Chase.l -^'4 [April 21, 



referred in foregoing notes, should be thoroughly investigated before 

 forming any conclusive opinion respecting Delaunay's hj^pothesis. Ninth- 

 ly, even after such investigation, the remembrance of other possible un- 

 known influences should prevent anything like dogmatical assertion. 



223. The^'Ifs'' of Elasticity. 



I shall not shrink from any criticism such as is implied in the following 

 "retort courteous" : If there is a universal aethereal medium; if it is 

 endowed with an elasticity somewhat like that of gases ; if its velocity of 

 wave-propagation can be expressed by the ordinary formula of relation 

 between elasticity and density ; if the laws of hannonic vibration in elastic 

 media, which have been mathematically deduced, are correct ; if the 

 aethereal vis viva can be shared with chemical atoms and cosmical masses ; 

 if nebular "subsidence" has been governed by the laws of gravitation ; 

 if all kinds of energy are simple functions of mass and velocity, and "if 

 all the mathematical conclusions which it seems reasonable to draw from" 

 these hypotheses are correct, the general postulate that "all phj^sical 

 phenomena are due to an Omnipresent Power, acting in ways which may 

 be represented by harmonic or cyclical undulations in an elastic medium " 

 may be accepted as a good working hypothesis. 



224. Acceptance of the Issue. 



"These provisos cover the whole ground, as fully .is I could wish. I have 

 never claimed, nor have I believed, that any scientific thesis can be freed 

 from the limitations which are involved in its fundamental assumptions. 

 "While I fully believe in the impossibility of anything acting except where 

 it is, in the existence of a universal elastic medium which is governed by 

 radiodynamic and harmonic laws, and in the uniformity of physical force, 

 I am well aware that they are incapable of mathematical demonstration 

 and I have repeatedly acknowledged that the nebular and sethereal 

 hypotheses have no scientific value beyond such helpful coordination ot 

 phenomena as they may furnish. The tidal "ifs " are mere assumptions, 

 adduced in order to account for an apparent retardation which is altogether 

 problematical and which, if it should prove to be real, may be followed 

 by an equivalent acceleration ; the elastic " ifs " are all intrinsically proba 

 bio, and instead of having been assumed for a special purpose they repre- 

 sent simple and natural generalizations from a wide range of independent 

 physical phenomena. The tidal ifs are like Bacon's "barren virgins ;" 

 the elastic ifs have already led to the discovery of a vast number of natural 

 harmonies and the field for further like discovery widens so rapidly that 

 every physical atom seems to contribute its individual melody, to the ever- 

 resounding and ever-changing choral strains which constitute the music 

 of the spheres. Although centripetal and centrifugal activities may be 

 expressed by identical formuliT?, it is diflicult, if not impossible, to form 

 any definite conception of attracting pulls. Elastic thrusts are exemplified 

 by every breath that we draw, every object that we see, every sound that 



