ELECTRICITY. 



deprived of their electricity and reduced to the 

 natural state : but they repel each other again, as 

 soon as the finger is withdrawn, being again elec- 

 trified. 



As all bodies possessed of the same kind of elec- 

 tricity, that is, either all positive or all negative, 

 repel each other in proportion to the superabun- 

 dant quantity they contain, upon this principle, 

 instruments called electrometers are constructed 

 for measuring the degree in which a body is elec- 

 trified. 



Fig. 6. represents Mr. Henley's quadrant elec- 

 trometer ; it may be fixed upon the prime conduc- 

 tor, which generally has a hole in it for that 

 purpose, or upon any other apparatus that may be 

 thought necessary. It consists of a very light rod, 

 and pith ball, A, turning on the centre of a semi- 

 circle B, so as always to keep almost close to its 

 graduated limb, c is the pillar that supports the 

 semicircle and rod. The whole instrument may 

 be made of wood or ivory ; but is found most per- 

 fect when the pillar and index, or rod, are made of 

 box, and well smoothed with emery paper, the ball 

 of pith, and the graduated part of the semicircle 

 ivory, as the divisions are more legible than in 

 wood. 



The moment this instrument begins to be elec- 

 trified, the rod is repelled by the pillar, and con- 

 sequently begins to move over the edge of the 

 semicircle, showing to the greatest precision, the 

 degree to which the prime conductor is electri- 

 fied; or how high any jar or battery is charged. 



Bennefs electrometer ', represented Fig. 4., is by 

 far the most delicate of any yet invented, for dis- 

 tinguishing small quantities of electricity. It 



