6S SCIENCE PROGRESS 



the infra-red rays so that they acquire a considerable local 

 kinetic energy. The effect of the local agitation is probably to 

 bring the sulphur atom which stores the electrons emitted 

 from the active metal atom intermittently nearer to the metallic 

 atom, so that the latter " by action at small distances " regains 

 its electrons and so emits its light sooner than it would other- 

 wise have done. The temperature insulation of the centres 

 must be very good, as on cutting off the infra-red radiation its 

 effect continues, just as if the centres remained at their high 

 temperature for some time. If, however, the phosphoroid be 

 first subjected to infra-red radiation and then excited, the pre- 

 liminary irradiation has no effect on the light-emission, which 

 shows that the period of the excited and unexcited centres is 

 different, the latter not resonating to the infra-red rays. This 

 is as might be expected, as the centres are in a different electrical 

 state in the two cases. An interesting fact is recorded by Pauli, 

 who investigated the ultra-violet and infra-red light emitted by 

 phosphoroids — namely, that no phosphoroid which exhibits a 

 marked and prolonged after-glow ever gives infra-red bands ; 

 such bands, if present, presumably accelerate the extinction of 

 the visible bands of the phosphoroid. 



The resonating system is probably the oppositely charged 

 or polarised couplet formed by the sulphur atom and the active 

 metallic atom; and, the extinction spectrum, which gives the 

 efficacy of the different wave-lengths in accelerating the emission 

 of light, will give by its maximum the free period of the polarised 

 couplet. This accords with the theory of dispersion, which 

 shows that the slowest free periods of the molecules correspond 

 not to vibrating electrons, but to whole atoms or groups of 

 atoms in the molecule, which must be electrically charged or 

 polarised as has been imagined. The experimentally found 

 extinguishing spectrum shows that the extinguishing power 

 has a sharp boundary as we go further into the infra-red. 

 Each active metal seems to have the same distribution in this 

 respect, whatever the alkaline metal of the sulphide, although 

 the distribution of excitation of the different bands is different. 

 This accords well with the hypothesis. 



It has been already mentioned that Lenard has shown that 

 the total amount of light energy emitted by a given phosphoroid 

 is the same whether the emission be accelerated by heating so 

 as to last only a few seconds or whether it takes place normally. 



