Ina] AND SYMBOLS. . 157 



great-leaved horse-shoe bat. If you proceed with torches they 

 will become so eager to escape from your light that they will 

 annoy you exceedingly by flapping against your face in their 

 eagerness to escape into a congenial darkness. How much they 

 remind one of those ignorant bigots who, when the torch of 

 truth is carried into the recesses of superstition, dash in wild 

 exasperation against the enlightener, and do their utmost to seek 

 intellectual gloom ! GA. 



Accidental Images. 



A coloured object being placed upon a black ground, if it is 

 steadily looked at for some time, the eye is soon tired, and the 

 intensity of the colour enfeebled; if now the eyes are directed 

 towards a white sheet, or to the ceiling, an image will be seen 

 of the same shape as the object, but of a complementary colour ; 

 that is, such a one as united to that of the object would form 

 white. For a green object the image will be red ; if the object 

 is yellow, the image will be violet. Accidental colours are of 

 longer duration in proportion as the object has been more 

 brilliantly illuminated and the object has been longer looked 

 at. When a lighted candle has been looked at for some time, 

 and the eyes are turned towards a dark part of the room, the 

 appearance of the flame remains, but it gradually changes 

 colour ; it is first yellow, then it passes through orange to red, 

 from red through violet to greenish blue, which is gradually 

 feebler until it disappears. If the eye which has been looking 

 at the light be turned towards a white wall, the colours follow 

 almost the opposite direction ; there is first a dark picture on 

 a white ground, which gradually changes into blue, is then 

 successively green and yellow, and ultimately cannot be dis- 

 tinguished from a white ground. The reason of this phenomenon 

 is doubtless to be sought in the fact that the subsequent action 

 of light on the retina is not of equal duration for all colours, 

 and that the decrease in the intensity of the subsequent action 

 does not follow the same law for all colours. But the illusion 

 is very startling ; and it bears some analogy to the occasional 

 remarkable creations of the memory when, in reproducing 

 certain events and personages, it presents them in forms some- 



