F. W. Very — Nebulosity around Nova Persei. 49 



Akt. Y. — An Inquiry into the Cause of the Nebulosity 

 around Nova Persei / bj Fkank W. Yery. 



The processes by which the nebular illumination around 

 the great nova of 1901 has been produced may conceivably be 

 explained under some one of the following heads : 



First hypothesis : The nebular radiation is emitted from 

 myriads of small gaseous masses, either heated or electrified, 

 which have been evolved in the collision of meteorites, belong- 

 ing to antagonistic and mutually interpenetrating meteor 

 swarms whose motions through space, under the action of 

 gravitation, has brought them together. 



Second' hypothesis : Radiation from the nova, perhaps of 

 Hertzian waves, perhaps of ordinary luminous vibrations^ or 

 possibly of some especially potent ultra-violet rays, but at any 

 rate proceeding in radial lines from the source, has been 

 received upon quiescent matter already existing in the sur- 

 rounding space, and has generated in this matter some chem- 

 ical or physical process attended by radiation affecting a 

 photographic plate, or else the material of space, by simple 

 diffuse reflection, has turned the path of the original rays 

 earthwards without altering their quality. 



Third hypothesis : Powerful explosions from the nova, and 

 the emission of great volumes of excessively hot gases, have 

 been accompanied by violent electric disturbances which have 

 produced extensive discharges of ions under magnetic control, 

 moving with velocities possibly as great as those of electro- 

 magnetic waves, but along magnetic lines of force, instead of 

 radially. The luminous phenomena of the nebula may be 

 conceived either as due to phosphorescence of quiescent mat- 

 ter under impact of the flying ions, or as emanating from the 

 ions themselves. 



Either of these three heads may be subdivided into subordi- 

 nate modes of origin, only a few of which are indicated."^ 

 Since any one of these processes may conceivably produce a 

 luminous effect analogous to the nebula, we must decide 

 between the proposed explanations by considering the objec- 



*Dr. Max Wolf (Astronomisclie Nachriclaten, No. 3752, Bd. 157, 144, Dec, 

 1901) suggests for the origin of the nebula the progression of an explosive 

 wave in detonating gas ('•'Knallgas "), a term which is used to denote an 

 explosive mixture of hydrogen and oxygen, such as is produced in our labo- 

 ratories by the electrolysis of water. Mr. H, B. Dixon, how'ever, has meas- 

 ured the velocity of the propagation of an explosion in a mixture of these 

 gases, obtaining 2819 meters per second, or a quantity which bears no com- 

 parison to the nebular velocity (see Rep. British Assoc, for Adv. Sci., 1885, 

 p. 905). The supposition of an explosion of a mixture of hydrogen and 

 chlorine, which might be started by light from the nova, is open to the 

 same objections as the other radiant hypotheses. 



Am. Jour. Sci. — Fourth Series, Vol. XVI, No. 91. — July, 1903. 

 4 



