WE know not for how many ages colours have been developing. "In the beginning, darkness was upon the face of the deep." The physical properties of light are probably the deepest and most interesting studies in physical science. I only touch upon light as the acting energy or life, causing, in its struggles with darkness, not only the varieties of colour around us, but the colour even of light itself, as colours arise from rays of light exercising different influences.

The primitive laws of any science should be capable of succinct statement, but in combination with others they become more complex and delicate, and error is proved if in the developments they do not echo each other. If, therefore, musical harmonies are correctly gained, the same laws will develope harmonies of colour, and will agree with the colours of the rainbow, the circle of which is divided by the horizon. All who are interested in the laws which regulate these two sciences will doubtless know the interesting lectures delivered by W. F. Barrett (Professor of Experimental Physics in the Royal College of Science, Dublin), and the article written by him and published in the Quarterly Journal of Science, January, 1870, entitled "Light and Sound; an examination of their reputed analogy, showing the oneness of colour and music as a physical basis." I will quote shortly from the latter for the benefit of those who may not have met with it. "The question arises, Has all this æsthetic oneness of colour and music any physical foundation, over and above the general analogy we have so far traced between light and sound? We believe the following considerations will show, not only that it has some foundation, but that the analogy is far more wonderful than has hitherto been