10 REPORT — 1844. 



We understand that Professor Liebig, who regards these fluids and crystals as pecu- 

 liarly interesting, has made arrangements to investigate their nature, when taken out 

 of their cavities by Sir David Brewster, — an operation of extreme difficulty, owing to 

 the small size of the cavities which contain them, and the rapid disappearance of the 

 volatile fluid, which rises into a drop and contracts into a flat disc, as if it were 

 endued with vitality, finally vanishing and leaving a sediment behind it, which, when 

 breathed upon, again becomes fluid. 



On a singular Effect of the Juxtaposition of certain Colours under particular 

 circumstances. By Professor Wheatstone, F.R.S. 



Having had his attention drawn to the fact, that a carpet worked with a small 

 pattern in green and red, when illuminated with gas-light, if viewed carelessly, pro- 

 duced an efl^ect upon the eye as if all the parts of the pattern were in motion, he was 

 led to have several patterns worked in various contrasted pairs of colours ; and he 

 found that in many of them the motion was perceptible, but in none so remarkably 

 as those in red and green ; it appeared also to be necessary that the illumination 

 should be gas-light, as the effect did not appear to manifest itself in daylight, at least 

 in diffused daylight. He accounted for it by the eye retaining its sensibility for 

 various colours during various lengths of time. 



On the same Subject. 

 By Sir David Brewster, F.R.S. L. S)- E., Hon. M.R.I.A. ' 



Sir David Brewster stated that he and Prof. Wheatstone had brought to York 

 separate communications on this experiment, with specimens of the rug-work in 

 which it is best exhibited. Having seen Prof. Wheatstone's specimens, he had been 

 induced to limit his communication to a few observations on Prof. Wheatstone's 

 paper. When Sir D. Brewster came to York, he was not aware of the phsenomena 

 taking place with any other colour but red and green. Prof. Wheatstone had, how- 

 ever, shown him that red and blue answered equally well ; and he had received letters 

 from two ladies m Scotland, who had not only found that red and blue exhibited the 

 phaenomenon, but had both given the probable explanation of their doing so, by 

 ascribing it to the blue becoming green in the yellow light of the candle. 



In order to give an explanation of what has been called by some the fluttering 

 hearts, from one of the colours having the shape of hearts, Sir David Brewster men- 

 tioned an experiment for the purpose of showing that any fixed object will appear to 

 move on the ground upon which it is fixed, when the light which illuminates it is 

 constantly changing its position and intensity. This experiment consists in moving 

 a candle rapidly in all directions, in front of a statue. The varying lights and sha- 

 dows produce varying expressions, which give the appearance of life and motion to 

 the features of the statue. Now, in the case of the vibrating hearts, the mixture of 

 the red and green, whether seen as direct or as accidental impressions, produces suc- 

 cessions of light and shadow which give the appearance of motion to the figure upon 

 the red or green ground. This effect is greatly increased by that remarkable pro- 

 perty of oblique vision, in which the retina increases in sensibility as the point im- 

 pressed is removed from the foramen centrale. Hence when we look fixedly at one 

 of the vibrating hearts, it nearly ceases to vibrate, while the others, which are seen 

 obhquely, vibrate with greater distinctness. The pheenomenon has been stated to 

 be invisible in daylight ; but Sir David Brewster mentioned that he had, that morn- 

 ing, found that it took place in daylight, provided the coloured surface was illumi- 

 nated from a small hole in the shutter of a dark room. The experiment, indeed, he 

 found to fail even in candlelight, if the illumination proceeded from a great number 

 of lights, or from a mass of light producing a quaquaversiis illumination like that of 

 the sky. He referred also to the effects produced by coloured glasses, and mentioned 

 some facts regarding the unequal absorption of the two colours, which, in drawing 

 conclusions from such experiments, required to be attended to. 



On the Accommodation of the Eye to Various Distances. 

 By Sir David Brewster, F.R.S. L. Sf E., Hon. M.R.I.A. 



He commenced by giving a sketch of the opinions of several philosophers as to 



