486 



obtained already by normal or " trichromic" eyes, if we suppose the 

 "red" element of colour eliminated, and the "green 5 ' and "blue" 

 elements left as they were, so that the " red-making rays" though 

 dimly visible to the dichromic eye, excite the sensation not of red 

 but of green, or as they call it, " yellow." 



VIII. The extreme red ray of the spectrum appears to be a suf- 

 ficiently good representative of the defective element in the colour- 

 blind. When the ordinary eye receives this ray, it experiences the 

 sensation of which the dichromic eye is incapable ; and when the di- 

 chromic eye receives it, the luminous effect is probably of the same 

 kind as that observed by Helmholtz in the ultra-violet part of the 

 spectrum a sensibility to light, without much appreciation of colour. 



A set of observations of coloured papers by the same dichromic 

 observer was then compared with a set of observations of the same 

 papers by the author, and it was found 



1 . That the colour-blind observations were consistent among them- 

 selves, on the hypothesis of two elements of colour. 



2. That the colour-blind observations were consistent with the 

 author's observations, on the hypothesis that the two elements of 

 colour in dichromic vision are identical with two of the three elements 

 of colour in normal vision. 



3. That the element of colour, by which the two types of vision 

 differ, is a red, whose relations to vermilion, ultramarine, and emerald- 

 green are expressed by the equation 



D=M98V + 0-078U-0-276G, 



where D is the defective element, and V, U and G the three colours 

 named above. 



IV. " Report to the Royal Society of the Expedition into the 

 Kingdom of Naples to investigate the circumstances of the 

 Earthquake of the 16th December 1857." By ROBERT 

 MALLET, Esq., C.E,, F.R.S. 



(Abstract.) 



The region examined in this expedition, embraces, in its widest 

 extent, most of the country between a line drawn from Terracina to 

 Gargano on the north, down to the Gulf of Taren turn on the south. 



