218 THE DEVELOPMENT OF ELECTRICAL SCIENCE. 



of an electrified body to a distance. These experiments were the first 

 to introduce the distinction between conductors and non conductors, 

 and, of course, very soon served to explain the reason why certain 

 substances could not be electrified by friction when held in the hand. 

 Gray also made the important discovery that the charge of an electri- 

 fied body is proportional to its surface, and this was afterwards con- 

 firmed by the experiments of Le Monnier. Many of Gray's experi- 

 ments were repeated and extended by Du Fay, who found that all 

 bodies could be electrified by friction if they were held by an insulating 

 substance. Then came the improvements of the electric machine by 

 Boze and Winckler; the firing of inflammatory substances, such as 

 alcohol, by means of the electric spark by Ludolph, Gordon, Miles, 

 Franklin, and others. About this time (1745) the properties of the 

 Leyden jar were discovered by Kleist, Cuneus, and Muschenbroeck, 

 and a few years later it was given practically its present form by Sir 

 William Watson. Then follows one of the periods of exceptional activity 

 in electrical research. A party of the Royal Society, with Watson as 

 chief operator, made a series of experiments having for their object 

 the determination of the distance to which electrical excitation could 

 be conveyed and the time it takes in transit. They found, among other 

 things, that several persons at a distance apart might feel the electric 

 shock if they formed part of a circuit between the electrified body and 

 a conductor, such as the earth; also, that the earth could be used to 

 complete the circuit in Leyden jar discharges. They concluded that 

 when two observers connected by a conductor, and at, say, 2 miles 

 apart, obtained a shock by one touching the inside coating of a Leyden 

 jar and the other the earth, the electric circuit was 4 miles long; that 

 is, the earth acted as a return conductor. They also concluded that 

 the transmission was practically instantaneous. Watson had ideas as 

 to electric fluids similar to those which were afterwards systematically 

 worked out by Franklin. A great many curious and interesting 

 experiments were made about this time, as, for example, the influence 

 of electrification on the flow of water through capillary tubes as dis- 

 covered by Boyle, the experiments of Mowbray on the effect of electri- 

 fication on vegetation, and those of the Abbe Menon on the loss of 

 weight of animals when they were kept electrified for a considerable 

 time. 



The effect of electrification on the flow of water has received consid- 

 erable attention from eminent authorities in recent years, and the effect 

 of electrification on the growth and composition of vegetables is at 

 present attracting attention in the form of systematic investigation. 



The contributions of Franklin are by far the most important which 

 mark the middle portion of the eighteenth century. Franklin's experi- 

 ments were begun about the middle of the year 1747, and seem to have 

 been inspired by the receipt of a Leyden jar from a friend, William 

 Collinson, of London. He propounded the theory of positive and nega- 



