THE CHAIN OF LIFE. 



CHAPTER I. 



PRELIMINARY CONSIDERATIONS AS TO THE EXTENT AND 

 SOURCES OF OUR KNOWLEDGE. 



IT is of the nature of true science to take nothing on trust or 

 on authority. Every fact must be established by accurate 

 observation, experiment, or calculation. Every law and prin- 

 ciple must rest on inductive argument. The apostolic motto, 

 " Prove all things, hold fast that which is good," is thoroughly 

 scientific. It is true that the mere reader of popular science 

 must often be content to take that on testimony which he 

 cannot personally verify ; but it is desirable that even the most 

 cursory reader should fully comprehend the modes in which 

 facts are ascertained and the reasons on which conclusions are 

 based. Failing this, he loses all the benefit of his reading in 

 so far as training is concerned, and cannot have full assurance 

 of that which he believes. When, therefore, we speak of life- 

 epochs, or of links in a chain of living beings, the question is 

 at once raised — What evidence have we of the succession of 

 such epochs? This question, with some accessory points, 

 must engage our attention in the present chapter. 



B 



