APPENDIX 



157 



one or other of the two galvanometers ; and once established, we 

 may, if desired further, shunt both galvanometers, so as to reduce 

 both deflections in the same proportion. For this reduction, the 

 common shunt is to be connected with the terminals on each side 

 of plug No. i. 



,SL 



FlG. 58. Galvanograph. 



The most convenient arrangement of the two galvanometers is 

 shown in Fig. 58, in which G x is the indicator and G 2 the recorder, 

 The two galvanometers are controlled simultaneously by plug No. i, 

 separately and individually by plugs No. 5 and 6 of a secondary key- 

 board. We are therefore able to adjust compensation and make 

 any necessary preliminary adjustments with the photographing 

 galvanometer short-circuited at No. 6, and therefore undisturbed 

 by manipulations in the remainder of circuit, where we are guided 

 by the indicating galvanometer. For an observation of any duration, 

 both galvanometers are in circuit and simultaneously controlled by 

 plug No. i, and the general progress of a record on G 2 in the dark 

 room, can be followed on the scale of G : placed in front of the work- 

 table. 



The accessory apparatus, containing the sensitive plate, consists 

 in a box, -| metre in height, which carries the scale, and the horizontal 

 slit, \ mm. in width, upon its anterior surface. The plate, which is 



