444 



NATURE 



{March 7, 188.9 



the case, something might be done to improve the drainage 

 of the marshes to the east of London. 



Presuming that dark fogs are principally due to smoke, 

 —and Sir Douglas Galton, in a paper read at the Parkes 



• Table III. — Fog Observations from November \, 1887, to 

 March 31/1888. 

 Note. — Two spaces will be found below for every day during the five 

 months. When, owing to the prevalence of fog, artificial light is used on a 

 pafticular day, put a x in the Jirst space assigned to that particular day ; 

 and in the second space put the quarters of an hour or number of whole hours 

 and quarters during which light is used. 



Grand total = 113 hours. 

 Table IV. — Observations taken in Provincial Towns. 



Museum in 1887, on "The Cause and Prevention of 

 Smoke," declared that black (or dark) fog was etitirely 

 the result of smoke, while Dr. Marcet attributes the density 



' Fog not dense on March 23, but very dark. 

 . ^Darkness, rather than fog, from 2.45 to 3.4*. 

 3 Fog and darkness. 



of London fog mainly to smoke — it is clear that we want 

 legislation to intervene, and to extend the Metropolitan 

 Acts of Parliament, viz. those of 1853 and 1856, and 

 instead of allowing these Acts to deal only partially with 

 factory smoke, to cause them to be applied to every 

 house in London. 



It is not necessary to quote any figures here, to prove 

 how the death-rate in London rapidly increases during 

 the prevalence of smoke fogs, as everyone knows it too 

 well. But we may give an extract from the Gas World 

 to show the enormous and quite unnecessary cost of these 

 smoke fogs. 



The Gas World says that, " during the foggy days 

 which were experienced between the i6th and 24th of 

 November 1887, the Gas Light and Coke Company sent 

 out to its customers in London no less than 710,251,000 

 cubic feet of gas ; that to manufacture this quantity 71,000 

 tons of coal must have been carbonized, and that the total 

 value of the gas, without the consideration of the by- 

 products, is ^106,000. During the nine days, therefore, 

 the public paid the Gas Light and Coke Company no 

 less than ^490 per hour for artificial light.''' 



This calculation, it should be observed, does not 

 include the amount supplied by other Gas Companies in 

 London during the same short period of fog. 



W. Hargreaves Raffles. 



ELECTRICAL STRESS.^ 



'X'HE 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 Ger- 

 many, 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 de- 

 monstrated to audiences of a considerable size. Before 

 discussing this portion of his subject the lecturer intro- 

 duced it by an explanation of principles on which the 

 experiments are founded. 



Magnetic lines of force can easily be mapped out by 

 iron filings, but the exhibition of electrical Hnes 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 re- 

 fracting liquid phenyl thiocarbamide appears to be 

 specially suitable for experiments on this subject. If 

 an electrified point is brought over the surface a dimple 

 is formed which becomes deeper as the point approaches 

 it. At the instant at which the needle touches the liquid 

 the dimple disappears, 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 

 whiqh are produced in the fluid in its neighbourhood. 

 When the needle is withdrawn a small column of liquid 

 adheres to it. This effect is, however, seen to greater 

 advantage if a small sphere about 5 mm. in diameter is 

 used instead of the needle-point. When this is withdrawn 

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

 diameter is formed between the sphere and the surface. 

 A similar experiment was made by Faraday on a much 



I Abstract of a Lecture delivered ; 

 by Prof. A. W. Riicker, F.R.S. 



the Royal Institution on February 15, 



