10 MR. J. SMITH ON THE ORIGIN OF COLOUR 



14. We are apt to think it easy to understand that red 

 and blue become green, or that red and black make a dark 

 dirty green^ for we see it often take place; but when we 

 ask ourselves the physical cause of such an effect as that 

 produced by our experiment, it is not so easy to discover 

 one; for according to the commonly received interpretation 

 of the laws of light there is not a sufficient cause for the 

 effect. Both images appear to be seen, but how can the 

 one be seen through the other, or how can they appear 

 transparent, but on the supposition that there are intervals 

 in the movements of the rays from the different objects ? 

 We have thus as it were the first step in an argument for 

 the undulatory or rather the vibratory motion of light. 



1^. In this experiment we have two sensations which 

 differ from each other on the retina, and yet before they 

 reach the sensorium are compounded into another sensa- 

 tion of a different character. Hence the question natu- 

 rally arises : If the composition of forces or of colours 

 takes place in the organs of vision so simply, does it not 

 presuppose a greater complexity in the laws of light, as 

 commonly taught, than is to be found in any other of the 

 works of God, to affirm that light is a compound hetero- 

 geneous substance not only requiring continual decompo- 

 sition but perpetual recomposition ? Is it not introducing 

 into the theory of light ideas as perplexing as the cycles 

 and epicycles which existed in astronomy before the time 

 of Copernicus ? 



16. After carefully considering the phenomenon in all 

 its bearings, the only satisfactory explanation I could 

 arrive at was, that the two insulated spots, one on the 

 one eye and the other on the other eye, could only be per- 

 ceived as one object not as two, for the impression at all 

 times received by two eyes of the same spot is single — 

 hence, although we have two eyes, we have virtually or 

 sensationallv but one retina — therefore in this case the 



