132 DARWINIANA. 



has reached high tide, and is now the pervading, the 

 fully-established system. There was an intervening 

 time during which most physicists held their opinions 

 in suspense. 



The adoj)tion of the undulatory theory of light 

 called for the extension of the same theory to heat, 

 and this promptly suggested the hypothesis of a 

 correlation, material connection, and transmutability 

 of heat, light, electricity, magnetism, etc. ; which hy- 

 pothesis the physicists held in absolute suspense until 

 very lately, but are now generally adopting. If not 

 already established as a system, it promises soon to 

 become so. At least, it is generally received as a 

 tenable and probably true hypothesis. 



Parallel to this, however less cogent the reasons, 

 Darwin and others, having shown it likely that some 

 varieties of plants or animals have diverged in time 

 into cognate species, or into forms as different as spe- 

 cies, are led to infer that all species of a genus may 

 have thus diverged from a common stock, and thence 

 to suppose a higher community of origin in ages still 

 farther back, and so on. Following the safe example 

 of the physicists, and acknowledging the fact of the 

 diversification of a once homogeneous species into 

 varieties, we may receive the theory of the evolution 

 of these into species, even while for the present we 

 hold the hypothesis of a further evolution in cool 

 susj)ense or in grave suspicion. In respect to very 

 many questions a wise man's mind rests long in a state 

 neither of belief nor of unbelief. But your intellect- 

 ually short-sighted people are apt to be preternaturally 

 clear-sighted, and to find their way very plain to posi- 



