IV 



Professors, who had to perform, in addition to their own proper 

 duties, those which are now assigned to lecturers and assistants. It 

 became necessary, therefore, to extend the teaching powers of the 

 College, and it was resolved as a first step to appoint a college tutor 

 to assist the students in their various studies. This office Mr. Jevons 

 was prevailed upon to accept. Few men could have been found so 

 competent to fill it, his fulness of knowledge and versatility of mind 

 qualifying him for the work in a very remarkable degree. " The 

 multiplicity of the London University system," writes one of his 

 colleagues, " had at no time any terrors for him, and I have known 

 very few men so admirably endowed as he was with the continuation 

 of force and elasticity necessary for confronting it." For three years 

 he served the College in this capacity with distinguished ability and 

 success. In 1866 some changes occurred in the personnel of the 

 teaching staff, and Mr, Jevons was elected to a professorship. The 

 chairs of Logic and Political Economy being united, were intrusted to 

 him, and in this new position he found employment entirely adapted 

 to his gifts and tastes. Logic had become his favourite but not 

 exclusive study. Meteorology and the physical sciences had lost much 

 of their hold upon him ; but the theory of economics and problems 

 connected therewith still continued to engage part of his attention. 

 The influences that mainly contributed to mould the form and direct 

 the progress of his logical investigations may here be noticed. 



While residing in Australia he had read with care Mr. Mill's great 

 work on Logic, and the interest then awakened in his mind was 

 revived and strengthened on his return to England by listening to the 

 lectures and reading the works of Professor De Morgan, that prince 

 of teachers, to whom he often and warmly acknowledged his great in- 

 debtedness, as having inspired him with a deep love for logical method, 

 and taught him to acquire those habits of exact thought and reasoning 

 which are a better mental possession than any amount of mere know- 

 ledge. From De Morgan, also, he probably derived his tendency to 

 look at logic on its mathematical side. But the man whose writings 

 more, perhaps, than any other influenced the course of his logical 

 speculations was Professor Boole. With the " Investigations of the 

 Laws of Thought " Jevons first became acquainted in 1860, and from 

 that date, throughout the remainder of his life, the science of logic 

 occupied a prominent place in his studies. The boldness, originality, 

 and beauty of Boole's system captivated him. As a generalisation of 

 reasoning, he regarded it as vastly superior to anything previously 

 known ; but there were some portions of it that seemed to him dark 

 and mysterious, and these he sought to separate from what he con- 

 sidered clear and unassailable. The calculus of and 1, which plays 

 so important a part in Boole's method, Jevons rejected on the ground 

 that it represents other operations than those of common thought. 



