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LECTURES TO SCIENCE TEACHERS. 



as near as possible without touching, and thus form parts of 

 a cylinder, divided only from each other as it were by two 

 saw-cuts. Thus also they are arranged symmetrically 

 around the needle. One of the four is capable of adjust- 

 ment by a screw turned by a milled bead. Slight motions 

 of this quadrant serve for adjusting the zero of the instru- 

 ment occasionally. 



The quadrants are connected in pairs by fine wires, the 

 opposite quadrants being connected together ; and from one 



Fio. 4. 



quadrant of each pair rises an electrode which passes insn- 

 tated through the top of the lantern. These electrodes serve 

 to connect two conductors, whose difference of potentials 

 is to be measured, one with each pair of quadrants. The 

 third electrode (see Fig. 4), passing up through the top 

 of the lantern, is for charging and discharging the Leyden jar 

 of the electrometer. 



We next come to the " needle." It is a thin flat piece 

 of sheet aluminium, shaped perhaps more like the paddle 



