ON THE OEiaiN OF THE PLANETARY SYSTEM. 143 



known, and like them are explained on the hypothesis ; 

 and particularly if survivals of the processes, assumed 

 to have taken place in the formation of the heavenly 

 bodies, can be proved to exist in the present. 



Such direct confirmations of various kinds have, in 

 fact, been formed for the view we are about to discuss, 

 and have materially increased its probability. 



Partly this fact, and partly the fact that the 

 hypothesis in question has recently been mentioned in 

 popular and scientific books, in connection with philo- 

 sophical, ethical, and theological questions, have em- 

 boldened me to speak of it here. I intend not so 

 much to tell you anything substantially new in refer- 

 ence to it, as to endeavour to give, as connectedly as 

 possible, the reasons which have led to, and have 

 confirmed it. 



These apologies which I must premise, only apply 

 to the fact that I treat a theme of this kind as a popular 

 lecture. Science is not only entitled, but is indeed 

 beholden, to make such an investigation. For her it is a 

 definite and important question the question, namely, 

 as to the existence of limits to the validity of the laws 

 of nature, which rule all that now surrounds us ; the 

 question whether they have always held in the past, 

 and whether they will always hold in the future ; or 

 whether, on the supposition of an everlasting unifor- 

 mity of natural laws, our conclusions from present 



