254 Profs. D. N. Mallik and A. B. Das 



on 



strained condition imposed by the nature o£ the gas. Hence 

 the spectrum must be complex under these circumstances. 



At a very low pressure, however, on account of the simpler 

 conditions that prevail, the modes of motion must be fewer, 

 and the corresponding spectrum also simpler in consequence. 



2. Under these circumstances also an application of a mag- 

 netic field is more likely to result in an effect being produced 

 than under ordinary conditions. Moreover, if a vortical 

 spin is associated with the structure of an atom and each 

 period of a spin corresponds to a line in the spectrum, a 

 change in the spin, conceivably produced by an impressed 

 magnetic field, and a corresponding change in period must 

 lead to a displacement of the lines. 



It will follow also that the gas ought to show a simplified 

 spectrum, which may be the same for all gases. 



Experiments, so far as they have gone, tend to confirm 

 ■these conclusions. 



3. When photographs of spectra of air are taken at different 

 pressures, it is found (PI. IV. fig. I., spectra of air for pres- 

 sures between 33 to 3 mm.) that there is no change up to a 

 pressure of -ywo °^ millimetre in a tube of length 14*5 cm. 

 with an induction-coil giving a spark-length of 29 mm. in 

 atmospheric air. 



4. At a pressure of about ^ millimetre, however, the 

 character oi the spectrum seems suddenly to change, giving 

 a partially simplified spectrum (PI. IV. fig. n., spectra 2, 4), 

 while a simple spectrum of four lines, consisting of four of 

 the original lines, is obtained when the pressure is about 

 I^q-o of. a millimetre (PI. IV. fig. v., spectrum 3). Figs. in. 

 and IV. represent intermediate stages. 



On introducing the magnetic field there seems to be a 

 small shirt, which, however, requires further examination 

 (PI. IV. fig. v., spectra 1, with the magnetic field on, 2, with 

 the field reserved, 3, without the field). 



5. If this shift is not fortuitous, it ought to prove of great 

 theoretic interest. Larmor has shown that on his (or any 

 other) dynamical theory of the electromagnetic field, an 

 effect ought to be observable in a strong magnetic field, 

 which, however, Lodge failed to detect. 



It may be observed that if any such effect is to be observed it 

 is more likely to be detected under the simpler conditions that 

 obtain in high vacua than in those in Lodge's experiments. 



6. It will be noticed that at a certain low pressure the 

 magnetic field produces increased illumination (PI. IV. 



;figs. IV., v.). When a simplification of spectrum occurs at a 



