68 GENERAL YIEW AND BASIS OF SCIENTIFIC RESEARCH. 



accordance with these laws, the impressions made upon 

 the brain by sensations, eruptions, and ideas, are linked 

 together by association and habit, in trains or diverging 

 series ; and in a well-arranged mind, much in the same 

 order as the existences which they represent, are bound 

 together by the laws and principles of nature. The great 

 truths of nature, therefore, should be the ' central ideas ' 

 of mind. 



The action of memory in recalling ideas depends 

 essentially upon this latent association of impressions. 

 When any idea in a series is excited, it tends to raise 

 both c contiguous ' and ' similar ' ideas ; especially the 

 former, because the bond is the strongest. Thus, that of 

 redness in metals tends to raise the contiguous ideas which 

 constitute the compound conception of copper, and also 

 those of any other substance of similar colour. The idea 

 of magnetism tends to raise the idea of iron, &c., and 

 conversely, the idea of iron tends to raise that of mag- 

 netism ; and the action is called ' associative suggestion 

 of ideas.' 



The degree of power of suggestion of ideas depends 

 upon a number of circumstances, and is different in every 

 different case. For instance, in the mind of a scientific 

 man the idea of magnetism is more suggestive of that of 

 iron than that of iron is of magnetism, because in the first 

 case iron is the only substance which is strongly magnetic, 

 whilst in the second many other properties besides mag- 

 netism are closely associated with iron. In recalling a 

 compound idea or group of ideas, we usually at first realise 

 some chief or more simple idea which forms an essential 

 part of it, and this recalls the less powerfully impressed 

 ones. 



During the act of associative suggestion of ideas, in 

 the ordinary current of thought and reflection in quiet 



