538 INDUCTION. 



ciples. The quadrature of the cycloid is said to have been 

 first effected by measurement, or rather by weighing a 

 cycloidal card, and comparing its weight with that of a piece 

 of similar card of known dimensions. 



6. To the foregoing examples from physical science, 

 let us add another from mental. The following is one of the 

 simple laws of mind : Ideas of a pleasurable or painful cha- 

 racter form associations more easily and strongly than other 

 ideas, that is, they become associated after fewer repetitions, 

 and the association is more durable. This is an experimental 

 law, grounded on the Method of Difference. By deduction 

 from this law, many of the more special laws which expe- 

 rience shows to exist among particular mental phenomena 

 may be demonstrated and explained : the ease and rapidity, 

 for instance, with which thoughts connected with our passions 

 or our more cherished interests are excited, and the firm hold 

 which the facts relating to them have on our memory; the 

 vivid recollection we retain of minute circumstances which 

 accompanied any object or event that deeply interested us, 

 and of the times and places in which we have been very happy 

 or very miserable ; the horror with which we view the acci- 

 dental instrument of any occurrence which shocked us, or the 

 locality where it took place, and the pleasure we derive from 

 any memorial of past enjoyment; all these effects being pro- 

 portional to the sensibility of the individual mind, and to the 

 consequent intensity of the pain or pleasure from which the 

 association originated. It has been suggested by the able 

 writer of a biographical sketch of Dr. Priestley in a monthly 

 periodical,* that the same elementary law of our mental con- 

 stitution, suitably followed out, would explain a variety of 

 mental phenomena previously inexplicable, and in particular 

 some of the fundamental diversities of human character and 

 genius. Associations being of two sorts, either between 

 synchronous, or between successive impressions ; and the 

 influence of the law which renders associations stronger in 



* Since acknowledged and reprinted in Mr. Martineau's Miscellanies. 



