SOME REMARKS, &c. 39 



ciples a finite intelligence might be conceived to exist by which 

 all the phenomena of the universe would be fully comprehended, 

 does not (whatever may be thought of its validity) appear to 

 apply to the views which I have been led to entertain. For 

 these views essentially depend on the conception of what may 

 be called a hierarchy of causes, to which we have no reason for 

 assigning any finite limit. Of this series of principles of causa- 

 tion, ordinary mechanical force is the first term. 



3. With respect to the first point, namely, the impossibility 

 of explaining all phenomena mechanically, it may be remarked, 

 that we are met, in the attempt to discuss it, by the difficulty 

 which always attends the establishment of a negative proposition. 

 It is clear that as in the present state of our knowledge we are far 

 from being able to enumerate and classify the phenomena which 

 are or which might be produced by the combined agency of con- 

 ceivable mechanical forces, we are not in a position to decide 

 a priori that any given phenomenon might not be thus produced. 

 Non constatj but that the impossibility we find in the attempt to 

 explain the causes of its existence may have no higher origin 

 than the imperfect command which we have as yet obtained of 

 the principles of mechanical causation. We meet, it may be 

 said, with a multitude of ordinary dynamical problems which 

 have as yet received no adequate solution why then should we 

 have recourse to new kinds of causes, while we have not as yet 

 exhausted the resources, if the expression may thus be used, of 

 those which we already recognise? To this enquiry no con- 

 clusive answer can be given, but the following considerations 

 will I think naturally suggest themselves. 



4. In the first place, no even moderately successful attempt 

 has, I think, yet been made to explain any chemical phenomenon 

 on mechanical principles. It is quite true that we are unable, 

 to take a particular instance, fully to comprehend the mechanical 

 constitution of the luminiferous ether ; the determinations which 

 have as yet been attempted of the law of attraction between its 

 molecules cannot, I apprehend, be accepted as any thing more 

 than hypothetical or provisional results, and there are other 

 points involved in yet greater obscurity. Nevertheless the un- 

 dulatory theory of light has, as we all know, given consistent 

 and satisfactory explanations of a great variety of phenomena. 



