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course, very soon seryed 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 electrified body is propor- 
tional to its surface, and this was afterward confirmed by the experiments 
of Le Monnier. Many of Gray’s experiments were repeated and extended 
by Dufay, 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 sub- 
stances, such as alcohol, by means of the electric spark by Ludolph, Gor- 
don, 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 haying for their object the deter- 
mination 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 con- 
nected by a conductor and at, say, two miles apart, obtained a shock by 
one touching the inside coating of a Leyden jar and the other the earth, 
the electric circuit was four miles long; that is, the earth acted as a return 
conductor. They also concluded that the transmission was practically in- 
stantaneous. Watson had ideas as to electric fluids similar to those which 
were afterward 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 capil- 
lary tubes as discovered by Boze; the experiments of Mowbray on the effect 
of electrification on vegetation, and those of the Abbe Monon 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 considerable 
attention from eminent authorities in recent years, and that of the effect 
of electrification on the growth and composition of vegetables is at pres- 
ent attracting attention in the form of systematic investigation. 
The contributions by Franklin are by far the most important which 
mark the middle portion, or indeed any portion, of the eighteenth century. 
