Sepiembee 21, 1900.] 



SCIENCE. 



425 



that are going on in it ; these vibrations 

 being in their normal state characteristic 

 of its dynamical constitution, and in their 

 deviations from the normal giving indi- 

 cations of the velocity of its movement 

 and the physical state of its environment. 

 Maxwell long ago laid emphasis on the fact 

 that a physical atomic theory is not com- 

 petent even to contemplate the vast mass 

 of potentialities and coiTelations of the 

 past and the future, that biological theory 

 has to consider as latent in a single organic 

 germ containing at most only a few million 

 molecules. On our present view we can 

 accept his position that the properties of 

 such a body cannot be those of a ' purely 

 material system,' provided, however, we 

 restrict this phrase to apply to physical 

 properties as here defined. But an exhaust- 

 ive discovery of the intimate nature of the 

 atom is beyond the scope of physics ; ques- 

 tions as to whether it must not necessarily 

 involve in itself some image of the com- 

 plexity of the organic structures of which 

 it can form a correlated part must remain 

 a subject of speculation outside the domain 

 of that science. It might be held that 

 this conception of discrete atoms and con- 

 tinuous tether really stands, like those of 

 space and time, in intimate relation with 

 our modes of mental apprehension, into 

 which any consistent picture of the external 

 world must of necessity be fitted. In any 

 case it would involve abandonment of all 

 the successful traditions of our subject if 

 we ceased to hold that our analysis can be 

 formulated in a consistent and complete 

 manner, so far as it goes, without being 

 necessarily an exhaustive account of phe- 

 nomena that are beyond our range of ex- 

 periment. Such phenomena may be more 

 closely defined as those connected with the 

 processes of intimate combination of the 

 molecules : they include the activities of 

 organic beings which all seem to depend on 

 change of molecular structure. 



If, then, we have so small a hold on the 

 intimate nature of matter, it will appear 

 all the more striking that physicists have 

 been able precisely to divine the mode of 

 operation of the intangible sether, and to- 

 some extent explore in it the fields of phys- 

 ical influence of the molecules. On con- 

 sideration we recognize that this knowledge 

 of fundamental physical interaction has 

 been reached by a comparative process. 

 The mechanism of the propagation of light 

 could never have been studied in the free 

 sether of space alone. It was possible, 

 however, to determine the way in which 

 the characteristics of optical propagation 

 are modified, but not wholly transformed, 

 when it takes place in a transparent ma- 

 terial body instead of empty space. The 

 change in fact arises on account of the 

 sether being entangled with the network of 

 material molecules ; but inasmuch as the 

 length of a single wave of radiation covers 

 thousands of these molecules the wave- 

 motion still remains uniform and does not 

 lose its general type. A wider variation of 

 the experimental conditions has been pro- 

 vided for our examination in the case of 

 those substances in which the phenomenon 

 of double refraction pointed to a change 

 of the sethereal properties which varied in 

 different directions ; and minute study of 

 this modification has proved sufiBcient to 

 guide to a consistent appreciation of the 

 nature of this change, and therefore of the 

 mode of ^ethereal propagation that is thus 

 altered. In the same way, it was the 

 study and development of the manner in 

 which the laws of electric phenomena in 

 material bodies had been unraveled by 

 Ampere and Faraday, that guided Faraday 

 himself and Maxwell — who were impressed 

 with the view that the sether was at the 

 bottom of it all — in their progress towards 

 an application of similar laws to sether 

 devoid of matter, such as would complete 

 a scheme of continuous action by consist- 



