434 



SCIENCE. 



[N. S. Vol. XII. No. 299. 



ity of an ambitious philosophy, completely 

 unresolved by any theory ' : not many 

 years afterwards the mystery was solved by 

 Fresnel. 



This process of removing the intellectual 

 scaffolding by which our knowledge is 

 reached, and preserving only the final 

 formulae which express the correlations 

 of the directly observable things, may 

 moreover readily be pushed too far. It 

 asserts the conception that the universe 

 is like an enclosed clock that it wound 

 up to go, and that accordingly we can ob- 

 serve that it is going, and can see some 

 of its more superficial movements, but not 

 much of them ; that thus, by patient obser- 

 vation and use of analogy, we can compile, 

 in merely tabular form, information as to 

 the manner in which it works and is likely 

 to go on working, at any rate for some time 

 to come ; but that any attempt to probe 

 the underlying connection is illusory or il- 

 legitimate. As a theoretical precept this 

 is admirable. It minimizes the danger of 

 our ignoring or forgetting the limitations of 

 human faculty, which can only utilize the 

 imperfect representations that the external 

 world impresses on our senses. On the 

 other hand such a reminder has rarely been 

 required by the master minds of modern 

 science, from Descartes and N"ewton on- 

 wards, whatever their theories may have 

 been. Its danger as a dogma lies in its ap- 

 plication. Who is to decide without risk 

 of error, what is essential fact and what is 

 intellectual scaffolding? To which class 

 does the atomic theory of matter belong? 

 That is, indeed, one of the intangible things 

 which it is suggested may be thrown over- 

 board, in sorting out and classifying our 

 scientific possessions. Is the mental idea 

 or image, which suggests, and alone can 

 suggest, the experiment that adds to our 

 concrete knowledge, less real than the bare 

 phenomenal uniformity which it has re- 

 vealed ? Is it not, perhaps, more real in 



that the uniformities might not have been 

 there in the absence of the mind to perceive 

 them? 



No time is now left for review of the 

 methods of molecular dynamics. Here our 

 knowledge is entirely confined to steady 

 states of the molecular system : it is purely 

 statical. In ordinary statics and the dy- 

 namics of undisturbed steady motions, the 

 form of the energy function is the suf- 

 ficient basis of the whole subject. This 

 method is extended to thermo-dynamics by 

 making use of the mechanically available 

 energy of Rankine and Kelvin, which is a 

 function of the bodily configuration and 

 chemical constitution and temperature of 

 the system, whose value cannot under any 

 circumstances spontaneously increase, while 

 it will diminish in any operation which 

 is not reversible. In the statics of sys- 

 tems in equilibrium or in steady motion, this 

 method of energy is a particular case of 

 the method of Action ; but in its extension 

 to thermal statics it is made to include 

 chemical as well as configurational changes, 

 and a new point appears to arise. Whether 

 we do or do not take it to be possible to 

 trace the application of the principle of 

 Action throughout the process of chemical 

 combination of two molecules, we certainly 

 here postulate that the static case of that 

 principle, which applies to steady systems, 

 can be extended across chemical combina- 

 tions. The question is suggested whether 

 extension would also be valid to trans- 

 formations which involve vital processes. 

 This seems to be still considered an open 

 question by the best authorities. If it be 

 decided in the negative a distinction is in- 

 volved between vital and merely chemical 

 processes. 



It is now taken as established that vital 

 activity cannot create energy, at any rate 

 in the long run which is all that can from 

 the nature of the case to be tested. It 

 seems not unreasonable to follow the anal- 



