and Coloured Shadows. 429 



the opposite flavour, by means of strong tea without sugar 

 in one case, and sugar without tea in the other, continued 

 for a sufficient time to produce the effect. — Epicures have 

 generally some acquaintance with this branch of philosophy, 

 and they would be enabled to add to their gratifications by 

 studying it further ; if we wish to make the most of our 

 pleasures, discretion and moderation must regulate their 

 enjoyment. 



It appears, then, that if the sight preserves an uniform 

 state of intensity, it is an exception to a general law ; but, 

 that this anomaly has no existence may be proved by the 

 most direct evidence. 



I have noticed in a former paper, the very striking ex- 

 periments of going from a strong to a weak light, with 

 which all of us must be well acquainted ; the total insen- 

 sibility of the eye, under these circumstances, proves more 

 than is at present required of us ; we are now only called 

 upon to shew, that the sensibility of the eye is lessened by 

 the continued action of light of the same intensity. 



Much confusion has arisen among writers upon the 

 subject of accidental colours, in consequence of their 

 having made no distinction between pure red and the 

 different shades of colour produced by a mixture of red 

 and violet, which approach, more or less, to crimson, and, 

 when diluted with white light, to pink : these mixtures 

 produce accidental colours of the various shades of green, 

 approaching the nearer to blue as the proportion of violet 

 is less in the primary colour; whereas the red of the 

 spectrum, when pure, constantly produces a blue accidental 

 colour. — When red is diluted with white light, it forms 

 the various shades of pale red, some of which are frequently 

 mistaken for orange, and thus furnish another source of 

 confusion. — There is also a want of distinction between the 

 various shades of blue ; and, I mention it here, because it 

 is probable, that it led to that part of the theory adopted 

 by Mr. Tomlinson, which makes violet a compound of blue 

 and red. —The blue which forms white light with red is 

 the bright shade of this colour which adjoins the white 

 central light, when the spectrum of the sun is received 

 upon a screen placed at a short distance from the prism ; 

 but, besides this blue, which is rather of a light colour, it 



