CHAP. XII.] AND PERCEPTION. 175 



synchronically ; most of those which are observed succes- 

 sively are frequently observed successively." * But the 

 effects of such repetitions of Sensations, ' associated ' by 

 their occurrence either " precisely at the same instant of 

 time or in the contiguous successive instants," and 

 whether referring to the same object or to different ob- 

 jects, were clearly enunciated nearly a century and a half 

 ago by Hartley in his celebrated ' Doctrine of Associa- 

 tion.'! He then laid down the following important law 

 of Mind : "Any Sensations, A,B,C, dc., by being asso- 

 ciated with one another a sufficient Number of Times, get 

 such a Power over the corresponding Ideas, a, b, c, dc., 

 that any one of the Sensations A, when impressed alone, 

 shall be able to excite in the Mind b, c, dec., the Ideas of 

 the rest" Muscular Motions were also shown by 

 HartleyJ to exhibit a similar tendency to cohere with 

 Sensations and Ideas, and " the whole doctrine of asso- 

 ciation " was comprised by him in a ' theorem ' to that 

 effect, almost precisely similar to what has been re-affirmed 

 and fully illustrated in our own time, by Alexander Bain, 

 as ' The Law of Contiguity.' 



Hartley, moreover, showed that " Simple Ideas will run 

 into complex ones, by means of Association ; " and on this 

 head James Mill says : " Ideas, also, which have been so 

 often conjoined that whenever one exists in the mind the 

 other exists along with it, seem to run into one another, 

 to coalesce, as it were, and out of many to form one idea, 

 which idea, however, in reality complex, appears to be no 

 less simple than any one of those of which it is com- 

 pounded. . . . The word 'gold,' for example, or the word 

 'iron,' appears to express as simple an idea as the word 



* James Mill, loc. cit., p. 55. 



t "Observations on Man." Sixth Edition, 1834, p. 41. 



% Loc. cit., p. 65. 



