CONCEPTS OF PHYSICAL SCIENCE. 61 



panying it anomalous dispersion. For these and numerous other 

 phenomena no adequate theory is possible which does not have its 

 foundation upon some assumed conception as to the constitution of 

 matter. 



The development of the modern idea of the ether forms one of the 

 most interesting chapters in the history of physics. We find at first a 

 tendency to assume a number of distinct media corresponding to the 

 various effects (visual, chemical, thermal, phosphorescent, etc.) of light 

 waves, and later the growth of the conception of a single medium, the 

 luminiferous ether. 



In the development of electricity and magnetism, meantime, the 

 assumption of media was found to be an intellectual necessity without 

 which no definite philosophy of the phenomena was possible. At first 

 there was the same tendency to a multiplicity of media — there were 

 the positive and negative electric fluids, the magnetic fluid, etc. Then 

 there grew up in the fertile mind of Faraday that wonderful fabric 

 of the scientific imagination, the electric field; the conception upon 

 which all later attempts to form an idea of a thinkable mechanism of 

 electric and magnetic action have been established. 



It is the object of science, as has been pointed out by Ostwald, to 

 reduce the number of hypotheses, and the highest development would be 

 that in which a single hypothesis served to elucidate the relations of the 

 entire universe. Maxwell's discovery that the whole theory of optics is 

 capable of expression in terms identical with those found most con- 

 venient and suitable in electricity, in a word that optics may be treated 

 simply as a branch of electromagnetics, was the first great step towards 

 such a simplification of our fundamental conceptions. This was fol- 

 lowed by Hertz's experimental demonstration of the existence of arti- 

 ficially produced electromagnetic waves in every respect identical with 

 light waves, an achievement which served to establish upon a sure foun- 

 dation the conception of a single medium. The idea of one universal 

 medium as the mechanical basis for all physical phenomena was not 

 altogether new to the theoretical physicist but the unification of optics 

 and electricity did much to strengthen this conception. 



The question of the ultimate structure of matter, as has already 

 been pointed out, is also speculative in the sense that the mechanism 

 upon which its properties are based is out of the range of direct 

 observation. For the older chemistry and the older molecular physics 

 the assumption of an absolutely simple atom and of molecules com- 

 posed of comparatively simple groupings of such atoms sufficed. Phys- 

 ical chemistry and that new phase of molecular physics which has 

 been termed the physics of the ion demand the breaking up of the 

 atom into still smaller parts and the clothing of these with an electric 

 charge. The extreme step in this direction is the suggestion of Larmor 

 that the electron is a ' disembodied charge ' of negative electricity. 



Since, however, in the last analysis, the only conception having a 



