AND THE THEORY OF LIGHT. 61 



blue sky evidently did not reflect enough of light to pro- 

 duce blue. Blue was obtained best when there were white 

 clouds in the atmosphere. 



This is quite contrary to what was to have been ex- 

 pected. Had blue been obtained when the sky was blue 

 there would have been less confidence placed in the expe- 

 riment ; but although it would have created suspicion 

 about the blue, it would not have diminished the value of 

 the fact, that a different shade of colour had been obtained 

 by the motion of a white ray of light. The experiment 

 turning out as it has done leaves a stronger conviction on 

 the mind than ever, that blue is produced by pulsations of 

 light associated with darkness or shadow, and is not, as 

 has been considered, one of the elements of a compound 

 substance, but is rather itself a compound. 



At this stage of the investigation, after reflecting much 

 on the subject but without engaging in any more experi- 

 ments, I was so flrmly convinced of the truth of the theory 

 that I very hastily concluded that this experiment alone 

 completely established the vibratory nature of light, and 

 proved, without any question, the homogeneity of the 

 ether. There were no rays in the spectrum so diflicult to 

 account for as the blue and the purple, and having dis- 

 covered the origin and formation of these rays, there would 

 be no difficulty, I thought, in accounting for the others, nor 

 of explaining the nature of the prism, the rationale of the 

 rainbow, and the cause of what are called complementary 

 colours ; and after much labour and thought I was led to 

 the conclusion, from this and other experiments, that they 

 may be explained in an easy and simple manner. 



Effects of different velocities. 



92. Having remarked in the former experiment, that the 

 same slip of paper, moving with equal velocity in different 

 states of the weather, produced different shades of colour. 



