In the Report of the Seventh Meeting of the British Association, and in that of the Eighth Meeting, Sir David Brewster has given a short account of experiments which have led him to infer the existence of a polarity , in the rays of homogeneous light, having regard only to the sequence of colours in the spectrum. I am aware that Sir David Brewster has announced his intention of publishing a more elaborate paper upon these experiments. But as the leading facts of the experiments have now been communicated to the public nearly two years, and by Sir David Brewster himself, and as the accounts have been sufficiently explanatory to enable any other person to repeat the experiments, and as various persons have in consequence repeated them, there cannot, I conceive, be the most trifling impropriety in making the whole subject a matter of discussion, experimental and theoretical