220 REPORTS ON THE STATE OP SCIENCE.— 1915. 



in the increase of conductivity caused by electrical excitation. The 

 value of such increase is expressed in the last column of the protocols 

 as the numerical ratio between the deflections by 001 volt before and 

 after excitation. Thus, e.g., in Observation IV., the deflections as 

 given in columns 2 and 12 are 60 and 80 respectively, and the increase 

 of conductivity is therefore expressed by the fraction fg or 1'33. 



We give below the detailed protocols of typical observations, each 

 consisting of ten tests, and a summary of other observations, each of 

 which also comprised ten tests. 



Column 1 gives the E.M.F. of the accidental current or current of 

 injury of the plant, measured by compensation. The prefixed 

 sign + signifies that its direction in the plant is from B to A. 

 In Observation II. its high value is due to the fact that B 

 is a transverse section, i.e., the seat of known injury. The 

 magnitude of such injury-current is in itself to some extent 

 an indication of the degree of vitality. The blaze-currents 

 (columns 5, 7, 9, and 11) are of opposite direction to the injury- 

 current. 



Column 2 gives in scale degrees the observed magnitude of the 

 galvanometric deflection by 001 volt. Comparison of this 

 deflection with the deflection by 001 volt through 1,000,000 

 ohms indicates the resistance in circuit. 



Columns 3 and 13 give in ohms x 1,000 the resistance in circuit 

 before and after excitation. 



Columns 4 and 6 give in scale degrees the observed magnitudes of 

 the blaze deflections in response to weak-break induction shocks 

 in the + and — directions. 



Columns 5 and 7 give the calculated values of the E.M.F. indicated 

 by the observed deflections of columns 4 and 6. 



Columns 8 and 10 give in scale degrees the observed magnitudes 

 of the blaze deflections in response to strong-break induction 

 shocks in the + and — directions. 



Columns 9 and 11 give the calculated values of the E.M.F. indi- 

 cated by the observed deflections of columns 8 and 10. 



Column 14 gives the relation of the conductivity after excitation to 

 that before excitation taken = 100. Thus the number 133 signi- 

 fies that the conductivity has been increased 33 per 100. 



