TEANSACTIONS 01' SECTION A. 435 



if we watch the surfaces of flowing rivers, or of tidal currents flowing in narrows 

 or kyles, we may often have opportunity to observe very prevalent indications of 

 rushes of water corning up to the surface and spreading out there. He considers 

 that these proceed from the bottom, being driven upwards in consequence of 

 impulses arising through the scouring action of the current along the bed. Thus 

 the water so arriving to the surface and spreading out there is composed largely of 

 the deadened water from the bottom — deadened as to forward motion by the 

 intense fluid friction at the bottom. The superficial layer, thus always fresh from 

 the bottom, becomes in its turn overflowed by new supplies from the bottom, and so 

 it gradually descends to enter into the middle body of the stream. At the same 

 time it is perpetually under the accelerating influence of the earth's attraction, in 

 Virtue of its downhill flow, and so it attains increase of velocity beyond that which 

 it had at the surface. 



7. Note on the Pecletic Action of Soap* 

 By Professor W. Stanley Jevons, F.B.S. 



Since the publication, in the ' Quarterly Journal of Science,' for April 1878, of 

 the author's paper on the so-called Brownian movement of microscopic particles, 

 which he proposes to term Pedesis, it has been suggested that soap would form a 

 good critical substance for experiment in relation to this phenomenon. Soap con- 

 siderably reduces the surface-tension of water, in which it is dissolved without 

 much affecting, as is said, its electric conductibility. If, then, pedesis be due to 

 surface-tension, as some physicists assert, the motion would be killed, or much 

 lessened, when soap is dissolved in the water. The experiment having been tried 

 with china-clay, red oxide of iron, chalk, bariuni carbonate, &c, gave the opposite 

 result; the pedetic motion appeared to be increased and facilitated. A similar 

 result was obtained by experiments upon the suspension of china-clay in dilute 

 solutions of soap ; it w T as found that soap distinctly prevented the precipitation of 

 the suspended powder, and this result was obtained even in the presence of 1 per 

 cent, of sodium carbonate. 



The author believes that these results are in favour of his own opinion that 

 pedesis is a phenomenon of electric origin, and can only go on in liquids of high 

 electric resistance. He also points out that the detergent action of soap is probably 

 due to the increase of pedetic action, which causes particles to become detached 

 and suspended in the soapy liquid. Only in this way can we understand the 

 utility of combining an alkaline salt with stearic or other fatty acid. So far as the 

 action of soap depends on the alkali, it would be more active in the absence of the 

 other constituent, which he therefore infers is only needed to maintain the pedetic 

 and suspensive power of the water. The author believes that this is only one of 

 many phenomena which may be explained by the study of pedesis ; and he pro- 

 poses to follow up the inquiry with regard to several substances tending to increase 

 the motion. 



8. Motions produced by Dilute Acids on some Amalgam Surfaces. 

 By Robert Sabine. 



The author finds, when a drop of very dilute acid is placed upon the clean and 

 newly-filtered surface of a rather rich amalgam of some metal which is positive to 

 mercury, that the drop does not lie still as it would do upon pure mercury, but sets 

 itself into an irregular jerky motion. This is the case with copper, zinc, antimony, 

 tin, and lead amalgams. But if instead of these amalgams, those of platinum, 

 gold, and silver are used — these latter metals being negative to mercury — the drop 

 of acid water lies quite still. The acids tried were : sulphuric, hydrochloric, 

 oxalic, and acetic, which behaved similarly, but in different degrees. 



When the experiment is made in an atmosphere of oxygen, the movements 



* Printed in the ' Quarterly Journal of Science ' for October 1878, vol. viii. N.S. 

 p. 514 ; and in ' Nature.' August 22, 1878, vol. xviii. p. 440. 



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