i'KKSlDKN'IIAl. AODRKSS — SliCTlON F. I 29 



in character and may be replaced and measured by quantities 

 that stand for weight. The measurable weight serves us, as a 

 certain, convenient, and communicable index, in mechanical re- 

 searches, just as the thermometer in thermal researches is an 

 exacter substitute for our perceptions of heat."^^ 



Herein, then, lie the origin and significance of scientific 

 units and standards of measurement. As is well known, these 

 took their particular form, in the first instance, from facts of 

 habitual experience — the foot, the forearm, the heart-beat, the 

 bow-shot, the day's journey, etc. But the philosophical signifi- 

 cance cif this lies in the truth that only in our sense-impressions 

 have we direct experience of reality — the reality which science 

 aims at interpreting — and that scientific concepts therefore are 

 and must be to the end transcripts of sense-impression. In 

 pursuance of its effort to> interpret reality in the most concise 

 and comprehensive terms, science advances to ever-wider 

 generalizations of experience and the statement of laws of co-exis- 

 tence and sequence in more and more general formulae, until the 

 symbols it uses seem far away from, and to have little reference 

 to, the experiences from which they took their rise. By means 

 of such symbols or conceptual constructions it is able to form 

 a working thought-model of the universe by which to express, 

 as simply and completely as possible, the conditions of experience. 

 But its concepts remain descriptive formulae for phenomenal 

 occurrences or changes, i.e., ifor the order and connexion of our 

 sense-perceptions. 



Accordingly, the road of advance — the way to union of the 

 philosophical and the scientific standpoints — lies in the further 

 analysis of sense-impressions, or, more generally, further elucida- 

 tion of the nature of immediate experience, and the more precise 

 and systematic derivation from these of the conceptions by which 

 it is sought to explain experience. The realization of this is to- 

 day common standing-ground to the experiential philosophers 

 and the philosophical scientists. It is the explicit attitude of the 

 philosophers whose conception of philosophical method I have 

 cited ; and it finds equal expression in the insistence on the part 

 of scientists when they incjuire into the foundations of science, 

 of the need of justifying scientific concepts by derivation from 

 sense-impression, and in their tentative suggestions in this direc- 

 tion. The chief example is Mach's Analysis of the Seusatwns, 

 with its concluding chapter on the influence of this investiga- 

 tion on the mode of conceiving physics. But there are also sug- 

 gestions in Poincare's Science and Hypothesis, in Ostwald's 

 Natural Philosophy, and in Bertrand Russell's Our Khok:- 

 ledge of the External World. Russell shows how some of the 

 main conceptions of science, such as the indestructibility of matter 

 or things, and a single time and space, might be stated in terms 

 of sense-data. He defines a thing as a certain series of aspects 

 or sensible appearances related to one another by continuity and 



^^ Science of Mechanics, pp. 84-5. 



