PHYSICS: J. L ARMOR 
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have been recently current ultimately demand and perhaps prefer the latter 
course; and such modes of expression can apparently be elaborated so as to 
include most of optics, though perhaps in an artificial and unfruitful manner, 
if we replace the Newtonian scalar corpuscles of light by projected vector 
elements of fields of potential (not however conserved in value) from which 
forces would be analytically derivable. Mr. Page's work has improved very 
remarkably such a scheme of projected influence by showing that, provided 
c-relativity is postulated for space and time, it is elements of longitudinal * 
electric force that may be regarded as projected from the sources, and are more- 
over conserved after the manner of quanta as they travel onward. 
There is no absolute criterion to decide between the two ideals. The first 
order of ideas has proved itself as the foundation on which the interlaced fabric 
of electric and optical science has been actually constructed: the other seems to 
offer as yet only somewhat ingenuous and disjointed though significant expres- 
sion for certain striking features of recent discovery which the former has not 
yet succeeded in assimilating, and seems to require us to obliterate the course 
of evolution of the science or perhaps to retain it as a mere historical survival. 
All these modes of restatement of departments of physical science in more ex- 
pressly relative terms may be comprehended as partial analytic developments 
of the far wider principle of the purely relational character of our external 
knowledge, which was advanced and systematically fortified with great abstract 
force in the general metaphysical domain by Bishop Berkeley; a principle by 
means of which he passed on to examine the criterion of real objective exist- 
ence, and one which was well understood in its present aspect by his friends 
in Yale College nearly two centuries ago. 
Thus in these matters we are hardly concerned with refuting any theory, for 
all are relative: it is fruitless to traverse any proposition, unless we take into 
account the definitions and context in which it subsists. The question is, 
as to which scheme of formulation gives as a whole the closest and most ex- 
pressive representation of the complex of natural knowledge, and affords the 
most promising clue to its future elaboration and extension. But a choice 
does not by any means preclude development along other promising but pro- 
visional lines for which an interpretation has yet to be found. A main merit 
of Mr. Page's powerful papers, especially that of 1914, the feature which may 
be said to constitute them into a theory, is to my mind that they translate the 
usual so-called classical electrodynamic theory into the order of ideas, formula- 
tion under relativity of the c type being an essential feature, that describes 
physical action in terms of projected entities (which might perhaps even be 
quanta) of various kinds, effecting this translation in more intuitive and funda- 
mental terms than had previously been attained to; and also that by their 
conciseness and geometrical directness they facilitate that comparison and 
contrast with the alternative order of ideas which is the essential matter. 
1 These Proceedings, 4, 1918, (47-46); Physic. Rev., Ithaca, (Ser. 2), 11, 1918, (376-400). 
