126 THE FIELD OF EXPERIMENTAL RESEARCH. 



source of the Becquerel rays is another niysteiy apparently far from 

 being cleared up. and if it be true, as recently announced, that a sub- 

 stance named radium has in reality 900 times the power of emitting 

 these rays than is possessed by uranium and thorimu, and that the 

 radiation is able to cause visible liuorescence of Ijarium platinoc3'anide, 

 the mystery but deepens and makes us again think of the possible exist- 

 ence of obscure ra^^s only absorbed and converted by a few special 

 substances. 



The diffusion which takes place when Kontgen raj^s pass through 

 various media is another })li(Miomenon which needs more attention from 

 investigators. This effect seems to be produced by all substances in a 

 greater or less degree. It, however, appears to be nearly absent in 

 the case of those substances which give out light or fluoresce luider the 

 rays, as barium platinocyanide and calciuui tungstate. It will be 

 important to determine definitely whether the rays diffused by different 

 substances are lowered in pitch or penetrating power as compared with 

 the rays exciting the diffusion ; whether, in other words, the rays from 

 a tube with quite high vacuum excite similar rays by diffusion, or rays 

 more absorbable, and if a lowering takes place whether it occurs in 

 like manner and degree for all diffusing media. 



The phenomenon may be akin to fluorescence, as when quinia sul- 

 phate converts the invisible ultraviolet rays of the spectrum into lower 

 rays or visible light. This action may be at its extreme when barium 

 platinocyanide, excited b}' Rontgen rays, so lowers the pitch as to pro- 

 duce rays within the visible spectrum, for this compound gives very 

 little or no Rontgen-ray diffusion. Are there substances which under 

 Rontgen rays fluoresce with invisible rays of the order of the ultra- 

 violet of the spectrum? If, as is the case with solid paraflin, the irra- 

 diated substance gives rise to considerable diffusion, it can, as I have 

 noted, produce a secondary diffusion in other masses of the same sub- 

 stance, or of other substances, as indicated by feeble fluorescence of 

 the sensitive barium salt, thoroughly screened from the direct source 

 of rays and from the first or primary diffusion. It is probable that 

 Tertiary diffusion could be found if we possessed a far more powerful 

 or continuous source of the rays for exciting the initial diffusion. The 

 ra}^ emission, even in the most powerfully excited tube, is probably so 

 intermittent that the active period is but a fraction of the total time. 

 It maj^ easily be that the limit of intensity of Rontgen-ray emission 

 has not yet been reached, especially when artificially cooled anticath- 

 ode plates are available. 



There is much room for experimental work in this fascinating field. 

 We need for it the means for the production either of a continuous 

 electric discharge at from 60,000 to 100,000 volts or a high-frequency 

 apparatus capable of giving an unbroken wave train; that is, a succes- 

 sion of high period waves of current without breaks or intermissions. 



