Electricity. 325 



pel it. This quality, called electricity, has been imparted to the paper 

 by the rubbing, and is, in fact, a new form of energy derived from the 

 energy of the rubbing. When the visible motion of the rubbing has 

 ceased, its equivalent in energy persists in the form of heat and elec- 

 tricit}'. Electricity, therefore, as well as heat, is a mode of energy. 

 And this may, in the case of either, be energy in action or, when re- 

 strained, simply energy of position. There are several conditions in 

 which electricity is commonly said to exist, such as current, positive, 

 negative and neutral. Positive and negative are sometimes spoken of 

 as two separate "fluids;" and they were also formerly designated as 

 "vitreous " and "resinous. " When a glass rod is rubbed with silk the 

 vitreous or positive electricity is accumulated on the glass, and the silk 

 becomes negative. If a stick of sealing wax be rubbed with silk, nega- 

 tive or resinous electricity accumulates on the sealing wax, while the 

 silk becomes positive. Electricity becomes current when the body in 

 which it is generated is connected with the earth or with any neutral 

 body, the current leaving the body in which it is generated at the posi- 

 tive and negative ends. An electrical machine, of the frictional kind, 

 having its prime conductor connected with the earth by a chain, will 

 give off a constant current of positive electricity while it is being worked. 

 But it will likewise give off a current of negative electricity flowing to 

 the ground. If there be no outlet from the prime conductor the posi- 

 tive electricity is collected upon it in a state of strain or tension, while 

 the negative is conducted off in a current to the ground. A state of 

 tension is a condition of potential energy, like a spring wound up. 

 The mechanical motion which is arrested b}^ the friction of the rubber 

 on the glass of the machine is the origin of the electrical energy in this 

 case. There is a strict analogy between the potential of gravitation and 

 that of magnetism and electricity. As before remarked the potential of 

 gravitation is the hight to which a body is raised, and the potential en- 

 ergy is measured by the amount of work it would require to raise it to 

 such hight. "If a common bar magnet be taken in the hand and 

 moved near a powerful fixed magnet, work will be done. If like poles 

 are near each other a force of repulsion is exerted and the muscles are 

 called upon to do work in bringing the magnet nearer to the fixed mag- 

 net, moving it against this force." 1 The position to which the magnet 

 is moved in this way by muscular work, is a position of potential en- 

 ergy. And if the magnet be released ( provided it is not allowed to 

 turn end for end ) it will be repelled with an active energy exactly equal 

 to that which was expended in moving it up. The positive poles of two 

 magnets repel each other, and so do the negative poles but the posi- 

 tive poles attract the negative, and vice versa. If force be used to sep- 

 1 Electricity and Magnetism, J. B. Murdock. 



