50 IOWA ACADEMY OF SCIENCES. 



through the coherer and the potential difference between 

 its terminals were read directly. 



For the determination of the behavior under the smallest 

 E. M. F.'s a high resistance, four coil Kelvin galvanometer 

 was used as voltmeter and a similar low resistance instru- 

 ment as ammeter. For larger E. M. F.'s these were 

 replaced in turn by milli voltmeter and millammeter; 

 voltmeter and ammeter. This range of instruments indi- 

 cates the range over which the investigation extended. 



It was my fortune to have the use of one of the filing 

 coherers used by Kinsley in his investigation; a coherer 

 with fixed silver electrodes, with silver filings slightly 

 coated with silver sulphide. The amount of filings in the 

 gap between the electrodes was capable of adjustment. 

 On measuring the current flowing as the E. M. F. was con- 

 tinuously increased, the current was found to increase in 

 such a way as to be represented graphically by a smooth 

 curve. The relation between the E. M. F. and the current 

 depends upon the initial conditions, viz: the amount of 

 filings between the terminals and the pressure upon them. 

 The several curves seem to be related in such a way as to 

 be expressed by the equation. 



i = af(e) - -_- - (1). 

 in which i = current; e = E. M. F. 



a = a variable parameter, depecdinpr upon the initial cotuliiii ns. 



Guthe and Trowbridge give for their results: 



f(e) ^ log (1 - e/E) 

 when E = th« Uiaximum potential difference that can be su-taincd 

 between the terminals of the coherer. 



Measurements were made upon a simpler coherer, con- 

 sisting of a single contact between J inch steel bicycle 

 balls supported in a horizontal glass tube of slightly larger 

 internal diameter. The balls were carried by spiral springs, 

 one of which could be moved along the tube by a micro- 

 meter screw, in order to vary the pressure at the contact. 

 The coherer was carried on an insulating base. This was 

 floated in a vessel of mercury which in turn was floated 

 in a second vessel of mercury. Connections were made 



