406 Professor A. W. Bucher [Feb. 15, 



WEEKLY EVENING MEETING, 



Friday, February 15, 1889. 



William Ceookes, Esq. F.E.S. Vice-President, in tbe Chair. 



Professor A. W. Eijcker, M.A. F.Pt.S. 3LB.L 



Electrical Stress. 



The subject of the discourse was brought before the members of the 

 Royal Institution some years ago by Mr. Gordon. In the interval a 

 considerable amount of work has been done upon it, both in England 

 and Germany, and many experiments have been devised to illustrate 

 it. Some of the more striking of these, though of great interest to 

 the student, are rarely or never shown in courses of experimental 

 lectures. The lecturer and Mr. C. V. Boys, F.R.S., last year devised 

 a set of apparatus which has made the optical demonstration of 

 electrical stress comparatively easy, and most of the results obtained 

 by Kerr and Quincke can now be demonstrated to audiences of a 

 considerable size. Before discussing this portion of his subject the 

 lecturer introduced it by an explanation of principles on which the 

 experiments are founded. 



Magnetic lines of force can easily be majiped out by iron filings, 

 but the exhibition of electrical lines of force in a liquid is a more 

 complex matter. In the first place, if two oppositely electrified 

 bodies are introduced into a liquid which is a fairly good non- 

 conductor, convective conduction is set up. Streams of electrified 

 liquid pass from the one to the other. The highly refracting liquid 

 phenyl thiocarbamide appears to be specially suitable for exi^eriments 

 on this subject. If an electrified point is brought over the surface a 

 dimjjle is formed which becomes deeper as the point approaches it. 

 At the instant at which the needle touches the liquid the dimple dis- 

 appears, but a bubble of air from the lower end frequently remains 

 imprisoned in the vortex caused by the downward rush of the 

 electrified liquid from the point. It oscillates a short distance 

 below the point, and indicates clearly the rapid motions which are 

 produced in the fluid in its neighbourhood. When the needle is 

 withdrawn a small column of liquid adheres to it. This efiect is, 

 however, seen to greater advantage if a sphere about 5 mm. in 

 diameter is used instead of the needle-point. When this is with- 

 drawn a column of liquid about 5 mm. high and 2 mm. in diameter 

 is formed between the sphere and the surface. A similar experi- 

 ment was made by Faraday on a much larger scale with oil of 

 turpentine, and he detected the existence of currents which are in 

 accord with the view that the unelectrified liquid flows up the exterior 



