under suitable conditions, I anticipate 

 that they will eventually prove to be of similar origin. 



If the comet's train be a beam of radiant matter, the following phe- 

 nomena might attend upon the earth's transit through it: (1.) Being 

 composed of negatively charged electrons (the smallest conceivable par- 

 ticles of matter), each with a long, free path or collectively at compara- 

 tively great distances apart, it must consist of highly attenuated material 

 such as Faraday and Crookes regarded as a fourth state of matter. (2.) 

 It could exist only in a near vacuum and, therefore, impinging against 

 our atmosphere, it could only penetrate its superficial and highly rarefied 

 exterior. There it might develop a slight phosphorescence, but as this 

 would occur on the lighted side of our planet, it would be invisible to us. 

 The beam would thereby however become arrested or would terminate. 

 (3.) During the earth's immersion in the comet's train, those of us near 

 the center of its night or dark side would see it passing on all sides as a 

 faintly luminous cylinder, extending above us into space, but modified 

 perhaps by perspective to an apparently coronal form like an aurora. 

 To those of us near the terrestrial horizon beyond the area locally illumi- 

 nated by sunrise or sunset, it might appear brighter than to those nearer 

 the night center. (4.) The behavior of the comet's train would, how- 

 ever, perhaps depend upon its direction with respect to the magnetic axis 

 or polarity of the earth. In certain directions, it would possibly or even 

 probably be repelled by the earth's magnetism wholly to one side so that 

 we should escape it altogether. (5.) Whether deflected or not, it might 

 occasion terrestrial magnetic perturbations as does the aurora. (6.) If 

 not deflected by the pressure of its impact, it might disturb the equi- 

 lil^rium of the atmosphere and so commingle the upper and lower air as 

 to produce a reduced temperature. 



Whether there is in this hypothesis anything inconsistent with the 

 assumption that comets' trains may consist of any kind of matter indi- 

 cated apparently by spectroscopic records, or of associated meteoric par- 

 ticles projected simultaneously by the pressure of light, has yet to be 

 demonstrated, if possible. Their development in unlimited vacuous 

 space seems to involve a condition beyond experimental provision. It is 

 of interest in this connection that certain kinds of solid matter slow 

 with a vivid phosphorescence under the cathode rays and give a line 

 spectrum very similar to that of the substance indicated when in the 

 condition of an incandescent gas or vapor. 



According to this hypothesis, little effect need apparently be antici- 

 pated upon the earth from Halley's comet, in case its train is traversed 

 well away from its head. 



