It is difficult [he said] to argue with an author whose mind is filled with a medium of so fickle and vibratory a nature. Were we to take the trouble to refute him, he might tell us, _My opinion is changed_, and _I have abandoned that hypothesis, but here is another for you_. We demand if the world of science which Newton once illuminated is to be as changeable in its modes as the world of taste, which is directed by the nod of a silly woman or a pampered fop? Has the Royal Society degraded its publications into bulletins of new and fashionable theories for the ladies who attend the Royal Institution? _Proh pudor!_ Let the Professor continue to amuse his audience with an endless variety of such harmless trifles, but, in the name of science, let them not find admittance into that venerable repository which contains the works of Newton, and Boyle, and Cavendish, and Maskelyne, and Herschel. Young’s most famous experiment of stopping the rays which passed on one side of a thin card exposed to a sunbeam in a dark chamber Brougham threw aside, with the assertion that the experiment was inaccurately made. Dr. Young replied: The reviewer has here afforded me an opportunity for a triumph, as gratifying as any triumph can be where an enemy is so contemptible. Conscious of inability to explain the experiment, too ungenerous to confess that inability, and too idle to repeat the experiment, he is compelled to advance the supposition that it was incorrect. ‘Let him make the experiment, and then deny the result if he can.’ He took no special means to make his answer known, and only one copy of his reply was sold. The poison sank deep into the public mind, and Dr. Young’s researches remained comparatively unnoticed until Arago, in 1815, when reporting upon the optical discoveries of Fresnel, showed that a greater discoverer than Newton had anticipated the researches of the French philosopher. Dr. Young gives the following account of his discovery of the general law of the interference of light: