GEO-ELECTRIC RESPONSE 443 



already demonstrated by the alternate cooling of the upper 

 and lower surfaces is again seen here : namely, that it is the 

 upper surface which exhibits the true excitatory effect, by 

 induced concavity in the case of mechanical and by galvano- 

 metric negativity in that of electrical response. It will also 

 be seen that when secondary disturbing causes are removed, 

 the response to gravity is immediate, showing that there is 

 no anomalous delay between the displacement of the hypo- 

 thetical particles and the consequent response. By now 

 rotating the specimen back through 90, the action of gravity 

 is virtually removed. The after-effect persists for two 

 minutes, and after this the response curve shows the usual 

 recovery. 



