MEMOIR VI.] INVERSE VISION. 



rounded, impress us very differently. The want of uni- 

 son between such images and the things among which 

 they have intruded themselves, the anachronism of their 

 advent, or other obvious incongruities, restrain the mind 

 from delivering itself up to that absolute belief in their 

 reality which so completely possesses us in our dreams. 

 Yet, nevertheless, such is the constitution of man, the 

 bravest and the wisest encounter these fictions of their 

 own organization with awe. 



The visions of an Arab merchant have ended in tinct- 

 uring the daily life of half the people of Asia and Africa 

 for a thousand years. A spectre that came into the 

 camp at Sardis the night before the battle of Philippi 

 unnerved the heart of Brutus, and thereby put an end 

 to the political system that had made the Roman repub- 

 lic the arbiter of the world. A phantom that appeared 

 to Constantine strengthened his hand to that most diffi- 

 cult of all the tasks of a statesman, the destruction of an 

 ancient faith. 



Hallucinations are of two kinds those seen when the 

 eyes are open and those perceived when they are closed. 

 To the former the designation of apparitions, to the lat- 

 ter that of visions, may be given. 



In a physiological sense, simple apparitions may be 

 considered as arising from disturbances or diseases of 

 the retina; visions, from the traces of impressions en- 

 closed at a former time in the corpora quadrigemina and 

 optic thalami. 



From flying specks floating before us, the first rudi- 

 ments of apparitions, it is but a step to the intercalation 

 of simple or even grotesque images among the real ob- 

 jects at which we are looking; and indeed this is the 

 manner in which they always offer themselves, as resting 

 or moving among the actually existing things. 



