| Extreme red | 458,000,000,000,000 | waves per second. |
| Red | 477,000,000,000,000 | waves per second.„ |
| Orange | 506,000,000,000,000 | waves per second.„ |
| Yellow | 535,000,000,000,000 | waves per second.„ |
| Green | 577,000,000,000,000 | waves per second.„ |
| Blue | 622,000,000,000,000 | waves per second.„ |
| Indigo | 658,000,000,000,000 | waves per second.„ |
| Violet | 699,000,000,000,000 | waves per second.„ |
| Extreme violet | 727,000,000,000,000 | waves per second.„ |
Whatever theory we may adopt to explain the phenomena of light, we arrive at conclusions that strike the mind with astonishment and admiration. According to the corpuscular hypothesis, it was supposed that the molecules of light were endowed with the power of attraction and repulsion, that they possessed poles and centres of gravity like the earth, and that they had other physical properties that could only be given to ponderable matter. Starting with these notions, it is difficult to divest oneself of the idea of sensible size, or to induce the mind to conceive particles so extremely small as those of light would necessarily be if the theory of emission were accepted. If a particle of light weighed a grain, it would produce by means of its enormous velocity the effects of a cannon-ball weighing 120 lbs., travelling at the rate of 300 yards per second. How infinitely small would be these particles, seeing that the most delicate optical instruments are submitted to their action for years without being injured!
If we are astonished at the extreme smallness and prodigious rapidity of the luminous molecules whose existence is necessitated by the corpuscular theory, the numerical results of the undulatory hypothesis are not less surprising. The extreme smallness of the distance between the waves, and the inconceivable quickness of their undulations, although both are easily calculated, must raise in the mind of the student feelings of the utmost wonder and admiration.
