362 



SCIENCE. 



[N. S. Vol. VII. No. 168. 



to the classification of substances as electrics 

 and non- electrics. The true significance of 

 Gilbert's observations as to the effect of 

 moisture was not appreciated for a long 

 time. Gilbert's list of electrics was added to 

 by a number of other observers, prominent 

 among whom were Boyle and Newton. The 

 fact that light and sound accompany elec- 

 tric excitation was called attention to by 

 Otto von Guericke, who also showed that a 

 light body after being brought into contact 

 with an electrified body was repelled by it. 

 Coming now to the 18th century, we find 

 Hawkesbee in 1707 and Wall in 1708 spec- 

 ulating on the similarity of the electric spark 

 and lightning. Then comes one of the most 

 prominent experimenters of this century — 

 Stephen Gray — who began to publish in 1720 

 and who in 1729 found that certain sub- 

 stances would not convey the charge of an 

 electrified body to a distance. - These experi- 

 ments were the first to introduce the distinc- 

 tion 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 dis- 

 covery that the charge of an electrified 

 body is proportional to its surface, and this 

 was afterwards confirmed by the experi- 

 ments of Le Monnier. Many of Gray's 

 experiments were repeated and extended by 

 Du Fay, who found that all bodies could 

 be electrified by friction if they were held 

 by an insulatory substance. Then came 

 the improvements of the electric machine 

 by Boze and "VVinckler ; the firing of in- 

 flammatory 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 fol- 

 lows one of the periods of exceptional ac- 



tivity in electrical research. A party of 

 the Royal Society, with Watson as chief 

 operator, made a series of experiments hav- 

 ing 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 com- 

 plete the circuit in Leyden jar discharges. 

 They concluded that when two observers 

 connected by a conductor, and at, say, two 

 miles apart, obtained a shock by one touch- 

 ing 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 con- 

 cluded that the transmission was practically 

 instantaneous. Watson had ideas as to 

 electric fiuids similar to those which were 

 afterwards systematically worked out by 

 Franklin. A great many curious and in- 

 teresting experiments were made about this 

 time, as, for example, the influence of elec- 

 trification on the flow of water through 

 capillary tubes as discovered by Boyle, the 

 experiments of Mowbraj^ on the eifect of 

 electrification 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 considerable attention 

 from eminent authorities in recent years, 

 and that of the efiect of electrification on 

 the growth and composition of vegetable 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 18th century. Franklin's 

 experiments were begun about the middle 

 of the year 1747, and seem to have been in- 



