THE SENSATION OF SIGHT. 249 



from the middle of the field ; and, on the other hand, 

 when they appear white here, are red to direct vision. 

 These inequalities of the retina, like the others men- 

 tioned in the former essay, are rectified by the con- 

 stant movements of the eye. We know from the pale 

 and indistinct colours of the external world as usually 

 seen, what impressions of indirect vision correspond to 

 those of direct ; and we thus learn to judge of the colours 

 of objects according to the impression which they would 

 make on us if seen directly. The result is, that only 

 unusual combinations and unusual or special direction of 

 attention enable us to recognise the difference of which I 

 have been speaking. 



The theory of colours, with all these marvellous and 

 complicated relations, was a riddle which Groethe in vain 

 attempted to solve ; nor were we physicists and physio- 

 logists more successful. I include myself in the number ; 

 for I long toiled at the task, without getting any 

 nearer my object, until I at last discovered that a 

 wonderfully simple solution had been discovered at the 

 beginning of this century, and had been in print ever 

 since for any one to read who chose. This solution was 

 found and published by the same Thomas Young * who 

 first showed the right method of arriving at the in- 

 terpretation of Egyptian hieroglyphics. He was one 

 of the most acute men who ever lived, but had the 

 misfortune to be too far in advance of his contempo- 

 raries. They looked on him with astonishment, but could 

 not follow his bold speculations, and thus a mass of his 

 most important thoughts remained buried and forgotten 

 in the ' Transactions of the Eoyal Society,' until a later 

 generation by slow degrees arrived at the rediscovery of 

 his discoveries, and came to appreciate the force of hia 

 arguments and the accuracy of his conclusions. 



1 Born at Milverton, in Somersetshire, 1773, died 1829. 



