48 VOLUNTARY MOTIONS. SECT. IX. 3. 



excited thefe ideas repeatedly, you excite the idea 

 of their difference, which is that of another right- 

 angled triangle inverted over the former ; you are 

 faid to reafon upon this- fubject, or to compare your 

 ideas. 



Thefe ideas of recollection, like the mufcular mo- 

 tions above 1 mentioned, were originally excited by 

 the irritation of external bodies, and were termed 

 ideas of perception: afterwards the pleafure or 

 pain, that accompanied thefe motions, induced a 

 repetition of them in the abfence of the external 

 body, by which they were fir ft excited ; and then 

 they were termed ideas of imagination. At length 

 they become voluntarily practifed in fuccceflion or 

 in combination for the common purpofes of life;" 

 as when we make ourfelves matters of the hiftory of 

 mankind, or of the fciences they have inveftigat- 

 cd ; and are then called ideas of recollection ; and 

 are performed with ftrength and velocity in pro- 

 portion to the energy of the volition that excites 

 them, and the quantity of fenforial power. 



II. i. The mufcular motions above defcribed, 

 that are moft frequently obedient to the will, are 

 neverthelefs occaiionally caufable by painful or plea- 

 furable fenfation, as in the ftarting from fear, and 

 the contraction of the calf of the leg in the cramp. 



2. In like manner the fenfual motions, or ideas, 

 that are moft frequently connected with volition, 

 are neverthelefs occafionally caufable by painful or 

 pleafurable fenfation. As the hifiories of men, or 

 the defcription of places, which we have volunta- 

 rily taken pains to remember, fometimes occur to 

 us in our dreams. 



Hi. i. The mufcular motions that are generally 

 fubfervient to volition, are alfo occafionally caufa- 

 ble by irritation, as in ftretching the limbs after 

 fleep, and yawning. In this manner a contraction 

 of the arm is produced by paffing the electric fluid 



from 



