NIPHER NEW FORM OF LECTURE GALVANOMETER. 



3S9 



care in winding. By sliding the rods b in or out, the distance 

 betvveen.the coils may be readily varied from 2 cm. to 10 cm., the 

 image of the needle being in all cases perfectly distinct. In this 

 way the instrument is adjusted to currents of any strength. Scales 

 cut in the rods b serve to regulate the distances. 



On the outside of the box are six plates of brass, whose form 

 and arrangement are shown in Fig. 2. The extremities of the 

 coils are connected with the four plates x\, B, C, D. This con- 

 nection may be made by binding-screws on the inside of the box, 

 in which case the coils may be rep aced with ease b}- others of 

 greater or less resistance. The plates may be put in metallic 

 contact by means of brass plugs inserted at a, /?, c, oT, e, g^ h. k. 



IFig. 34.] 



Putting plugs at h and e, and connecting the poles of a galva- 

 nic cup at the binding-screws A and C, the current runs suc- 

 cessively through the two coils R, each causing deflection in the 

 same direction. Let R represent the resistance of one coil, then 

 the galvanometer will have a resistance of 2 R. This arrange- 

 ment is very useful in working with ordinary currents from a con- 

 stant battery. 



If, instead of the former connections, plugs be put at a, </, ^, 

 and /^, the wires from the source of electricity being connected at 

 E and F, then the galvanometer resistance becomes \ R. This ar- 

 rangement is of course to be used with circuits of small resistanee 

 such as thermo-currents. For this kind of work the instrument 

 is thoroughly adapted. 



This instrument can also be used as a diff'erential galvanome- 

 ter. To do this, put the positive pole of the battery at E. Plug 



iii— 19 [Dec. 15, 1875.] 



