290 Mr. Tornlinson on the Theory of [Oct. 



I was engaged a portion of one evening a few weeks 

 since, on experiments on colour, after which I delivered a 

 lecture on combustion", wherein I had to exhibit the red fire 

 of the theatres, which burned vividly and brilliantly ; and, 

 after the lecture, I retired to bed somewhat fatigued, my 

 thoughts being occupied with the subjects that had engaged 

 them previous to the lecture, in mentally contriving various 

 forms and shades of the favourite green colour, for the next 

 evening's investigation. I had been in darkness above an 

 hour, and was probably just falling asleep, when I was 

 aroused by a vivid impression of the forms I had just before 

 determined in my mind, but the colours were not green, 

 but red, wearing a cloudy phosphorescent hue, and standing 

 out, a foot or two, apparently, from my eyes. As I am not 

 aware of any disordered action of my eyes, except an imper- 

 fect vision as to distant objects, generally large pupils, and 

 a sligl^t affection of amaurosis in the left eye, I can only 

 explain the above phenomenon on the assumption that the 

 ♦active impression of green in the mind, re-produced on the 

 retina the accidental impression of the fundamental tint. The 

 eyes, too, might have been, and probably were, fatigued by 

 the lecture, and the influence of the impression of the red 

 fire, combined with the employment of the eye previous to 

 to the lecture, must not be forgotten ; but, being very often 

 (once or twice a week) engaged in delivering chemical lec- 

 tures, I generally bestow but little attention on the effect 

 of brilliant experiments on my eyes. As I do not admit the 

 necessity of the oscillations of the retina, insisted on by M. 

 Plateau, in viewing these colours, I only admit his "impres- 

 sion according to time," with considerable modifications. 



8. In employing the red fire^ in my lectures, it has been 



* By a curious coincidence, the materials for the production of red fire are, 

 when properly mixed, a dark-green 9olour. I am not at piesent aware that any 

 importance is to he attached to this remark, hut a numher of analogous facts will 

 crowd upon the mind of the chemist, such as the alkalized oxide of manganese,, 

 wliich is of an opaque green colour, and when thrown into water produces a dark 

 transparent green, which speedily changes to red ; and I may mention, generally 

 the red and green hues, as in this case, indicative of the presence of manganic and 

 permanganic acid. The chemical compounds of oxygen and nitrogen, and the 

 interesting changes of colour produced hy saturating nitric acid with the binoxide ; 

 the action of nitric acid on copper ; the oxidation of steel, of silver leaf, &c., &c., 

 are all familiar instances which suggest themselves to my mind while writing this 

 note. It will be out of place here to entimerate them further. 



