60 J\f)\ Jawe>i Rice on 



anticathodes of the heavy metals, such as platinum, palladium, 

 rhodium, tungsten can l)e made to emit radiations with wave- 

 lengths equal to about half of an Angsti'om unit, or -05 millimicron. 

 Lighter metals radiate with wave-lengths somewhat longer, for 

 example about -15 millimicron for copper. 



Before leaving this explanatory jjortion of my lecture, I ought 

 to mention that we cannot escape the conclusion that those oscil- 

 lations which we can excite in material bodies by hammering, 

 bending, etc., and which give rise to aerial vibrations producing 

 the sensation of sound, also give rise to ethereal vibrations, 

 which, however, would be in the main of excessive wave-length 

 and of the feeblest intensity. Also all that oscillatory motion 

 in the molecules which we call the heat-motion must give rise to 

 ethereal vibrations, even when the body is not luminous ; in fact 

 such vibrations do constitute some part of the infra-red vibrations. 

 The shortest qualities of the infra-red, however, together with the 

 luminous ultra-violet waves originate from mechanisms within the 

 atom, no doubt the rings of electrons, constituting the " planets " 

 of the " solar system " to which now-a-days we liken the structure 

 of the atom. In X-rays we are doubtless receiving intimations 

 of violent changes going on in the very interior of the atom itself, 

 its innermost rings of electrons, perhaps even in its very nucleus, 

 that positively electrified core which seems to hold the negative 

 electrons in their orbits against centrifugal action and mutual 

 repulsion. 



What picture does all this give us of the condition of the 

 ether with which we have had perforce to fill our universe. One 

 whose very complexity it seems hopeless to analyse, compared to 

 which the most violently agitated water surface seems simplicity 

 itself. Yet that hopelessness is not justified. In the grating and 

 radiometer we have means of analysis which have brought us 

 considerable knowledge, and the past history of science fully 

 supports the view that out of all the seeming disorder the mind 

 of man will evolve order. Indeed he has already made a good 

 start, but one serious difficulty confronts him. 



