Cliangcs 2)rocliiced in Matter hy Electric Waves. 461 



and white varieties of phosphorus. But it is not at all necessary to take 

 only such extreme cases to show the influence of molecular or atomic 

 aggregation in influencing the conductivity. This effect is brought into 

 painful prominence 1)y the variation produced in spite of all precautions 

 in our standards of resistance. 



Experimental Proof of Allot rojnc Changes heinrj attended with Vo/ria- 

 tion of Conducticifi!. — I shall now describe a direct experiment by 

 which the change of conductivity produced in a substance hj molecu- 

 lar change is exhibited. Red mercm^ic iodide is converted into the 

 yellow variety In' the application of heat, and the substance does 

 not return to its original state till after a considerable lapse of 

 time. The recovery here is very slow. A small quantity of 

 mercuric iodide was now placed in a tube provided with sliding elec- 

 trodes, and a current was made to pass through the substance by 

 suitable compression. The conductivity of the substance is rather- 

 small, and therefore a thin stratum should be taken for experiment. 

 The current is ol>s"erved by means of a delicate galvanometer. On 

 the application of heat to the tul)e (which converts the red into the 

 yellow variety), there was at once produced, simultaneously with the 

 molecular transformation, an increase of conductivity. This eff'ect is 

 not due to a rise of temperature, for the increased conductivity was 

 still exhibited on cooling the tube. From this experiment it is seen 

 that the molecular changes can be inferred from changes in the con- 

 ducti\dty. In the case described above, the recovery from the B, or 

 second stage, to the first stage. A, is slow ; but there may be substances 

 (and there are such substances) where, under the given conditions of 

 temperatirre and other physical surroundings, the first stage is far 

 more stable than the second; the substance will then pass back 

 quickly from the B condition to the primitive state, on the cessation of 

 the exciting cause, which gave rise to the transient B effect. The sub- 

 stance will in this case be " self -recovering." 



[Eleetriccd Reversed in the liaxliedion Frodact. 



In the hypotheses given above, it was said that the reaction of the 

 radiation product, or B variety, should be opposite to that of the sub- 

 stance in the normal condition, or in the A state. Thus a negative 

 substance which by the action of radiation shows an increase of 

 resistance during conversion from the A to the B state should exhibit 

 a diminution of resistance when B variety is acted on by electric 

 waves. The contrary would be the case with positive substances. 



The following tabulated statement indicates the phenomena exhi- 

 bited by two classes of substances : — 



