On Vision. 353 



hot vet seen a lamp, excepting the wire-gauze one of Sir H. 

 Davy, which in iny opinion deserves the name of a saftly-lump ; 

 and "tliat this is the decided opinion of persons interested in the 

 coal trade, is evident from the wire-gauze lamp being used in 

 exclusion of every other kind, in almost every colliery in this 

 country, in which fire-damp prevails. 

 I am, sir. 



Your very obedient humble servant, 



John Hodgson. 



LXXI. On Vision. By Mr. W. Pater., 



To Mr. Tiiloch. 



SfR, — iVIk. Horn, in his Observations on the Cosmogony of 

 Moses, has l)een so ol)!iging as to give his ideas on the seat of 

 vision, concluding "that the optic images are formed by caus- 

 tic reflection and exhibited in the middle of the vitreous humour, 

 and thus the optic impression and position of the tangible ob- 

 ject are reconciled." I will confess I do not exactly understand 

 what is meant by caustic reflection, and therefore shall make no 

 remarks upon it ; nor should I have ])articularly noticed the 

 other part of the opinion, had it not brought to my recollection 

 a correspondence I held with an acquaintance of mine, about 

 five-and-forty years ago, who had formed an idea that the eyQ 

 sees objects placed before it without any medium being necessary, 

 and th.it light merely renders bodies visible by diftiision over 

 their surfaces, he having no notion whatever that the light must 

 pass from the surface, or point illuminated, to the eye, to pro- 

 duce vision. Now it appears to me that Mr. Horn's theory is 

 founded upon some such idea, otherwise where is the necessity 

 of supposing that the rays are reflected from the nerve to form 

 images in the middle of the vitreous humour? because, if images 

 were formed in the vitreous humour, which seems contrary to 

 the nature of transparent fluids, still the rays of light nmst be 

 reflected back aqain from those images to the optic nerve to pro- 

 duce vision, because vision is a sensation produced by the action 

 of Hc[lit v[joa a itcrve, or nerves, adaptefl to receive excitement 

 from light. No part of the body is possessed of sensibility but 

 what has nerves, or is nervous, — the nerves alone being sentient ; 

 cousctjuently were light capable of being collected in the trans- 

 parent vitreous humour so as to form images in its centre, still, 

 those images coifld not be perceived there unless the vi- 

 treous humour were nervous, which is not the case ; and there- 

 fore, if these images were formed there, the li<iht must be re- 

 Vol. 18. No. 223. JVo^. 18UJ. Z ^ fleeted 



