Page:Collected Physical Papers.djvu/210

190 observed by Minchin, that the immediate result is a transitory negative followed by the normal action. A reversed response is also observed under molecular modification.

If the action of light is prolonged beyond the attainment of maximum effect, a tendency appears towards, or actual reversal.

In fig. 41 is given an interesting series of results showing the growth of fatigue, the different phases culminating in an actual reversal (compare with fig. 37). It will be seen that in the second, response was feebler,

and a tendency towards reversal had already taken place after an exposure of about 9 seconds. In the third, the response is feebler still. In the fourth, the normal response lasting for 3 seconds, is extremely weak; there is then a reversal of response which is fairly strong. On the stoppage of light the reversed effect persists for some time. After the fourth, the responses become reversed.

It will thus be seen that both electric radiation and light produce similar conductivity and electromotive