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Mr. P. E. Shaw : 



heated to redness in vacuo and left in the same vacuum. 

 Also, if there is this electrolytic action at the contact, we 

 ought to he ahle to get more direct evidence of it than 

 has been furnished so far. 



Bose*, having made an exhaustive investigation of the 

 more common elements, metallic and non-metallic, found : 

 (1) that some elements (e.g. potassium) show an increase 

 and some (<?. g. iron) show a decrease in resistance after 

 receiving electric radiation ; these opposite effects he named 

 negative and positive coherence respectively : (2) that a 

 coherer resistance is liable lo ''fatigue" and "reversal" 

 effects, if the radiation be maintained for long. His theory 

 is that the radiation produces an allotropic modification on 

 the surface of the substance on which it falls. This being a 

 shin effect, and the allotropic modification being unstable, 

 there is a tendency for the contact to return to the normal 

 state. Thus radiation sets up a backward influence against 

 its own action, which increases as time goes on. As less and 

 less effect seems to result from radiation, "fatigue" is seen. 

 The same influences might produce a further effect under 

 certain conditions, so that a positive coherence would give 

 place to a negative one and vice versa: this is " reversal." 

 "Fatigue" and "reversal" are displayed by a very inter- 

 esting series of curve-. 



Now, that molecular changes, with the production of 

 unstable forms, do occur in his experiments, seems indis- 

 putable. For when once coherence has occurred, it is an 

 undoubted fact that metallic conduction occurs throughout 

 the system (the air and oxide films, with their uncertainties, 

 being excluded), so that, there being continuous metal, the 

 "fatigue" and "reversal" must be due to changes in the 

 metal. But whereas Prof. Bose seems to consider that these 

 allotropic changes occur over the whole surface of the bodies 

 used {i.e. wherever radiation can fallf ), surely only the 

 contacts themselves influence the results ! It is in the very 

 restricted area of touch of two surfaces that all changes in 

 resistance occur ; obviously this bridge region must have 

 a preponderating influence in his experiments. 



I have already shown what seems to be evidence of 

 molecular change or " orientation," but to use the term 

 allotropic scarcely seems at present justified. All allotropic 

 change is no doubt molecular, but not conversely ; so that 

 the more general expression seems preferable in the present 

 state of our (want of) knowledge of molecules. 



* Eoy. Soc. Proc. Aug. 1900. 



t This is the only rendering which seems possible from his paper. 



