ELECTRICAL UNITS OF MEASUREMENT. 127 



conductivity, and they both languished for the 

 want of a name. My own pupils will go on using 

 the resistance box in ohms, rather than the con- 

 ductivity box, because in using the latter it is so 

 puzzling to say " The resistance is the reciprocal 

 of the sum of the reciprocals of these resistances." 

 It is the conductivity that you want to measure, 

 but the idea is too puzzling ; and yet for some 

 cases the conductivity system is immensely supe- 

 rior in accuracy and convenience to that by adding 

 resistances in series. For the reciprocal of an ohm 

 in the measurement of resisting power for the 

 unit reckoning of conductivity which will agree 

 with the ohm it is suggested to take a phono- 

 graph and turn it backwards, and see what it 

 will make of the word "ohm." I admire the 

 suggestion, and I wish some one would take the 

 responsibility of adopting it ; we should then have 

 mho boxes of coils at once in general use. With 

 respect to electric light, what is it we want to 

 measure by the current galvanometer ? We have 

 a potential galvanometer, and we have a current 

 galvanometer. Everybody knows what we want 



