494 



SCIENCE 



[N. S. Vol,. XXX. No. 771 



spectroscopic measures of Comet Morehouse at 

 the Yerkes and Lick Observatories show that 

 the light from the tail proceeds almost entirely 

 from gaseous molecules. But Schwarzschild 

 has shown that there can be very little light- 

 pressure on free gaseous molecules, because 

 their dimensions are so small that they dif- 

 fract the light and remain themselves com- 

 paratively unaffected. If the motion is due to 

 pressure of light, it would seem to follow that 

 the gaseous spectrum of the comet's tail must 

 be that of small separate atmospheres envel- 

 oping and attending moving particles which 

 are not otherwise visible, but are the objects 

 directly impelled by the luminous impact. A 

 gradual diminution of size of the particles by 

 electric dissipation or by evaporation would 

 give a diminishing efficacy to the repulsion, 

 but whether this would be compatible with the 

 observed motion can not be determined. 



The cometary evidence being indecisive, the 

 argument for the interaction of ether and 

 matter must rest for the present on the ob- 

 served mechanical pressure of light, and on 

 Kaufmann's experiment, with the addition of 

 such inferences as are suggested by the phe- 

 nomena of radioactivity and the behavior of 

 matter in highly exhausted vacuum-tubes. 



The variety of new properties of matter ob- 

 served with a high vacuum is sufficiently ex- 

 traordinary. The interior of a vacuum tube 

 is virtually a new world, where the physical 

 laws with which we are familiar are in appear- 

 ance frequently contravened. According to 

 the ordinary laws of gases, any gas set free in 

 a vacuum-chamber might be expected to dif- 

 fuse almost instantly to every part of the 

 exhausted volume. Nevertheless, in heating 

 the gas-regulator of an X-ray tube to restore a 

 minute amount of gas to a tube of too high 

 resistance, the gaseous matter may be seen 

 trielding along the walls of the tube in a net- 

 work of apparently viscous filaments, the gas 

 behaving as if it were a viscid liquid, ad- 

 hering to the walls of the tube and reluctant 

 to leave them. 



In my paper " An Inquiry into the Cause of 

 the Nebulosity around Nova Persei " ^ I have 



'American Journal of Science, July, 1903. 



shown that particles analogous to those of 

 cathode rays were shot off from the star with 

 velocities in some cases scarcely inferior to 

 that of light; and yet, at distances from the 

 center of dispersal which are comparable with 

 those from star to star, the motion bore wit- 

 ness to a control which was not gravitational, 

 but resembled rather a magnetic control ema- 

 nating from the star. The mere suggestion 

 that a magnetic field can exist at stellar dis- 

 tances capable of guiding particles, of any 

 kind whatsoever, will evoke the exclamation 

 " impossible ! " But having learned from the 

 behavior of vacuum-tubes that many very 

 strange phenomena are of every-day occur- 

 rence in these novel realms of vacuous space, 

 it may be well to enlarge the bounds of pre- 

 conceptions. 



Professor Speyers's equation (7) does not fit 

 the facts, but his equation (8), which agrees 

 with that given by Professor Lewis, conforms 

 to the data of observation. The source of the 

 discrepancy comes from a failure to distin- 

 guish between the mass of the ether and that 

 of the body receiving radiation. If, for clear- 

 ness, we call the former m' and the latter m. 



and 



dE = Y'-m' = V-d 



: mv = M 



(if the velocity of the body receiving the radia- 

 tion is wholly due to light-pressure, M being 

 the temporary momentum of the ether), 

 whence, since m<=m^-\- dm, 



dm/n% ^v/ (V — v) . 



This equation may be substituted for equa- 

 tion (Y)." It gives for the mass of a particle 

 moving at any velocity up to that of light, 



, dm , V 



or 



mi — m„ ==•!;/( F — v) 



if ■!; ^ F, as the theory of Kaufmann's experi- 



ment requires. 



: that " the mass of the body struck 



In saying ■ 

 ^ Loe. cit. 



