﻿Principles of Molecular Physics. 357 



sultant attractive or repulsive according as the atoms acted on 

 are supposed to be placed beyond or within the limits of their 

 molecular distance of equilibrium. This is the only inference 

 that can be drawn legitimately from the impenetrability of mo- 

 lecules. 



I might dispense with all remarks on what the writer adds 

 about a conception which he himself as yet hesitates to adopt. 

 The idea however is calculated by its novelty and brilliancy 

 to fascinate a mind devoted to physical speculation, and de- 

 serves a short notice. The author says : 



" But another conception may be formed of the mode of opera- 

 tion of an atom of gross matter, which involves no other supposition 

 than that it acts equally outwards in all directions from a centre, 

 and takes no account of its geometrical extent. This is that the 

 effective attraction of the atom for the (Ether of space is due to the ex- 

 istence of a repulsion less than would be exerted by the one or more 

 atoms of (Ether that would naturally occupy its place. The result 

 would be the condensation of an atmosphere of aether around the 

 atom, without the exertion of any direct attractive foice, or of any 

 additional force of resistance. We may conceive the molecular at- 

 mosphere of electric aether to originate in a similar way ; but as the 

 opportunity of examining and testing this idea sufficiently has not 

 yet been obtained, I shall continue to regard the electric aether as 

 directly attracted by the atom of gross matter, and that the antago- 

 nistic force of resistance is furnished by the repulsion of the lumini- 

 ferous aether condensed around the atom." 



This conception, however plausible it may be, is exposed to 

 many serious objections, which however I am not ready to treat 

 in this paper, as I must confine myself to the questions already 

 raised. The least that I can say of this new theory is that it is 

 quite unnecessary, and that, no matter how much talent may be 

 spent in building it, it will never be more than an a priori as- 

 sumption; for in the whole multitude and variety of natural 

 facts nothing has yet been found which can serve as a basis for 

 its future demonstration. Professor Norton himself says that 

 the opportunity of examining and testing this idea sufficiently 

 has not yet been obtained : I rather think that the idea has not 

 even begun to be tested, and never will, unless the question be 

 of testing its inadmissibility. For, though there are no facts in 

 nature supporting the hypothesis, there are facts strongly con- 

 tradicting i^ as for instance molecular cohesion and gravitation. 

 Moreover, this new hypothesis would not have for its result "the 

 condensation of an atmosphere of aether around the atom without 

 the exertion of any direct attractive force," as assumed by Pro- 

 fessor Norton. The hypothesis that the atom of gross matter 

 repels less than the aether which would naturally occupy its 



