F. W. Very — Nebulosity around Nova Persei. 51 



mated, in fact the nebular velocities seem to be confounded 

 with those spectroscopicallj observed. I have shown else- 

 where"^ that the gaseous envelopes about the nova, whose 

 existence we inust infer from the spectroscopic observations, 

 belong to an entirely different order of magnitude from the 

 nebulous forms which have been discovered by photography. 

 The latter probably extend to 100,000 solar distances. The 

 general combination of the nebular details into nearly circular 

 rings which have expanded in a continuous manner, requires 

 that the aggregate of the swarms postulated shall be spherical. 



(2) There are various hypotheses assigning the nebular phe- 

 nomenon to the action of radiation from the nova on diffused 

 quiescent matter already existing in surrounding space, for 

 example : {a) The hypothesis of electro-magnetic waves, emit- 

 ted by the nova at its maximum development, exciting lumi- 

 nosity in masses of rarified gas, after the manner of Tesla's 

 disconnected tubes. (^) The hypothesis of dissociation of a 

 compound gas by ultra-violet radiation proceeding from the 

 nova at its maximum intensity, and the subsequent production 

 of light by the recombination of the atoms. {&) The hypothe- 

 sis that luminous radiation from the nova has been reflected by 

 finely divided matter. 



The following objections apply to all three of these hypothe- 

 ses : 1. The duplicity, or possible triplicity of the nebulous 

 ring, and the double ratio of the radii of the two principal 

 rings, are not explained. 2. The expansion of the concentric 

 rings should be uniform, since any supposition of cylindroid or 

 conoidal nebulosities, directed earthwards, is improbable. But 

 instead of uniform expansion in a radial direction, there has 

 been retardation in the movement after a certain time. The 

 deviation from radial direction of movement in special forms 

 does not enter into the argument, which concerns rather the 

 figure produced by the combination of details into an annulus 

 whose outer boundary may be taken to limit the region through 

 which a special process has progressed. 3. The deviation of 

 both rings from the circular to an elliptical shape, and to the 

 same extent, is not easy to explain by radiant hypotheses. Mr. 

 Arthur R. Hinks, of Cambridge Observatory, England, f sug- 

 gests refiection of light from inclined circular rings of nebu- 

 lous material, concentric with the star ; but this requires 

 several years for the completion of each ellipse, whereas the 

 ellipses are already very nearly complete through arcs far in 

 advance of the arrow heads which are supposed to be describ- 

 ing these figures. 4. Finally, the reflection hypothesis in any 



* Astronomische Nachrichten, No. 3771, clviii, 33, Feb., 1902. 

 f Astrophysical Journal, xvi, 198, 1902. 



