The Evolution of Electric and Magnetic Physics. 155 



gave a great impetus to the science by the discovery of con- 

 duction. They showed that glass, resin, silk, and other sub- 

 stances were insulators, or impervious to electricity, but that 

 metals and liquids conducted it. They succeeded in trans- 

 mitting electric force to a distance of several hundred feet, 

 and by these experiments laid the foundation for telegraphy. 

 This classification of substances into conductors and non- 

 conductors since their time has not altered in fact, but its 

 principle is better understood. More delicate measurements 

 have since shown that no known solid or liquid body insu- 

 lates perfectly. On the other hand, the best conductors ob- 

 struct to a certain degree the flow of electricity, so that con- 

 duction and insulation are only the limiting attributes of 

 one property common in varying degrees to every descrip- 

 tion of matter. No conducting power has yet been de- 

 tected in dry gases, but it is possible that if an electrified 

 body could be maintained suspended in a gas without any 

 solid or liquid support, such conducting power might be dis- 

 covered. The best solid insulator yet found is dry, spun 

 quartz, glass following next. The best measurements of the 

 conducting power of glass at the temperature of melting 

 ice show that it is inferior to that of silver the best con- 

 ductor in the ratio of one to three followed by twenty- two 

 zeros. 



From the time of Gray and Wheeler a very extraordinary 

 advance was made in electrical science ; the world of science 

 now gave out myriads of electric sparks. Nearly every year 

 brought to light some fresh discovery in electricity. A gen- 

 tleman in Leyden, Holland, tried to see if he could store up 

 electricity in a bottle, and succeeded. The Leyden jar, the 

 properties of which were thus discovered, was firs* intro- 

 duced in 1745, and this not only drew much attention to 

 the subject, but enabled the experimenter to collect and 

 suddenly discharge a greater store of electrical energy than 

 had been previously possible. 



The researches on electricity that made Franklin so fa- 

 mous came next, and were made between 1747 and 1760. 

 In that time he added greatly to the knowledge of the sub- 

 ject. He proved at Philadelphia that lightning was an elec- 

 tric spark. Lightning had been going on since the world 

 began, but it needed the brightest human intelligence to 

 discover that lightning was electricity. It needed even more 

 than that it needed evolution. Franklin erected the first 

 lightning conductor for the protection of buildings, and 



