MOZLEY ON EVOLUTION. 769 



trine of the correlation of heat and motion, this doctrine had not 

 become current ; and no conception, even, had arisen of the more 

 general doctrine of the correlation and equivalence of the physical 

 forces at large. Still more recent was the rise and establishment of 

 the associated abstract doctrine commonly known as the " conserva- 

 tion of energy." Further, Yon Baer's discovery, that the changes un- 

 dergone during development of each organic body are always from the 

 general to the special, was not enunciated till some eight years after 

 the time at which Mr. Mozley was a pupil of my father, and was not 

 heard of in England until twenty years after. Now, since these three 

 doctrines are indispensable elements of the general theory of evolution 

 (the last of them being that which set up in me the course of thought 

 leading to it), it is manifest that not even a rude conception of such a 

 theory could have been framed at the date referred to in Mr. Mozley's 

 account. Even apart from this, one who compared my successive 

 writings would find clear proof that their cardinal ideas could have 

 had no such origin as Mr. Mozley's account seems to imply. In the 

 earliest of them " Letters on the Proper Sphere of Government " 

 published in 1842 and republished as a pamphlet in 1844, the only 

 point of community with the general doctrine of evolution is a belief 

 in the modifiability of human nature through adaptation to conditions 

 (which I held as a corollary from the theory of Lamarck) and a con- 

 sequent belief in human progression. In the second and more impor- 

 tant one, " Social Statics," published in 1850, the same general ideas 

 are to be seen, worked out more elaborately in their ethical and polit- 

 ical consequences. Only in an essay published in 1852 would the in- 

 quirer note for the first time a passing reference to the increase of 

 heterogeneity as a trait of development, and a first recognition of this 

 trait as seen in other orders of phenomena than those displayed by 

 individual organisms. Onward through essays published in several 

 following years, he would observe further extensions in the alleged 

 range of this law ; until, in 1855, in the " Principles' of Psychology," 

 it begins to take an important position, joined with the additional law 

 of integration, afterward to be similarly extended. Not until 1857, in 

 two essays then published, would he find a statement, relatively crude 

 in form, of the law of evolution, set forth as holding throughout all 

 orders of .phenomena, and joined with it the statement of certain uni- 

 versal physical principles which necessitate its universality. And only 

 in 1861 would he come to an expression of the law approximating 

 in definitenes^ to that final one reached in 1867. All which facts 

 the scientific reader who took the trouble to investigate would see 

 are conclusive against the implication contained in Mr. Mozley's 

 statement ; since, were this implication true, my early writings would 

 have contained traces of the specific doctrine set forth in the later 

 ones. But, as I have said, even a reader of my books can not be 

 trusted to recall a^nd consider these facts, but will certainly, in many 



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