596 



NATURE 



{April 2\, 18.S7 



GEOGRAPHICAL NOTES 



The new volume (xi.) of the Gcographisches yahrbucli, edited 

 by Prof. Hermann Wagner, begins a new series, and assumes a 

 new form. It has been elongated from the small square form 

 with which we have been familiar, into a respectable octavo, 

 containing about 500 pages. Moreover the present volume is 

 entirely devoted to what in former years was only a section : an 

 account of progress in the various departments into which 

 scientific geography is divided. The next volume will no doubt 

 contain memoirs on various subjects of geographical interest. 

 The subject of physical geography (or rather geophysics) is 

 treated by Dr. Hergesell and Dr. Rudolph. Prof. Toula deals 

 with the investigations of the last four years in the geognostic 

 structure of the earth's surface in all parts of the world. The 

 progress of oceanography is of course dealt with by the great 

 authority on the subject, Dr. O. Kriimmel, while Dr. Hann 

 does a similar service for geographical meteorology, or climate. 

 Botanical geography is treated by Dr. Oscar Drude, and 

 zoological geography by Dr. L. K. Schmarda. Dr. G. Gerland 

 gives the results of research in ethnology during 1884-86 in the 

 various quarters of the globe. ' Under Dr. Wagner's sole 

 editorship the Jahrbitch is becoming more valuable than ever as 

 a book of reference in scientific geography. 



The Rev. George Grenfell, the explorer of the Mobangi and 

 other important tributaries of the Congo, has arrived in London. 

 Unfortunately his health is by no means satisfactory, and it will 

 be necessary for him to rest for some time, therefore his appear- 

 ance at the Royal Geographical Society must be delayed. He 

 has brought home with him his original maps, which are admir- 

 able specimens of such work. They are on a scale of about 

 5 inches to a mile, and are evidently plotted with the greatest care ; 

 his work is therefore likely to take a high place. Dr. Lenz, who 

 has .arrived in Vienna, it is hoped will be in London at the end 

 of this month, and as Dr. Junker may be here about the same 

 time, it is just possible that both these eminent explorers 

 may appear together at the first meeting of the Geographical 

 Society in May. 



Under Colonel Woodthorpe, the work of surveying our 

 new Burmese territory is proceeding apace. Up to the end of 

 January the out-turn of work amounted to 800 square miles on 

 the }-inch, and 260 miles on the ^-inch scale. 



The narrative of Baron Nordenskjdld's memorable journey 

 into the interior of Greenland in 1883, is now appearing in 

 instalments in the German journal Globus, profusely illustrated. 



Two Expeditions are being sent out by the Russian Geogra- 

 phical Society this year : one, under J. P. Kusnetzow, to 

 investigate the flora of the Northern Urals ; and another, under 

 Prince Massalsky, to continue his Transcaucasian researches, 

 which include both botany and ethnography. 



VALENCY AND RESIDUAL AFFINITY- 



n. 



JlfETALLIC CONDUCTION.—! do not propose in any way 

 to discuss metallic conduction, but merely to call attention 

 to some of the analogies between it and electrolytic conduction. 

 It is conceivable, and it would appear probable from the 

 fairly regular manner in which the electrical resistance of most 

 pure metals decreases as the temperature falls, the coeffi- 

 cients of change being practically very nearly the same in all 

 cases, that the increase in resistance as temperature rises is 

 mainly due to the increase in molecular inter-distances. As a 

 rule, resistance increases on the passage of a metal from the 

 solid to the liquid state, but there are noteworthy exceptions 

 from which it would appear probable that even in pure metals 

 conductivity to some extent depends on molecular composition : 

 thus the conductivity of bismuth increases at the moment of 

 fusion from 0-43 to 073 of that of mercury at 31°, and that of 

 antimony from 0-59 to 0-84 (L. de la Rive, Comt. rend., 1863, 

 Ivii., p. 691) ; It is well known that bismuth contracts consider - 

 ably on fusion, and this is probably also the case with antimony. 

 Again, according to Bouty and Cailletet (ibid., 1885, c, p. 

 1 188), the resistance of mercury decreases at the point of solidi- 

 fication in the ratio 4-08 : i ; this is a remarkable increase in 



' Revision and extension of a paper by Prof. H. E.Armstrong, F.R.S., 

 communicated to the Royal Society last year. Continued from p. 572. 



conductivity, and it is difficult to believe that it is wholly due tu 

 mere contraction of volume. 



That the behaviour of alloys is worthy of far more attention 

 than it has hitherto received appears most clearly from the few 

 data at disposal. I would specially call attention to the curve 

 given by Prof. Lodge as representing the specific conductivities 

 of the copper-tin alloys (Phys. Soc. Proc, 1879-80, iii., p. 158). 

 The general resemblance of this curve to that given by F. Kohl- 

 rausch for mixtures of sulphuric acid and water appears to me to 

 be in the highest degree suggestive. 



Valency — Chemical Chunge. — Notwithstanding the fierce con- 

 troversy which has been waged between the .advocates of the 

 doctrine of fixed valency, our views on the subject are still in an 

 unfortunate degree unsatisfactory and indefinite. Even those — 

 and they probably form a large majority — who regard valency as 

 a variable, dependent both upon the nature of the associated 

 radicles and the conditions — especially as to temperature — under 

 which these are placed, often hesitate to attribute a valency suf- 

 ficiently high to account for every case of combination ; in fact, 

 both parties agree in distinguishing "atomic" from "molecu- 

 lar" compounds, and differ only as to where the line shall be 

 drawn. 



It is difficult to over-estimate the importance of the theory of 

 valency : its application has led to an enormous extension of our 

 knowledge of carbon compounds especially, and it has furnished 

 us with a simple and consistent system of classifying the mighty 

 host of these bodies ; but, on the other hand, it may be ques- 

 tioned whether it has not led us away from the search into the 

 nature of chemical change, and even if the introduction of the 

 terms saturated and unsaturated has not had a directly pernicious 

 effisct. The almost universal disregard of molecular composition 

 as an important factor in chemical change in the case of solids 

 and liquids, and the popular tendency to overlook the fact that 

 our formulae of such bodies are purely empirical expressions, has 

 undoubtedly exercised a prejudicial influence. 



No known compounds are saturated : if any were, such would 

 be incapable, I imagine, of directly taking part in any inter- 

 action, and in their case decomposition would necessarily be a 

 precedent change. The paraffins are apparently, of all bodies, 

 the most inert and the most nearly saturated,' and next to them 

 comes hydrogen — the unsaturated character of which is dis- 

 played in interactions such as occur at atmospheric temperatures 

 Ijetween it and platinum and palladium, and when it displaces 

 silver from silver nitrate or certain of the platinum metals from 

 their salts. One of the most striking instances, perhaps, of 

 popular error in this respect is water, which is always regarded 

 as a saturated compound, although its entire behaviour, and 

 especially its physical properties, characterise the molecule 

 H.,0, I think, as that of an eminently unsaturated compound : 

 I fail to see how, otherwise, we are to explain the high surface- 

 tension and high specific heat of liquid water, its high heat of 

 vaporisation, and its imperfectly gaseous behaviour up to tem- 

 peratures considerably above its boiling-point, let alone its great 

 solvent power and its tendency to form hydrates with a multi- 

 tude of compounds — especially oxygenated compounds, be it 

 added. 



The theory was brought most prominently under the notice of 

 chemists by Helmholtz in the last Faraday Lecture, that electri- 

 city, like matter, is, as it were, atomic, and that each unit of 

 affinity or valency in our compounds is associated with an 

 equiv.alent of electricity — positive or negative ; that the atoms 

 cling to their electric charges, and that these charges cling to 

 each other. Thus barely stated, this theory does not appear to 

 take into account the fact that ihe fundamental molecules, even 

 of so-called atomic compounds, are never saturated, but more or 

 less readily unite with other molecules to form molecular com- 

 pounds — molecular aggregates ; and unless the application of 

 the theory to explain the existence of such compounds can be 

 made clear, chemists must, I think, decline to accept it. The 

 impression which the facts make upon the mind of the chemist 

 certainly is (i) that no two different atoms have equivalent 

 affinities ; and (2) that affinity is a variable depending on the 

 nature of the associated elements : but, owing to the recognised 

 complexity of ne.arly all cases of chemical change, it is difficult 

 to draw any very definite conclusion on this point. 



If, however, the nature and properties of so-called molecular 

 compounds generally be considered, and if an attempt be made 

 to form any conception of their constitution, one striking fact is 



t to place nitrogen first in the list, as being the 



