MAGNETISM AND ELECTRICITY 



40! 



Where great sensitiveness is not required, a perpendicular 

 glass dial and multiplier coil arranged as in fig. 220, which 

 represents one constructed by Stohrer of Leipzig, will be far the 

 most convenient and simple, needing only to be placed in front 

 of the condensers and focussed. 

 With care in balancing the 

 needle, this arrangement can be 

 made amply sensitive for all 

 ordinary induction or direct 

 current experiments, and also 

 serves to illustrate the action of 

 the needle telegraph. 



Another good galvanometer 

 of this kind, shown in fig. 221, 

 was constructed, and has been 

 used with success in many of his 

 lectures to large audiences, by 



Prof. S. P. Thompson. Here the coil A B c D is wound hori- 

 zontally, and to the centre of the needle N s is attached, at right 

 angles, a very light perpendicular index or pointer, the needle 

 and its pointer being so mounted that the centre of gravity 



FIG. 220. Lantern Galvanometer 



Fia. 221. Lecture Galvanometer 



is very little below the pivot E. Long or short coils may be 

 used, and this pattern has the great advantage that it may be 

 used as an ordinary lantern slide. 



In using any kind of ' face ' galvanometer, should the face 



D D 



