328 



SCIENCE. 



[N.S. Vol. XVII. No. 426. 



those of the ninth and tenth magnitudes; 

 (2) that the average linear velocity with 

 which these faint stars move through space 

 is of the same order of magnitude as that 

 of the brighter stars and about fifty per 

 cent, greater than the velocity of the sun. 



An Inquiry into the Cause of the Nebulos- 

 ity around Nova Persei: Prank W. 

 Very. 



Lockyer's hypothesis of colliding meteor 

 swarms would require spherical swarms of 

 enormous dimensions, and in other re- 

 spects it does not fit the facts. Radiation 

 hypotheses do not explain the duplicity, or 

 possible triplicity, of the nebulous ring, 

 nor the double ratio of the radii of the two 

 principal rings; neither is the retardation 

 of the expansion satisfactorily accounted 

 for. Eeflection hypotheses are absolutely 

 barred, because they demand an impossible 

 albedo in the nebula. 



The supposition that the motion is a real 

 one involves the further hypotheses that it 

 is due to particles of corpuscular dimen- 

 sions, expelled from great masses of in- 

 tensely heated gas, surrounding the nova, 

 in moments of powerful electric oscillatory 

 discharges; that these discharges assist to 

 ionize the material and start a series of 

 instantaneous magneto-electric impulses 

 which guide the moving particles along 

 lines of magnetic force; that the material 

 is probably diamagnetie and will finally 

 come to rest in loci of least magnetic 

 potential; that the velocity imparted 

 depends on the masses of the ions which 

 appear to be in the ratio 1:2:4; that 

 the velocity is accelerated out to a radius 

 at which magnetic repulsion and gravita- 

 tional attraction are equal for particles of 

 the given dimensions, and that at greater 

 distances the velocity is retarded. An 

 estimate of the mass and diameter of the 

 nova indicates that, at the surface of the 

 star, the ratio of magnetic force to gravity 



may be as great as 100,000 to 1 for these 

 minute particles ; and as such a force would 

 be capable of generating in a corpuscle a 

 velocity of 100,000 km. per sec. in one sec- 

 ond, if it were possible fully to utilize it 

 for this purpose, the only objection which 

 can be urged against the hypothesis is the 

 diificulty of imagining a process by which 

 this force can be economically applied. 



In favor of the hypothesis it can be 

 stated that the theoretical variation in the 

 rate of expansion of the nebula has been 

 observed; that the observed motions of 

 nebulous forms agree well with those to be 

 expected if the phenomenon is a species of 

 magnetic phantom; that there are curved 

 and diverging streamers on the south-south- 

 west side, resembling the sheaves of diverg- 

 ing coronal filaments about the sun 's poles ; 

 that the absence of a corresponding sheaf 

 on the north-northeast side may be ex- 

 plained on Doppler's principle; that the 

 disappearances of certain forms in the 

 outer of the two principal rings after 

 reaching a radius of 14' to 16', and the 

 phenomenal and sudden appearance of 

 bright forms at about the same positions, 

 are to be explained on the same principle ; 

 that such appearances and disappearances 

 are demanded on the magnetic hypothesis, 

 and are extraordinary anomalies on any 

 other. 



It is concluded, therefore, that the neb- 

 ula resembles a gigantic corona; that its 

 axis is inclined 40° to the line of sight on 

 the south-southwest side; and that the ex- 

 pansion of the nebula is approaching its 

 limit. 



The Mounting of Fixed Meridian Instru- 

 ments: G. W. Hough. 

 The variation in level and azimuth in 

 fixed meridian instruments is due to the 

 effect of temperature: (1) On the metal 

 outside the piers, (2) on the metal in the 

 piers, (3) ©n the supporting piers, and (4) 



