bs 0880) 
XXIII.—On the Disruptive Discharge of Electricity: An Experimental Thesis 
Jor the Degree of Doctor of Science, Department A. By ALEXANDER 
MacrarLane, M.A., B.Sc. (Plate XXII) 
(Read 18th February 1878.) 
The experiments to which I shall refer were carried out in the physical 
laboratory of the University during the late summer session. I was ably 
assisted in conducting the experiments by three students of the laboratory,— 
Messrs H. A. SAtvesen, G. M. Connor, and D. R. Stewart. The method 
which was used of measuring the difference of potential required to produce a 
‘disruptive discharge of electricity under given conditions, is that described in a 
paper communicated to the Royal Society of Edinburgh in 1876 in the names 
of Mr J. A. Paton, M.A., and myself,* and was suggested to me by Professor 
Tait as a means of attacking the experimental problems mentioned below. 




The above sketch which I took of the apparatus in situ may facilitate the 
description of the method. The receiver of an air-pump, having a rod capable 
of being moved air-tight up and down through the neck, was attached to 
one of the conductors of a Holtz machine in such a manner that the con- 
ductor of the machine and the rod formed one conducting system. Projecting 
_ from the bottom of the receiver was a short metallic rod, forming one conductor 
* “Proc, R.S.E.” vol. ix. p. 332. 
VOL. XXVIII. PART II. 8 B 
