400 FEAGMENTS OF SCIENCE. 



part, pro or con, in reference to the theory of evolu-' 

 tion, I have had the honour of addressing audiences in 

 Liverpool, Belfast, and Birmingham; and in these ad- 

 dresses the theory of evolution, and the connected doc- 

 trine of spontaneous generation, have been more or 

 less touched upon. Let us now examine whether in 

 my references I have departed from the views of Vir- 

 chow or not. 



In the Liverpool discourse, after speaking of the 

 theory of evolution when applied to the primitive con- 

 dition of matter, as belonging to ' the dim twilight of 

 conjecture/ and affirming that ' the certainty of experi- 

 mental enquiry is here shut out/ I sketch the nebular 

 theory as enunciated by Kant and Laplace, and after- 

 wards proceed thus: ' Accepting some such view of the 

 construction of our system as probable, a desire imme- 

 diately arises to connect the present life of our planet 

 with the past. We wish to know something of our re- 

 motest ancestry. On its first detachment from the 

 sun, life, as we understand it, could not have been 

 present on the earth. How, then, did it come there? 

 The thing to be encouraged here is a reverent freedom 

 a freedom preceded by the hard discipline which 

 checks licentiousness in speculation while the thing to 

 be repressed, both in science and out of it, is dogma- 

 tism. And here I am in the hands of the meeting, will- 

 ing to end but ready to go on. I have no right to intrude 

 upon you unasked the unformed notions which are float- 

 ing like clouds, or gathering to more solid consistency 

 in the modern speculative mind.' 



I then notice more especially the basis of the theory. 

 ' Those who hold the doctrine of evolution are ~by no 

 means ignorant of the uncertainty of their data, and 

 they only yield to it a provisional assent. They re- 

 gard the nebular hypothesis as probable; and, in the 



