A7(o. 27, 1874] 



JVA TURE 



339 



all the equivalents of carbon in it do not belong to the same atom, 

 and the two atoms of carbon are directly united together, and 

 replacement of the equivalents united to one of these atoms does 

 not very greatly affect the function or chemical character of the 

 equivalents united to the other. 



I have perhaps spent too much of your time upon these histo- 

 rical questions. Let us now shortly consider what is the present 

 state of our knowledge as to chemical constitution. This I have 

 already defined as the order in which the constituents are united 

 in the compound. We may indeed use metaphorical language, 

 and speak of the relative position of atoms, perhaps deluding 

 ourselves into the notion that such language is more than meta- 

 phorical ; but the phenomena of combination and decomposition, 

 although we cannot doubt that they depend solely upon tlie rela- 

 tive position and dynamical relations of the atoms, are not alone 

 sufficient to prove even that atoms exist. Our knowledge of the 

 intimate structure of matter comes from another source — from the 

 study of the properties rather than of the changes of substances, 

 and of the transformations of energy which accompany the trans- 

 formations of matter. 



This is strictly a branch of chemistry : the aim of chemistry is 

 to connect the properties of substances and the changes they 

 undergo with their composition, taking this word in its widest 

 sense ; and we must not allow our friends in Section A to cut 

 our science in two and appropriate the half of it. We all frankly 

 admit that chemistry is a branch of physics ; but it is so as a 

 whole — no section of it is more purely physical than all the 

 rest. To accept a narrower definition of chemistry is to reduce 

 ourselves to the position which the collector occupies among 

 naturalists ; it is to admit that it is our business to provide part 

 of the materials out of which a science in which we have no share 

 may be constructed by others. But we need not fear that this 

 so-called physical side of chemistry will ever be divorced from 

 the study ot chemical change. The names of Faraday and 

 Graham among those who have left us, of Andrews among those 

 who are still at work, are sufficient proof of this ; and a study of 

 their researches will conclusively show that great results can 

 be looked for in this direction only from a physicist who is also 

 a chemist. 



There are three special directions in which such investigations 

 h.ive already influenced chemical theory : — i. Ehrtrolysis, which 

 has confirmed the equivalent as a chemical unit, has proved that 

 equivalents unite in pairs, thus forming the basis of electro- 

 chemical theory, and has shown us how to estimate the amount 

 of energy involved in the union of a given pair of equivalents. 

 2. Vapoiir-thiisity, from which Avogadro inferred the law of 

 molecular volumes (since proved by Clerk-Maxwell), which has 

 given us the molecule as a chemical unit, and formed the basis 

 of the unitary theory. 3. Specific Jicat, from which Dulong 

 and Petit inferred their empirical law, which gives us the 

 most satisfactory physical definition of the atom as a chemical 

 unit. 



We naturally turn to the future, and try to guess whence the 

 next gi'eat revolution will come. For although periods of quiet 

 have their use, as affording time for filling up the blank 

 schedules furnished by the last speculative change, such periods 

 have seldom been long, and each has been shorter than its pre- 

 decessor. 



But it is impossible to make a certain forecast : looking back, 

 we see a logical sequence in the history of chemical speculation ; 

 and no doubt the next step wiU appear, after it has been tal<en, 

 to follow as naturally from the present position. One tiling we 

 can distinctly see — we are struggling towards a theory of che- 

 mistry. Such a theory we do not jjossess. What we are some- 

 times pleased to dignify with that name is a collection of 

 generalisations of various degrees of imjjerfection. We cannot 

 attain to a real theory of chemistry until we are able to connect 

 the science by some hypothesis with the general theory of 

 dynamics. No attempt of this kind has hitherto been made ; 

 and it is difficult to see how any such attempt can be made until 

 we know something in reference to the absolute size, mass, and 

 shape of molecules and atoms, the position of the atoms in the 

 molecule, and the nature of the forces acting upon them. Whence 

 can we look for such knowledge ? 



The phenomena of gaseous diffusion, of gaseous friction, and 

 of the propagation of heat through gases, have already given us 

 an approximation to the size and mass of the molecules of gases. 

 It is not unreasonable to suppose that a comparative study of 

 the specific heat of gases and vapours may lead to some approxi- 

 mate knowledge as to the shape of their molecules ; and a com- 

 parison of such approximate results with the chemical constitution 



of the substances may le.ad to an hypothesis which will lay the 

 foundation of a real theory of chemistry. 



Chemistry will then become a branch of applied mathematics ; 

 but it will not cease to be an experimental science. Mathematics 

 may enable us retrospectively to justify results obtained by expe- 

 riment, may point out useful lines of research, and even some- 

 times predict entirely novel discoveries, but will not revolutionise 

 our laboratories. Mathematical will not replace Chemical 

 analysis. 



We do not know when the change virill take place, or whether 

 it will be gradual or sudden ; but no one who believes in the 

 progress of human knowledge and in the consistency of Nature 

 can doubt that ultimately the theoiy of Chemistry and of all 

 other physical sciences will be absorbed into the one theory of 

 Dynamics. 



SECTION E 



Geography 



Opening Address by the President, Major Wilson, R.E. 



The President of the Royal Geograpliical Society has so re- 

 cently delivered his anniversary address, that if I were to attempt 

 to trace the progress of geographical discovery during the period 

 that has elapsed since the meeting of the British Association at 

 Bradford in September last, I could scarcely avoid repeating 

 much that has already been said in far abler terms than I have it 

 within my power to command. Still there are, at the present 

 moment, certain subjects of such very general interest and of so 

 much importance that they cannot well be passed over in any 

 address to the Geographical Section of the British Association. 



It has, I believe, been usual in the addresses to tliis Section to 

 select some special subject for remark, and I will therefore, if 

 you will allow me, before alluding to the geographical achieve- 

 ments of the year, draw your attention to the influence which 

 the physical features of the earth's crust have on the course of 

 military operations ; to the consequent importance of the study 

 of physical geogi'aphy to all those who have to plan or take part 

 in a campaign ; and to the contributions to geographical science 

 that are due, directly or indirectly, to war, .and the necessity of 

 preparing for war. To show how varied are the conditions under 

 which war has to be carried on, and how much its success''ul issue 

 may depend on a previous careful study of the physical cliaracter 

 of the country in which it is waged, it is only necessaiy to remind 

 you of the recent operations on the Gold Coast, brought to a 

 successful issue in an unhealthy climate, and in the heart of a 

 dense tropical forest, where an impenetrable undergrowth, pesti- 

 lential swamps, and deep rivers obstructed the marcli of the 

 troops ; of the Abyssinian expedition, landing on the heated 

 shores of the Red Sea, and thence, after climbing to the lofty 

 frozen highlands of Abyssinia, working its way over stupendous 

 ravines to the all but inaccessible rock, crowned by the fortress 

 of Magdala ; of the march of the Russian columns across the 

 steppes and deserts of Central Asia to the Khivan oasis, one 

 month wearily plodding through deep snow, the next sinking 

 down in the burning sand, and saved from the most terrible of 

 disasters by the timely discovery of a well ; and, lastly, of the 

 great struggle nearer home, the last echoes of which have hardly 

 yet passed away, when the wave of German conquest, rolling 

 over the Vosges and the Moselle, swept over the various pro- 

 vinces of France. The influence of the earth's crust on war may 

 be regarded as twofold : first, that which it exerts on the general 

 conduct of a campaign ; and, second, that which it exerts on the 

 disijosition and movement of troops on the field of battle. Mili- 

 tary geography treats of the one, military topography of the 

 other ; and it is well to keep this broad distinction in view, for, 

 as with strategy and tactics, they stand in such close relation to 

 each other that it is not always easy to say where geography ends 

 and topography begins. Of special importance in the first case 

 are great inequalities or obstacles that confine or obstruct the 

 movement of large bodies of troops, and those features that 

 retard or accelerate their march. The climate of the theatre of 

 war must always have an important influenceon military operations, 

 and should be the subject of careful study. Our own experience in 

 the Crimea shows how much suffering may be caused by want of 

 forethought in this respect. General Verevkin's remarkable march 

 of more than a thousand miles, from Orenburg to Khiva, with the 

 thermometer ranging from 24° below zero to loo°, without the loss 

 of a man, shows what may be accomplished with due prepara- 

 tion. Nor should the geological structiure of a country be over- 



