362. ON DEPARTURES FROM FEESNEL'S LAWS OF REFLEXIC [Philosophical Magazine, Vol. xxm. pp. 431—439, 1912.] IN the summer of 1907, in connexion with my experiments upo flexion from glass at the polarizing angle*, I made observations also the diamond, a subject in which Kelvin had expressed an interest. I known from the work of Jamin and others that the polarization of reflected from this substance is very far from complete at any anj incidence, and my first experiments were directed to ascertain whethe] irregularity could be plausibly attributed to superficial films of fc matter, such as so greatly influence the corresponding phenomena i: case of waterf. The arrangements were of the simplest. The light a paraffin flame seen edgeways was reflected from the diamond and exai with a nicol, the angle being varied until the reflexion was a minimum. In one important respect the diamond offers advantages, in comps for instance, with glass, where the surface is the field of rapid che changes due presumably to atmospheric influences. On the other the smallness of the available surfaces is an inconvenience which, ho-\ is less felt than it would be, were high precision necessary in the me; ments. Two diamonds were employed—one, kindly lent me by Sir W. Cr mounted at the end of a bar of lead, the other belonging to a lady's No particular difference in behaviour revealed itself. The results of repeated observations seemed to leave it improbable any process of cleaning would do more than reduce the reflexion a polarizing angle. Potent chemicals, such as hot chromic acid, iru employed, but there is usually a little difficulty in the subsequent j ration. After copious rinsing, at first under the tap and then with dif water from a wash-bottle, the question arises how to dry the surface, ordinary wiping may be expected to nullify the chemical treatment; * Phil. Mag. Vol. xvi. p. 444 (1908); Scientific Papers, Vol. v. p. 489. t Phil. Mag. Vol. xxxin. p. 1 (1892); Scientific Papers, Vol. in. p. 496. with what Prof. Michelson has to tell of his own achievements and experiences, but it seems desirable that they should be set right. train passing at high speed at a distance of 'not more than 150 yardi almost inaudible. The wheels were in full view, but the situation was such that the line of -v passed for most of its length pretty close to the highly heated ground. It seemed clear tha sound rays which should have reached the observers were deflected upwards over their h which were left in a kind of shadow.kness, of which the first is similar to the final uniform medium, and the second similar to the initial uniform medium. •Of the three partial reflections the first and third are similar, but the secondo guide the lantern-plates into position, and thus to ensure their subsequent exact superposition by simple mechanical means.