176 



SCIENCE 



[N. S. Vol. XLIX. No. 1260 



tlie philosophy of science referred to easily 

 leads to the conclusion that the discovery of 

 new facts is of supreme value in science and 

 that one is doing good scientific work when he 

 ■ adds a few facts to our already unwieldy 

 accumulation of Imowledge, whether the facts 

 discovered have any valuable relation to fun- 

 damental principles or not. 



Another school of philosophers contends 

 that the number of explanations which will fit 

 any given set of natural phenomena is in- 

 finite, and that, for this reason, any explana- 

 tion which we use, as for instance, the Coper- 

 niean system or the atomic theory, is purely 

 a product of our imagination and that it is 

 hopeless ever to arrive at a system which 

 shall actually correspond to the realities of 

 the universe. This, if I understand him cor- 

 rectly, was the point of view held by Poincare. 

 It is only a step from this to the conclusion 

 that there is no reality outside of our own 

 minds, for, surely, if we can never attain to a 

 knowledge of realities outside ourselves, for 

 all practical purposes such realities do not 

 exist. 



A more true philosophy of science, as it 

 seems to me, recognizes the intimate con- 

 nection between speculation, hypothesis and 

 theory on the one hand and the accurate study 

 of phenomena on the other. ITeither is com- 

 plete or sufficient alone. Science advances 

 most rapidly by what may be called a " cut- 

 and-try" method. Speculation alone led to 

 the useless dialectics of the school-men. A 

 study of phenomena alone leads to an almost 

 equally barren acciumulation of facts for 

 which we have no earthly use. It is incon- 

 ceivable that chemistry, or indeed, that sci- 

 ence as a whole could have made the progress 

 that it has during the last century if Dalton, 

 or some one else, had not given us the atomic 

 hypothesis as a key for the study of chemical 

 phenomena. 



The subject of valence furnishes a particu- 

 larly good illustration of the methods by 

 which science advances. The positive achieve- 

 ments of the theory are so great that no one 

 can doubt that there is some reality in the 



relations of atoms which corresponds to the 

 theory. At the same time our knowledge is 

 so vague and indefinite at many points that 

 we must consider the theoi"y as still very un- 

 satisfactory and in need of further develop- 

 ment. 



Ernst von Meyer has pointed out with some 

 truth that the tlieory of valence is implied 

 in the Law of Multiple Proportions. A some- 

 what more definite approach was made when 

 Graham demonstrated the polybasic character 

 of phosphoric acid. His results were ex- 

 pressed, however, in the old dualistic for- 

 mulas in which one, two or three molecules of 

 water of hydration in the acid were considered 

 as replaced by one, two or three molecules of a 

 metallic oxide. When Liebig introduced the 

 idea that acids are compounds of hydrogen 

 the notion of polybasic acids became still 

 more definite and the fact that an atom of 

 antimony may replace three atoms of hy- 

 drogen while an atom of potassium replaces 

 only one was given a clear statement. During 

 the same period the discovery of the ehloro- 

 aeetics acids by Dvunas and the development of 

 the theory of types by Gerhardt and others 

 gave greater precision to our knowledge of 

 the replacement of one atom by another and 

 it became evident that in such replacements 

 one atom of oxygen may take the place of 

 two atoms of chlorine. 



Thus far the rudiments of the idea of 

 valence had been developed only on the basis 

 of the replacing power of different atoms. 

 In 1852 Frankland went a step further and 

 introduced the more exact conception of a 

 definite, though variable, combining power 

 for different atoms. Using the atomic weight 

 8 for oxygen he gives the formulas 1^0^, NHg, 

 Nl^, IsTSg; PO3, PH3, PCI3; SbOj, SbHj, 

 SbClj; AsO.,, AsHj, and NO,, ISTH.O, ISTHJ; 

 POg, PHjI, etc., to show that the elements 

 nitrogen, phosphorus, arsenic and antimony 

 combine with either three or five atoms of 

 other elements. He also pointed out that 

 when an atom of tin is combined with two 

 ethyl groups in tin ethyl, Sn(C„H5)2, it will 

 take up only one atom of oxygen, giving the 



