1902.] accompanying Mechanical Disturbance in Metals. 279 





Permanent 

 current. 



Current of 

 response. 



























Current of response is always towards the more excitable point. 



Detection of Traces of Physico-chemical Clumge. 



I will now describe an experiment which will show in a striking 

 manner how exceedingly delicate is the method of electric response 

 to stimulation, and how by its means we can detect and measure traces 

 of physico-chemical changes in different parts of the same solid. Take 

 a wire and touch two points, one with Na 2 C0 3 solution the other with 

 oxalic acid. Wash the wire. There is no trace left of the previous 

 treatment. Let one contact be permanently made at a normal or pre- 

 viously unacted point N. Let the other exploring contact be moved 



Fig. 3. — Electro-molecular Explorer. 



