1876.] On Contact Electricity between Non-Conductors. 169 



determining to a certain extent the general direction of the isoclinal lines 

 by graphic projection. 



The observations are arranged in two tables — Table I. recording those 

 taken during the outward and homeward voyages to and from Singapore, 

 and Table II. containing those made in the eastern seas from Singapore 

 up to Mcolaevsk on the Eiver Amur. They are arranged in order of the 

 latitudes of the places visited; but in aU cases where the observations 

 have been subsequently repeated at the same station, all those taken at 

 the same place are noted in the Table in succession. 



Finally, the author has added a few remarks suggested by a comparison 

 of these observations with those formerly taken by him during his pre- 

 vious visits to China and Japan, 1857-59. 



XX. ^^Experiments on Contact Electricity between Non-Con- 

 ductors.-'^ By Joseph Thomson^ Student at the Physical 

 Laboratory of Owens College. Communicated by B. Stewart, 

 F.R.S. Received May 23, 1876. 



It was observed that when a plate of copper was lifted from a plate of 

 glass the copper was electrified, and also that when a plate of glass was 

 lifted from a plate of wax the glass was electrified, care being taken to 

 have as little friction as possible ; it was afterwards found that the former 

 experiment had already been made by Eechner (see Wiedemann's ' Gal- 

 vanismus,' page 21), who also tried lifting copper from sulphur and got 

 the same effect ; although the plates were lifted as carefully as possible, 

 yet it was not certain that friction had been entirely got rid of, so the 

 following experiments were made to show that there is an electrical dis- 

 placement when two non-conductors or a conductor and a non-conductor 

 are put in contact without friction. 



The arrangement used was as foUows : — 



Grlass rods, AB, CD, EE, G-H, were fixed in a wooden frame ACGrE ; 

 round these rods silk threads, BE, DH, were wound ; an aluminium needle 

 carrying a mirror, M, was hung by a silk thread from a brass rod, T, 

 fastened in the wooden frame ; a wire from the needle dipped into a glass 

 vessel, N, containing sulphuric acid ; a small magnet was fastened to the 

 back of the mirror, and a glass case was placed over the whole; outside 

 the glass case were magnets, by means of w^hich the position of the 

 needle was regulated ; a wire also from the outside dipped iuto the 

 vessel N, and was used to charge the needle with electricity ; positive 

 electricity was got from an ordinary electrophorus, negative from an 

 electrophorus in which the resin was replaced by a plate of glass which 

 was excited by silk. If wax and glass were the substances experimented 

 on, a cake, OQEP, was made, one half of which, OSQ, was glass, the 

 other half, BPS, beiug wax ; the junction of the wax and glass was parallel 



VOL. XXV. N 



