Notices respecting New Books, 301 



emitted, reflected, refracted, inflected, and warms bodies ; and all 

 sensation is excited, and the limbs of animals are moved nt will, that 

 is, by vibrations of this spirit propagated through the solid fibres of 

 the nerves from the external organs of sense to the brain, and from 

 the brain to the muscles. But these things cannot be expounded in 

 few words ; neither does there exist a sufficient abundance of expe- 

 riments, by which the laws of the action of this spirit can be accu- 

 rately determined and demonstrated." The following is the quotation 

 from the ' Optics' : — " Is not heat conveyed through a vacuum by the 

 vibrations of a much more subtile medium than air ? Is not this me- 

 dium the same by which light is refracted and reflected, and commu- 

 nicates heat to bodies, and is put into fits of easy reflexion and trans- 

 mission ? Do not hot bodies communicate their heat to cold ones by 

 the vibrations of this medium ? And is it not exceedingly more rare 

 and subtile than air, and exceedingly more elastic and active ? And 

 does it not readily pervade all bodies ? And is it not, by its elastic force, 

 expanded through all the heavens ?" Two inferences may clearly 

 be drawn from these views : — first, that according to Newton the 

 forces of nature are resident in a very subtle spirit, or medium, which 

 pervades all other bodies, and is extremely elastic ; that they are, in 

 fact, modes of action of this medium, one of which he particularly 

 specifies, namely, action by vibrations : secondly, that he ascribes no 

 active power, or virtue, to bodies which are distinct from the elastic 

 medium. In another part of the third book (Regula III.), he says 

 expressly, " I by no means affirm that gravity is essential to bodies." 

 Also there is 'no evidence in the above passages, or elsewhere in 

 Newton's writings, that he took account of an atomic constitution 

 of the medium, the very term " elastic," as used in his sense, im- 

 plying that he regarded it as continuous, and acting by pressure just 

 as the air does, only in much greater degree. Now let us turn to 

 Mr. Birks's views. At the same time that he adduces Newton's 

 "prophecy," he appears to do all he can to falsify it. The general 

 view that he takes of matter is that " it consists of monads, or 

 moveable centres of force, unextended, but definite in position." 

 Such monads, which in other places he calls " atoms " and " parti- 

 cles," without expressly ascribing to them extension or inertia, he 

 considers to be the constituents both of the aether, and of visible and 

 tangible bodies. Thus he opposes Newton in two most important 

 particulars : first, in making active force an essential quality of the 

 constituents of visible bodies, whereas Newton in Regula III. allows 

 of no other essential force (vim insitam) in such bodies than the vis 

 inertia ; and again, in making it an essential condition of his physical 

 theory to regard the aether as consisting of monads. 



Again, there is a passage in the Regula III., as remarkable as the 

 two before quoted, which also contains views directly opposed to 

 those of Mr.Birks. Newton says, "The extension, hardness, impene- 

 trability, mobility, and vis inertia of the whole arise from the very 

 same qualities of the parts ; and thence we conclude that all the 

 least parts of all bodies are extended, hard, impenetrable, moveable, 

 and endowed with vis inertia. And this is the foundation of all 



