January 25, 1894-] 



NA TURE 



29; 



lakes, except when the movements were unusually rapid or ex- 

 tensive, the argument from geographical distribution fails ; for 

 we have no evidence to show whether rock basins are more 

 or less abundant in regions that have been glaciated, than 

 in those that have not ; and seeing, further, that differential 

 movements are known to take place, while it has never been 

 proved that a glacier is physically capable of excavating a rock 

 basin, the onus prohandi rests with the advocates of the glacial 

 theory ; and until they have shown that rock basins are less com- 

 mon in regions that have been glaciated than in those that have 

 not, this argument is not logically admissible. Observations on 

 this point are very desirable, but it must be remembered that 

 filled up lake basins are not the only thing to be looked for ; what 

 is desired is evidence of the production of rock basins, or of such 

 differential movements as would have led to their formation, had 

 the erosion of the barrier been less rapid. In the Himalayas 

 such rock basins appear to have been formed in quite as great 

 abundance as in the mountains of Europe, and to correspond with 

 them in position and form ; but the elevation of the mountains 

 has been so recent, and the rainfall is so great, that the processes 

 of nature are more rapid than in Europe, and the rock basins 

 have consequently not only been filled up, but the barrier has 

 afterwards in many cases been destroyed, and the deposits largely 

 removed by erosion, so that the fact of their having originally 

 been accumulated in a rock basin is not always easily recog- 

 nisable. 



The one new argument of Dr. Wallace's is that derived 

 from .he supposed difference between the outlines of existing 

 lakes and those that would result from the submergence of 

 river valleyb. In the selected instances, however, he has com- 

 pared mountain lakes with submerged lowland valleys instead 

 of with mountain valleys. In the latter, long stretches are 

 frequently found where the slopes of the beds of the side 

 streams are much steeper than that of the main valley ; these 

 valleys if submerged would give rise to lakes of great length 

 in comparison with their breadth, and without the numerous 

 deep embayments of the shore line which would be usually 

 found in a submerged lowland valley. As a single easily 

 verified instance to show that a submerged mountain valley 

 need not have numerous deep bays, I may instance the Pangong 

 lake in the Himalayas, which will be found on any good map 

 of India, and is nothing more than a submerged subaerially 

 formed river valley; on a smaller scale the Malwa Tal near 

 Naini Tal and the Pil lake in the hills east of Quetta, both of 

 which are river valleys dammed by landslips, have simple 

 outlines without any embayments. The instances I have chosen 

 are from regions where there has not been a great extension 

 of the glaciers, and where the form of the valley before its 

 submergence was entirely produced by subaerial denudation. 



R. D. Oldham. 



On the Change of Superficial Tension of Solid-Liquid 

 Surfaces with Temperature. 



In a recent very interesting communication to the Birming- 

 ham Phil. Soc. {Bir. Phil. Soc. Proc, vol. ix. part i, 1893), 

 upon the effect of a solid in concentrating a substance out of a 

 solution into the superficial film in accordance with Prof. J. J. 

 Thomson's investigation ("Applications of Dynamics to 

 Physics," p. 191), Dr. Gore has quoted an observation of 

 Pouillet's {Annales de Chemie, 1822, vol. xx. pp. 141-162), 

 that when inert powders like silica are mixed with liquids that 

 do not act on them heat is evolved. On the other hand, when 

 the superficial area of contact between a liquid and its gas is 

 increased heat is absorbed. This latter is known to be the 

 case because the superficial tension diminishes with rise of 

 temperature. In the case of the solid-liquid surface being pro- 

 duced, it would appear at first sight to follow that the super- 

 ficial tension should increase with increased temperature. The 

 matter is, however, somewhat more complicated. When a dry 

 solid is mixed with a liquid we are substituting a solid-liquid 

 surface for a solid-air surface, and from the fact that most 

 liquids soak up into a mass of dry powder, we may conclude 

 that the superficial potential energy of the solid-liquid is less 

 than that of the solid-air surface, i.e. that more work must be 

 done to separate the liquid from the solid than is developed by 

 the air getting at the solid. If these actions are reversible, we 

 may apply the laws of thermodynamics, and conclude that as 

 heat is evolved when the system does work, i.e. when the 

 solid-liquid surface is increased, that it must require more work 



NO. 1265, VOL. 49] 



to separate the solid from the liquid at high temperatures than 

 at low ones, and in the case of silica and water, for instance, 

 that is very much what one would expect from the action of 

 water at very high temperatures on silica. If we could assume 

 that the superficial tension of air-solid were zero, it would 

 follow from this that the superficial tension of a solid-liquid 

 surface is negative, i.e. that there is a superficial pressure, and 

 that the liquid has more attraction for the solid than for its own 

 particles, and that this difference increases with increased 

 temperature, i.e. the superficial pressure increases. 



The whole subject deserves careful investigation and quanti- 

 tative treatment, but the difficulty of measuring the superficial 

 tensions of solid-liquid surfaces seems almost insurmountable, 

 so that it would be very difficult to verify the theory. Perhaps 

 something might be done with finely divided liquids that did 

 not mix, and whose superficial tensions might be measured. 



Trinity College, Dublin. Geo. Eras. Fitzgerald. 



A Lecture Experiment. 



When charcoal, which has been allowed to absorb as much 

 sulphuretted hydrogen as it can take up, is introduced into 

 oxygen gas, the charcoal will burst into flame owing to the 

 energy of the action of the oxygen upon the sulphuretted 

 hydrogen. 



This fact is stated in most text-books on chemistry, but no 

 description that I have ever seen of this experiment is calculated 

 to bring about the effect with certainty. The following is a 

 simple method for illustrating this reaction upon the lecture 

 table, which I have never found to fail : — ■ 



A few grammes (from five to ten) of powdered charcoal are 

 introduced into a bulb which is blown in the middle of a piece 

 of combustion tube about twenty-five centimetres long. A 

 gentle stream of coal gas is then passed over the charcoal, which 

 is heated by means of a bunsen lamp until it is perfectly dry. 

 This point may be ascertained by allowing the issuing gas to 

 impinge upon a small piece of mirror, and when no further 

 deposition of moisture takes place the charcoal may be con- 

 ! sidered to be dry, and the heating may be stopped. The char- 

 i coal is then allowed to cool in the stream of coal gas until its 

 temperature is so far reduced that the bulb can just be grasped 

 by the hand, when the coal gas is replaced by a stream of sul- 

 phuretted hydrogen. The sulphuretted hydrogen should be 

 passed over the charcoal for not less than fifteen minutes, 

 by which time the bulb and its contents will be perfectly cold, 

 and the charcoal will have saturated itself with the gas. (In 

 practice it will be found convenient to prepare the experiment 

 to this stage, and allow a very slow stream of sulphuretted 

 hydrogen to continue passing through the apparatus until the 

 experiment is to be performed. ) The supply of sulphuretted 

 hydrogen is then cut off, and a stream of oxygen passed through 

 the tube. Almost immediately the charcoal will become 

 hot, and moisture will be deposited upon the glass. The supply 

 of oxygen should be sufficiently brisk to carry the moisture 

 forward from the charcoal, but not so rapid as to prevent 

 it from condensing on the glass tube beyond the bulb. In 

 a few moments the temperature of the charcoal will rise to 

 the ignition point, when it will inflame and continue to burn 

 in the supply of oxygen. G. S. Newth. 



Royal College of Science, London. 



PIERRE JOSEPH VAN BEN EDEN. 



THIS distinguished Belgian zoologist was born on 

 December 19, 1809, at Malines, in the province of 

 Antwerp, a town once well known for its extensive manu- 

 facture of lace. He received an excellent education, and 

 early showed a decided taste for natural history ; his native 

 town being built on the borders of a tidal river, his attention 

 was soon called to the examination of the littoral fauna 

 of Belgium, though it will be remembered that Belgium 

 only evolved itself into a kingdom in the year 1830, 

 when Beneden came of age. His first promotion was 

 to the keepership of the Natural History Collections at 

 Louvain, and in 1835 he was made an assistant professor 

 in the University of Gand, a post which he appears to 

 have held for only one Term, as we find him in the same 



