i68 



ON SLEEP, DREAMING, 



worthy of notice ; that of Epicurus, because of its ingenuity, ahd that 

 of Aristotle, because it has descended to the present times. 



According to the Epicurean hypothesis of sensation, all the organs of 

 external sense' are stimulated to their appropriate functions, by the frictiott 

 of an effluvium or emanation thrown off from the body perceived. This 

 doctrine, which still holds good, and is uniformly employed in modern 

 times to explain the sense of taste and smell, was equally extended by 

 Epicurus to those of sight and hearing : the former being supposed to de- 

 pend upon an effluvium of exquisitely .fine fdms, images or species, as 

 they were technically called, perpetually issuing in' every direction from 

 every existing substance, son»ewhat in tbe manner in which snakes and 

 grasshoppers cast off their skins annually, but almost infinitely finer, and 

 altogether invisible. And as these rush against the eye, they were con- 

 ceived to convey to it a perfect image of tlie object from which they are 

 ejected. While sound was supposed to be excited in like manner by par- 

 ticles of a peculiar kind thrown off from the sonorous body, and rousing 

 the ears by their appropriate stimulus. 



These effluvia of every kind were conceived to be so exquisitely attenu- 

 ate that they can pass, as light, heat, or electricity does, through a variety 

 of sohd bodies, without being destroyed in their passage. The effluvia or 

 pellicles of vision were supposed not unfrequently to arise from the very 

 bodies of those that have been long buried ; and to be capable not 

 only of transpiercing the soil in which they are inhumed, and of stiniiu- 

 lating the organs of external sight, but of winding through the sub- 

 stance of the flesh, and of stimulating the soul itself in the interior 

 of the animal frame, especially when in a state of sleep, in which the 

 external sense is closed, or of deep abstraction, in which it is inatten- 

 tive ; and thus of presenting to the soul in its naked state, as it may 

 be called, pictures of objects no longer in existence. And hence 

 these philosophers with great ingenuity, though, as it now appears, with 

 great incorrectness, undertook to solve many of the most difficult pro- 

 blems in nature ; accounted for the casual appearance of spectres in the 

 gloom of solitude and retirement, and directly unfolded to the world the 

 "stuff that dreams are made of." 



It is needless to point out the errors of this system, for it has long sunk 

 into disuse, never to rise again. And 1 shall therefore proceed to the rival 

 hypothesis of Aristotle, which, though equally unfounded in fact, has been 

 fortunate enough to descend to modern times, and to have met with very 

 powerful advocates in M. Wolffs and M. Formey.j It was the doctrine 

 of Aristotle, that external sensations not only produce by their stimulus a 

 variety of intellectual forms or images in the sensory, somewhat similar 

 to the ideas of Plato, and for all practical purposes not very dissimilar to 

 what is meant by ideas in the present day, but that these forms or ideas are 

 themselves capable of producing another set of forms or ideas, though of a 

 more airy and visionary kind : " 



As every shadow has itself a shade. 



And to this secondary set, these slighter and more attenuate pictures of 

 things, he gave the name of phantasms. In the opinion of this philoso- 

 pi;er, dreams consist alone of these phantasms, or mere creatures of the 

 imagination, first excited by sofne previous motion or sensation in the 



* Psychol. Empir. sec. 123. 



t Mem. de I'Acad. de Berh'n, ii. 316. 



