278 SCIENCE OF COMMON THINGS. 



Positive and negative electricity. Velocity of electricity. 



fluid, equally distributed throughout nature : every 

 substance being so constituted as to retain a certain 

 quantity of this agent. Any disturbance of the natural 

 state of a body produces evidences of electricity. 



ISOT* Does electricity seem to exist in two different states or conditions f 



It does ; and to designate these two conditions, the 

 terms positive and negative have been employed. Thus 

 a body which has an overplus of electricity is called posi- 

 tive, and one that has less than its natui^l quantity is 

 called negative. 



ISO 8 Do light, heat, and electricity appear to have some properties in 

 common f 



They do / each may be made, under certain circum- 

 stances, to produce or excite the other. All are so light, 

 subtle, and diffusive, that it has been found impossible 

 to recognise in them the ordinary characteristics of 

 matter. Some suppose that light, heat, and electricity 

 are all modifications of some common principle. 



18O9 Why does the fur of a cat sparkle and crackle when rubbed with 

 the hand in cold weatlier ? 



Because the friction between the hand and fur pro- 

 duces an excitation of negative electricity in the hand 

 and positive in the fur, and an interchange of the two 

 causes a spark, with a slight noise. 



1S1O Why does this experiment work best in very cold weather ? 



Because the air is then very dry, and does not convey 

 away the electricity as fast as it is excited ; if the air, 

 on the contrary, were moist, the electricity would be 

 conducted off nearly as fast as it was excited by friction, 

 and its effects would not therefore be so manifest. 



1811 With what velocity is electricity transmitted through good conduc- 

 tors f 



"With a velocity so great that the most rapid motion 

 produced by art appears to be actual rest when com- 

 pared to it. Some authorities have estimated that elec- 

 tricity will pass through copper w r ire at the rate of two 

 hundred and eighty-eight thousand miles in a second 

 of time a velocity greater than that of light. The 



