©N THE PHANTASMS OF NICOLAI, ^2^ 



II. 



Letter from a Correfpondent, containing Difquifitions on the Phan- 

 tnfms of Nicola I, and other Derangements of the Animal 

 Si/fiem. 



To Mr. NICHOLSON, 

 SIR, 



JL HE account publiflied in your laft number by Mr. Nicolai, The phantafms 

 of his feeing fpedres, appears not only to admit of an ex- be ^Tin^T''^ 

 planation on f«me of the laws of vifion with which we are 

 already acquainted, but may alfo lead to fome rational :iccount 

 of the grounds, on which the belief in apparitions, which lias 

 fo generally prevailed in all ages of the world, may be founded. 



If we look for a moment at the fun, and afterwards turn — ^''^'^ ^^^ '™- 



,■, , t n . 1 , 1 prelTions of vifi- 



our eyes on the blue iky, or throw them upon the ground, we yg objefts on 

 perceive a black fpot of the apparent fize of that luminary, the eye. 

 This fpot will by degrees affume a faint green colour, then be- 

 comes red; and if we pay attention to thefe phenomena, we 

 fl»all find tlie green and red colours alternate, becoming gra- 

 dually more faint, till they wholly difappear. 



If the eye be directed for fome time towards a window, and Inftance of a 

 then covered by the hand, the bars will firft appear luminous, 

 and the fquares dark, and then the contrary, and this will al- 

 ternate till the whole image gradually faints away. 



Ti-efe are termed ocular fpedra, and have been fuppofed Thefe ocular 

 lo depend on the alternate tenfion and relaxation of the fibres obvio'us ^mtht 

 of which the reti'iiaare compofed. They refemble the trem-ftjte of dtbility 

 bJing of an over-fatigued mufcle, in which one fet of fibres ""^^^'^^^^^ 

 attempts to relieve the exertions of another. Thefe pheno- 

 mena are moft obvious after the eye has been fatigued by long 

 continued exertion. They are more readily obferved in the 

 evening than the morning, and the fpedra of the fetting are 

 more eafily caught than of the meridian fun. 



In certain ftates of bodily debility, whether produced by Spontaneous oc- 



the abfence of volition, or by difeafe, they are known fpon-*"''^^"':^°^'^P^*^ 

 T.^ni-, 1 tra intheftateof 



taneoully to occur. In the former itate, which may be termed reverie. 



reverie, when a perfon attends {lightly to the impreflions of his 



fenfes, without attempting to regulate them by his will, as 



when a perfon looks carelefsly in the fire during twilight, the 



infinite 



