Principles of Molecular Physics. 213 



the discovery made by Encke, that the comet which bears his 

 name affords decisive evidence of the existence of a resisting me- 

 dium in the fields of space, is really no discovery at all. In the 

 first place, the attraction of unknown bodies would in all proba- 

 bility produce effects not recognized in the disturbed motions of 

 Encke's comet — for example, would alter the position of the 

 plane of the orbit. In the second place, Professor Bayma's me- 

 chanics is at fault ; for though the direct tendency of the resist- 

 ance of the supposed medium is to diminish the orbital velocity, 

 a resulting effect is that the orbit is contracted, and the return 

 of the comet to its perihelion expedited. This is Encke' s view 

 of the matter, and it has hitherto met with general acceptance. 

 The words that issue from the filmy trumpet of this unwearied 

 celestial traveller on each successive return have, then, quite a 

 different meaning from those attributed to them by our author, 

 and proclaim the insufficiency of the foundation on which his doc- 

 trine of an attractive sethcr has been erected. 



As to Professor Bayma's comments on the objections urged 

 against this doctrine, I think it must be admitted by the candid 

 reader that the evidence in favour of my view of the constitution 

 of a primitive molecule has been in no degree impaired by his 

 criticisms. His idea that "no possible production of heat and 

 electric currents affords a sufficient ground for assuming a re- 

 duction of resistance and retardation " is altogether fallacious ; 

 for if the impinging atoms of the aether of space take effect 

 directly upon dense electric or sethereal atmospheres enveloping 

 the atoms of gross matter, they may give rise to waves and cur- 

 rents in those atmospheres, propagated thence to other molecular 

 atmospheres, and the energy conveyed by them eventually ra- 

 diated in waves of heat through the interstitial aether and into 

 free space from all sides of the atoms, and with no less intensity 

 from the further sides than from those in advance. A similar 

 principle to this is .admitted in the theory of overshot water- 

 wheels, when it is assumed that the mechanical effect due to the 

 water received into the cell is lost — not communicated to the 

 wheels — being expended primarily in imparting agitations on 

 waves and currents to the water already in the cell, and eventu- 

 ally passing off in the form of heat. The state of the case then 

 is this : the resistance of an sethereal medium in space will 

 not of necessity retard the motions of the planets, if their atoms 

 be surrounded by dense sethereal atmospheres, as I have been 

 led to conceive them to be, on quite different grounds. 



We come now to consider the answer given to my objection 

 to Professor Bayma's doctrine of an attractive medium, viz. that 

 it really involved the operation of an energetic resistance. I 

 freely admit the sufficiency of his answer, if it follows from his 



