PREFACE. Vll 



years, I find that many of them would need to be rewritten 

 to meet the demands of fresh discovery or more exact know- 

 ledge ; while the questions involved in others have been so 

 largely handled in modern controversy, that my treatment 

 of them would have little other novelty than perhaps a closer 

 concentration of the argument upon the conclusion sought 

 for. Such method indeed, explicitly followed, has especial 

 value in questions of the kind here alluded to. Strong or 

 crucial proofs are enfeebled by contact with weaker ones, and 

 an argument may be prolonged until it loses all its pith and 

 purport. 



Judging, then, that the larger part of these papers could 

 not be published in their present shape, and seeing that 

 needful changes could not be incorporated without rewriting 

 the whole, which at the age of eighty-five would have been an 

 impossible task, I have thought it best to summarise in a 

 more abridged form what may seem worth retaining of their 

 contents, with such additions as are suggested by the progress 

 of recent research. Such summary indeed I cannot feel to 

 be an easy one. Discovery has been largely at work of late 

 in every branch of human knowledge, and even these con- 

 nexions and correlations in the physical sciences, now so 

 extensively developed, while concentrating physical pheno- 

 mena, whether of living or lifeless matter, round certain 

 foci, have virtually extended the field of research by bringing 

 into view not only new classes of facts, but also those pro- 

 found laws of force and motion upon which these inter- 

 relations depend. The horizon of our knowledge continually, 

 though unequally, expands obscure in its boundary on every 

 side, and ultimately defined by limits impassable to human 

 reason. One man by genius or happy accident may press 

 more closely than another towards, this horizon ; but the 

 ultimate limit is the same to all, involving those mysteries 

 of Matter, Force, and Creative or Governmental Power, to 

 which all other problems are subordinate. 



