L imit of the I mag {nation. 1 6 5 



and by analogous treatment give rise to additional 

 new conceptions. 



But although we evolve truthful new conceptions 

 from previous ones by these purely mental methods, 

 there is a limit to the number capable of being evolved 

 from a limited stock of ideas, because the number of 

 combinations and permutations of such a stock, though 

 usually large, are themselves limited. The number 

 however is large in proportion to the degree of essen- 

 tial importance of the ideas, and is greatest when we 

 employ those of the fundamental principles of nature, 

 already referred to ; for instance a greater number of 

 new ideas have been evolved by means of appropriate 

 mental processes from the law of gravitation and 

 from that of electro-magnetism than from any minor 

 truth in science. Persons therefore who are the least 

 familiar with great demonstrable principles are usually 

 the least able to conceive new truthful ideas of intrin- 

 sic importance, or to draw new verifiable inferences of 

 much theoretical value. 



Every inventor and student knows that he continu- 

 ally requires new materials of thought, and if he does 

 not obtain them, an obstacle, like a wall of adamant, 

 rises before his mind in all directions, and prevents 

 his forming new ideas. That also which is true of 

 each individual is true of the collection of individuals, 

 mankind ; if new truths are not obtained, the thoughts 

 of men flow in circles, and mental progress ceases. 

 The mental characteristics of sequestered communr 

 ties in remote isolated districts, are examples of this 



