October 24, 1913] 



SCIENCE 



579 



a remarkable example of the union of two 

 sets of motives. The whole experience of 

 modern industrial art gave rise to the in- 

 duction that perpetual motion is in all 

 forms impossible, that all sorts of energy 

 must be paid for if you mean to use them, 

 and that the expenditure of any form of 

 energy takes place in one direction only, 

 or, in other words, that energy will not, so 

 to speak, run up hill without special costs 

 due to the process whereby it is set running 

 up hill. These were practical inductions, 

 forced upon the users of machines by con- 

 siderations of need, economy and expense. 

 The steam engine especially taught lessons 

 of this sort, and led Carnot to his famous 

 ' ' Reflections on the Motor Power of Heat. ' ' 

 Here lay concealed one side of the coming 

 energy theory. In England a similar 

 union of technological and physical re- 

 search also led to the threshold of the final 

 generalization. But an important part of 

 the theory was due to quite another sort of 

 man, viz., to a medical man, and one who 

 was in spirit a good deal disposed to large 

 syntheses of a type similar to those of the 

 former Naturphilosophie. In the early 

 forties, Mayer had his attention called, 

 while he was physician in charge of a 

 ship's company in the tropics, to the fact 

 that the venous and the arterial blood of 

 his patients were not so different from one 

 another in color as they were in a colder 

 climate. This single fact aroused a long 

 series of reflections upon the process of 

 oxidation in its relation to the production 

 of heat in the organism, and then upon the 

 relation of chemical and organic processes 

 in general, and then upon the relations of 

 both to physical processes. Before Mayer 

 returned to Europe, he had his mind full of 

 an universal theory of the relations of the 

 natural energies, organic as well as inor- 

 ganic. The theory had the advantage over 

 the Schellingian type of theory that it could 



be brought into exact relations to experi- 

 ence, and so tested. But in its origin it was 

 a theory of a philosophical type such as the 

 older Naturphilosophie might have used 

 had it been acquainted with what the sci- 

 ence of 1840 knew. 



It was the union of philosophical inter- 

 ests and industrial needs that thus gave 

 birth to the modern doctrine of energy. 

 The moral seems to be that one very good 

 foundation for important scientific gen- 

 eralizations lies in bringing into close rela- 

 tions widely philosophical and intensely 

 and imperiously practical human interests. 

 I think that, as the foregoing historical 

 examples show, medicine itself has more 

 than once greatly profited by just such 

 an union. The industrial and the medical 

 arts, if too much oppressed by the mere 

 desire to accommodate themselves to the 

 momentary needs of individual men, tend, 

 when left to themselves, towards a shallow 

 and unprogressive empiricism. Philos- 

 ophy, by itself, tends, when applied to the 

 subject matter of such arts, to fruitlessly 

 vague dreams. But the union of the in- 

 dustrial or the strictly practical and the 

 philosophical spirit tends to produce men 

 like Virchow, or doctrines like the modern 

 doctrine of energy. Hence I myself heart- 

 ily welcome the introduction of technolog- 

 ical enterprises into modern universities; 

 and I also believe that the useful arts are 

 all the better off for being troubled occa- 

 sionally, by the neighborhood of philos- 

 ophy. Philosophy, on the one hand, and 

 the useful arts, on the other, are too often 

 somewhat like the pine and the palm tree 

 of Heine's well-known lyric. They are far 

 apart; but they sometimes long for each 

 other. It is a pity to keep them in such 

 isolation. 



IV 



But now, finally, what follows from the 

 foregoing historical sketch for our under- 



