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LECTURES TO SCIENCE TEACHERS. 



electrometer, of the principle of weighing the attraction 

 between two discs, has remedied both these defects. The 

 absolute electrometers are not very portable, and thus 

 there is not one to be seen in the Loan Collection. These 

 diagrams will, however, I hope, enable you to understand 

 the principles of the instrument. 



If we have two electrified discs attracting each other, their 



t'iG. S. 



radii being two or three times as great as the distance 

 between them, it can easily be shown that there is a region 

 about the middle where the lines of force are sensibly 

 straight lines. And this condition will also be practically 

 realised by such an arrangement as is show r n in Fig. 9. 

 A and B are two insulated electrified plates. In the middle 

 of B a circular hole is cut, which is filled up by a very light 

 movable disc of aluminium, c, borne at the end of the lever L. 



