642 



ELECTRICAL MEASUREMENTS 



to charge it and to charge the condenser multipliers which are 



used at very high voltages. 



In the instrument devised by Ho and Koto, Fig. 403, the poten- 



tial to be measured is applied between the plates, FI and F 2 , 



either directly, or through a con- 

 denser multiplier if the voltages are 

 very high. These plates serve as 

 " quadrants." They are 9 mm. 

 wide and 15 mm. long, are exactly 

 alike and placed 5 mm. apart. The 

 mirror m is observed through one 

 of the openings, Wi, the other open- 

 ing, wz, being added in order that 

 the arrangement may be sym- 

 metrical. 



The condensers, Ci and C 2 , serve 

 to split the potential which is ap- 

 plied between the "quadrants." 

 They are nominally of the same 

 capacity; one of them must be 

 adjustable. The condenser multi- 

 plier is introduced by the inser- 

 tion of the condenser, C. 



FIG. 403. Diagram of elec- 

 trostatic oscillograph of Ho and 

 Koto. 



The moving members, or "needles," are formed by two metal 

 strips, Si and 82. As in the ordinary oscillograph they are 

 stretched by a spring, q, between insulating bridge pieces. They 

 are insulated from each other at their lower ends by the silk 

 thread gph. The "needles" are charged from a 300- volt battery 



FIG. 404. Pertaining to demonstration for electrostatic oscillograph. 



of dry cells, B. The middle of the battery is connected to the 

 point d, between the condensers Ci and C 2 . 



Suppose the electrometers to be perfectly symmetrical; the 

 arrangement is that shown in Fig. 404. Consider a fall of poten- 

 tial to be positive in the direction of the arrow. Let e be 



