563 
of Edinburgh , Session 1877-78. 
caused by the wheel could be heard quite distinctly all over the 
room. Evidently the effect of bringing the horizontal iron bars on 
the circumference of the wheel rapidly in front of the core of the 
proximal telephone was to intensify the currents of the telephones. 
The currents were so strong that a disk held in front of the core of 
the distal telephone could be felt vibrating by the hand. 
The following Gentlemen were duly elected Fellows of the 
Society : — 
James Alfred Ewing, 22 India Street. 
Rev. John Wilson, M.A., Bannockburn Academy. 
Robert Macfie Thorburn, Uddevalla, Sweden. 
Andrew Peebles Aitken, Sc.D., 16 Gillespie Crescent. 
John Milne, Mechanician, Trinity Grove, Edinburgh. 
Monday , 18 th February 1878. 
Sir WILLIAM THOMSON, President, in the Chair. 
The following communications were read : — 
1. The application of the Graphic Method to the determina- 
tion of the efficiency of a direct-acting Steam-Engine. 
By Professor Fleeming Jenkin. 
2. On the Disruptive Discharge of Electricity. By Alex- 
ander Macfarlane, M.A., B.Sc. Communicated by Pro- 
fessor Tait. 
(Abstract.) 
Last summer session, with the assistance of Messrs Salvesen, 
Connor, and Stewart, I applied the method of measuring great 
differences of potential, described in a paper by Mr Patou and my- 
self (Proc. Feb. 19, 1877), to investigate the laws of passage of the 
electric spark. The method essentially consists in connecting the 
prime conductor of the Holtz machine, not with the electrometer 
directly, but with an insulated spherical ball. This ball acts 
