Electrical Phcenomena. 113 



struck by them ; and the clappers then becoming, 

 in their turn, electrified, will be repelled by these 

 bells, and attracted by that which is in the mid- 

 dle, and their electricity will be then attracted 

 away by the chain which passes to the floor. 

 After this the clappers will be again attracted by 

 the outermost bells, and thus the ringing will be 

 continued as long as the conductor is charged. 

 An apparatus of this kind is usually attached to 

 the conducting rods, which are fixed to the 

 gable-ends of houses to protect them from light- 

 ning, and thus serve to give notice of a thunder 

 storm. 



The instrument called an electrometer (fig. 

 36.), which is commonly used for measuring 

 the quantity of electricity contained in any body, 

 is constructed on a similar principle. It consists 

 of a vertical stem L M which terminates in a 

 round top L like a ball. It may be fixed in one 

 of the holes of the conductor, or at the top of a 

 Leyden phial. , To the upper part of the stem a 

 graduated semicircle is fixed, as well as the index, 

 which consists of a very 'slender piece of wood, 

 which reaches to the centre of the graduated 

 arch, and at its extremity there is a small pith 

 ball. When the body is electrified, the index 

 recedes more or less from the pillar, and the de- 

 gree is ascertained by the gradations on the arch. 



Electricity accelerates the evaporation of liquors 

 and the perspiration of animals. There is reason 

 also to apprehend that it is not without effect 



