486 



Sir J. Conroy. 



[Mar. 3, 



Pritchard, Urban, M.D., F.R.C.S. S 

 Radcliffe, Charles Bland, M.D., 



F.R.C.P. T 

 Ransome, Arthur, M.A., M.D. 



Ranyard, Arthur Cowper,F.R. A. S. T 



Rawlinson, Robert, O.B., M.I.O.E. M\ 



Reinold, Prof. Arnold William, Y 



M.A. ¥ 

 Rodwell, George F., F.R.A.S., 



F.C.S. ^ 



Samuelson, Bernhard, M.I.O.E. "Y* 

 Spiller, John, F.C.S. 



The following Papers were read : — 



Stoney, Bindon Blood, M.A. 



M.LC.E. 

 Tidy, Prof. Charles Meymott, 



M.B., M.R.C.S., L.S.A. 

 Traquair, Ramsay H., M.D. ■ 

 Warren, Charles, Lieut. -Col. R.E. 

 Watson, Rev. Henry William, M.A. 

 Williams, Charles Theodore, M.A., 



M.D., F.R.C.P. 

 Wright, Charles R. Alder, D.Sc. 

 Wright, Edward Perceval, M.A., 

 M.D, F.L.S, 



I. " Some Experiments on Metallic Reflexion. No. II." By 

 Sir John Conroy, Bart., M.A. Communicated by Professor 

 Stokes, Sec. R.S. Received February 12, 1881. 



Professor Stokes did me the honour of communicating to the Royal 

 Society a short paper (" Proc. Roy. Soc," vol. 28, p. 242) giving an 

 account of some determinations I had made of the values of the prin- 

 cipal incidence for, and the principal azimuth of, red light, when 

 reflected by a gold plate in contact with air, water, and carbon 

 bisulphide. 



These experiments I have continued, Using light of different refran- 

 gibilities, and gold and silver plates, and also thin films of these metals. 



The observations were made by causing a beam of light which had 

 been polarised elliptically, by passing through a nicol with its prin- 

 cipal section at an angle of 45° with the plane of incidence, and a 

 " quarter undulation plate," with one of the neutral axes in that plane- 

 to fall on the metal plate, and then altering the angle of incidence till 

 the reflected light was plane polarised. 



The angle of incidence at which this was the case was different, 

 according as one or other of the neutral axes of the quarter plate was 

 in the plane of incidence, and the mean of these two values was taken 

 as the true principal incidence. 



The goniometer used in these experiments was described in the 

 former paper, but had an additional vertical divided circle attached to 

 the inner end of the tube fixed to the collimator arm, in order to 

 facilitate the adjustment of the quarter plate, and to permit the plate 

 being changed, without the necessity of determining each time the 

 position of the neutral axes, 



Brewster's law, that the tangent of the angle of polarisation is equal 



