6 INFLUENCE OF A MAGNETIC FIELD UPON THE SPARK SPECTRA OF IRON AND TITANIUM. 



If rings of opposite rotation are forced closer together, their motion will be accelerated, resulting 

 in a shift of the spectrum lines to the violet. Assuming that both directions of rotation are present for 

 electrons producing each spectrum line, the general result will be a widening of all hues as the pressure 

 increases, with a prevailing shift of the maximum of each line toward the red. This last is due to the 

 fact that the condensing action of the pressure on rings rotating in the same direction is assisted by the 

 effort of these rings to get into the strongest part of their mutual field; while for oppositely rotating 

 rings the approach is opposed by the magnetic action, so that on the whole the retardation of the period 

 for a given line is greater than the acceleration, and the line, while being widened toward both red and 

 violet, has its ma.ximum intensity moved toward the red. 



Another theory, by Richardson (43), opposes the connection of pressure displacement with Zeeman 

 effect. Instead of basing his reasoning on magnetic perturbations, Richardson considers the electron 

 as an oscillator which sets up an alternating electrostatic field in its neighborhood. This field would 

 produce forced vibrations in the electrons belonging to neighboring atoms, an effect increased by pres- 

 sure in the medium. The electric field produced by the forced vibrations would then react on that of 

 the radiating electrons. The mathematical development gives a change of wave-length proportional to 

 the pressure and toward the red. Worked out numerically with the available data, the electrostatic 

 resonance theory requires values for the pressure displacement many times greater than those observed 

 experimentally. A modified conception of the equilibrium conditions might account for this discrepancy. 



Richardson objects to Humphreys's theory largely on the ground that the magnetic disturbances 

 of period would be far too small to account for the observed displacements of lines unless the magnetic 

 field for any atom is greater than that corresponding to saturated iron, which Richardson holds to be 

 an upper limit. This is replied to by Humphreys in a later paper (41*, in which he questions the right to 

 base the possible magnetic intensity of iron atoms upon the properties of iron in large masses, since the 

 permeabihty and saturation point depend upon many factors of composition and physical condition. 

 Going farther, Humphreys considers an ideal electron ring and deduces an expression for the change of 

 rotation frequency brought about by an external magnetic field H, such as that due to a neighboring 

 electron ring. This is found to give an expression for the change of wave-length AX in the ether vibra- 

 tions of original wave-length X which reduces to AX/HX- = C, a constant, which is Preston's law for the 

 Zeeman phenomenon, indicating that the ideal electron ring is very similar in structure to the actual 

 radiating particle. If this similarity be admitted, Humphreys is justified in his next step, which is the 

 substitution of known values in the expression for the change of wave-length of ether vibrations pro- 

 duced by a change in the period of the electron ring. This gives a field-intensity for the rotating ring 

 of 45 X 10^, which is about ten thousand times that of the strongest fields used in spectroscopic work. 

 The change in mutual induction by pressing together electron rings having fields of this magnitude may 

 be expected to give sliifts of spectrum lines of the order of those measured. 



A third theory is that presented by Larmor (44), who treats the electron as a Hertzian doublet in a field 

 of electric force. This field would be altered by any change in the distribution of material particles in 

 the medium such as would result from increased pressure. A molecule approaching a vibrating electron 

 would decrease the rigidity of the ether at that point. A lowering of the ether strain would tend to increase 

 the period of the electron, and it is shown that this might give displacements of the magnitude observed 

 for spectrum Unes. A note by Humphreys (4' c) points out that several consequences of Larmor's theory 

 agree only to a hmited degree with observed facts, although his claim that Larmor's equations should 

 give the amount of displacement inversely proportional to the wave-length is incorrect. 



The interacting magnetic atoms of Humphreys seem to provide a very plausible theory, but experi- 

 mental data have been lacking to show the probability of a connection between the effects of pressure 

 and magnetic field on spectrum lines. Humphreys considers that, in general, lines of large Zeeman 

 separation are strongly displaced by pressure, but admits that there is scanty material on which to 



