MENTAL OPERATIONS IN RELATION TO TIME. Ill 



active faculty of niind, and one which strikingly illus- 

 trates the diversity of power in different individuals as 

 well as in the same person at different times. I might 

 say much on these phenomena of memory and recol- 

 lection, as bearing on the subject before us ; but they 

 are too numerous and complex to be dealt with as a 

 mere appendage to other enquiry. 



Another remark, however, occurs which cannot 

 well be detached from the general method of enquiry 

 I am sugesting. In writing elsewhere on the pheno- 

 mena of sleep and dreams I have noticed our imper- 

 fect knowledge of these functions, as concerns the 

 changes they presumably undergo at different ages, 

 and under different conditions of life. This remark 

 applies not less to the processes and associations of the 

 waking mind. We go but partially to work in analy- 

 sing the acts of the adult and cultivated intellect. The 

 observation of these needs to be supplemented by a 

 knowledge, much more difficult to obtain, of the con- 

 ditions of uneducated infancy and childhood of the 

 intellectual imbecilities of old age of the deficiencies 

 and aberrations of the idiot and lunatic of the mind 

 of the rustic or of the factory operative, his life a 

 machine of manual labour. Not only the subjects of 

 thought, but the power, methods, and rates of thinking 

 are presumably as diverse in these several cases as are 

 the conditions themselves. In most of them the 

 materials on which the mind acts are fewer and more 

 simple, and their combinations proportionally less 

 complex. Admitting exceptions for certain forms of 

 lunacy, we may presume the succession of mental 



