PAB re 0 bury BRagal Baeidly Been TT Rot 
- VI. Between F anda point 4 from F towards G, the colour appears 
to vary from the neutral tint to pure blue, while the brightness in- 
creases, and reaches a maximum at 2 from F towards G, and then 
diminishes towards the more refrangible end of the spectrum, the 
urity of the colour being apparently the same throughout. 
VII. The theory of colour-blind vision being “‘ dichromie,”’ is con- 
firmed by these experiments, the results of which agree with those 
obtained already by normal or “ ¢richromic’’ eyes, if we suppose the 
‘red’ element of colour eliminated, and the “green” 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, isa red, whose relations to vermilion, ultramarine, and emerald- 
green are expressed by the equation 
D=1-198V +0:078U—0:276G, 
where D is the defective element, and V, U and G the three colours 
named above. 
April 26.—Sir Benjamin C. Brodie, Bart., President, in the Chair. 
The followmg communication was read :— 
** Note on Regelation.”” By Michael Faraday, D.C.L., F.R.S. &e. 
_ The philosophy of the phenomenon now understood by the word 
Regelation is exceedingly interesting, not only because of its relation 
to glacial action under natural circumstances, as shown by Tyndall 
and others, but also, and as I think especially, in its bearmgs upon 
molecular action ; and this is shown, not merely by the desire of dif- 
ferent philosophers to assign the true physical principle of action, 
but also by the great differences between the views which they have 
taken. 
Two pieces of thawing ice, if put together, adhere and become 
one ; at a place where liquefaction was proceeding, congelation sud- 
denly occurs. ‘The effect will ke place in air, or in water, or in 
vacuo. It will occur at everypoint where the two pieces of ice 
