September 12, 1884. 



SCIENCE. 



235 



ors showed that affinity is definite in action and 

 amount: it has limits, or proceeds per saltum. Ber- 

 thollet contended that affinity is not definite: he 

 proves that it is often controlled by the nature and 

 the masses of the reacting bodies. Dalton, Berzelius, 

 Wollaston, and others held, on the contrary, this 

 force to be definite, and to act per saltum : it is a 

 power which emanates from the atom. Davy, Am- 

 pere, and Berzelius believed affinity to be a conse- 

 quence of electrical action. Avogadro in one way, 

 and Brodie in another, show us affinity exerted by 

 molecules as well as atoms. It is a force which binds 

 together, not only particles of the same substance, 

 but also of heterogeneous substances. From the fact 

 of the actual existence of radicles, and from the phe- 

 nomena of substitution, was developed the notion of 

 position, and that, therefore, affinity varied with the 

 structure of the body as well as with its composition. 

 The differences between the number of atoms which 

 are equal to hydrogen in replacing power have led to 

 the doctrine of valence, which, if it has any influence 

 on theories of affinity, shows that this property of 

 matter has two distinct concepts, — one, its power 

 of attracting a number of atoms ; the other, its 

 power of doing work or evolving energy. These two 

 attributes seem to be in no way related to each other. 

 Mendelejeff and Lothan Meyer have shown, by the 

 facts which are grouped under the title ' periodic 

 law,' that the properties of elements seem to be 

 repeating functions of the atomic weight. Hence 

 affinity is connected in some way with that same 

 property, which is also shown by the differential ac- 

 tion of gravitation on the absolute chemical unit of 

 matter. Finally, Williamson, Kekule, and Michaelis 

 have suggested that combination is brought about 

 and maintained by incessant atomic interchange ; 

 hence, that affinity is fundamentally due to some 

 form of vibration. 



The idea which seemed so simple and natural a one 

 to Hippocrates has grown successively more complex 

 and less sharply defined; and we are compelled to 

 admit that the years have not brought the theory of 

 affinity to a state of active growth. Chemists have 

 more and more turned their attention to details, to 

 accumulating methods of analysis and synthesis, 

 to questions of the constitution of salts, to discus- 

 sions about graphic and structural formulae, and to 

 hypotheses about the number and arrangement of 

 atoms in a molecule; but they have not, until quite 

 recently, made systematic attempts to measure the 

 energies involved in reactions. Why ? The answer 

 can be found mainly in two reasons. First, the word 

 'affinity' is in bad odor. We see how enormously 

 complicated the phenomena of chemical action have 

 become, and we have lost all faith in hypotheses 

 which can be evolved by the mere force of meta- 

 physical introspection. Second, there is a more im- 

 portant reason, arising from what has hitherto been 

 the traditional scope of our science. Chemistry alone 

 of the physical sciences has offered no foothold to 

 mathematics; and yet all her transformations are 

 governed by the numbers which we call ' atomic 

 weights.' What is it which causes chemistry, so pre- 



eminently the analytic science of material things, to 

 be the only one which does not invite the aid of 

 mathematics ? It is because three fundamental con- 

 ceptions underlie physics, while only two serve the 

 needs of the chemist. If a term so much used just 

 now by transcendental geometers may be borrowed, 

 one would say that physics is a science of three 

 dimensions, while chemistry is a science of two di- 

 mensions. In the first, nearly every transformation 

 is followed by its equation of energy; and this in- 

 volves the concepts space, mass, time: while, in the 

 second, an ordinary chemical equation gives us 

 the changes of matter in terms of space and mass 

 only; that is to say, in units of atomic weight and 

 atomic volume. 



Think for a moment what physics would be to-day 

 without those grand generalizations, Newton's theory 

 of gravitation, Young's undulatory theory of light, 

 the dynamic theory of heat, the kinetic theory of 

 gases, the conservation of energy, and Ohm's law in 

 electricity. Every one of these, except the last, is a 

 dynamic hypothesis, and involves velocity — that is, 

 time — as one of its essential parts. In comparison 

 with the above, all ordinary chemical work may be 

 termed the registration of successive static states of 

 matter. The analyst pulls to pieces, the synthetic 

 chemist builds up; each records his work as so many 

 atoms transferred from one condition to another, and 

 he is satisfied to exhibit the body produced quietly 

 resting in the bottom of a beaker, motionless, static. 

 The electrolytic cell tells us the stress of chemism 

 for specified conditions as electromotive force; the 

 splendid work done in thermo-chemistry enables us 

 to know the whole energy involved when A unites 

 with B, or when A B goes through any transforma- 

 tion however intricate, but it does not inform us of 

 the dynamic equation which accompanies them, and 

 which should account for the interval between the 

 static states. 



Whenever we look outside of chemistry, we find that 

 the lines of the great theories along which progress is 

 making are those of dynamic hypotheses. If we go 

 to our biological brethren, we see them too moving 

 with the current; the geologist studies upheavals, 

 denudation, rate of subsidence, glacial action, and all 

 kinds of changes, in reference to their velocity ; the 

 physiologist is actively registering the time element 

 in vital phenomena, through the rate of nervous 

 transmission, the rate of muscular contraction, the 

 duration of optical and auditory impressions, etc. ; 

 even the sociologist is beginning to hint at velocities, 

 as, indeed, we should expect in a student of revolu- 

 tions; and we cannot ignore the fact that all the 

 great living theories of the present contain the time 

 element as an essential part. The speaker could but 

 think the reason that chemistry has evolved no great 

 dynamical theory, that the word 'affinity' has disap- 

 peared from our books, and that we go on accumulat- 

 ing facts in all directions but one, and fail to draw 

 any large generalization which shall include them 

 all, is just because we have made so little use of the 

 fundamental concept, time. To expect to draw a 

 theory of chemical phenomena from the study of 



