248 Obituary Notices of Fellows deceased. 



or strontium salt. The crystallised hydrates Ca0 2 8H 2 and 

 Sr0 2 8H 2 were obtained, as well as two other hydrates of strontium 

 dioxide crystallising with 10 and 12 molecules of water respectively. 

 It was shown that all these hydrates lost their water at 100, and 

 became changed into the anhydrous dioxides, which were shown to 

 be buff-coloured or colourless powders soluble in dilute acids without 

 evolution of oxygen. 



Conroy's next communication was a physical one, on the " Polariza- 

 tion of Light by Crystals of Iodine " (" Proc. Eoy. Soc.," 1876, p. 147). 

 It was observed that the light reflected from the surface of a layer of 

 iodine is polarized, and that the position of the plane of polarization 

 is not of necessity either perpendicular to or parallel with the plane of 

 incidence, but bears a definite relation to some direction within the 

 crystal. The light transmitted by thin films of iodine was also found 

 to be polarized in a plane perpendicular to that of the light polarized 

 by reflection. In the case of crystals, which are rhomboidal plates 

 belonging to the rhombic system, when the long axes of the crystals 

 are perpendicular to or parallel with the plane of incidence, part of 

 the light reflected from their surface is polarized in the plane of 

 incidence and part in a plane at right angles to the long axes of the 

 crystals. It was further shown that when a ray of light passes 

 normally through such a crystal, it is divided into two rays, polarized 

 respectively parallel with and perpendicular to the same crystallo- 

 graphic axis, and the one whose plane of polarization is parallel with 

 this axis suffers the less absorption. 



This was followed by two papers on the " Absorption Spectra of 

 Iodine" (" Proc. Eoy. Soc.," 1876, p. 45, and "Phil. Mag," 1877). It 

 was shown that the absorption spectra of thin films of solid iodine 

 are very similar to those given by alcoholic solutions of iodine, the 

 whole of the blue end of the spectrum being cut off; and that 

 absorption extends further towards the red as the thickness of the 

 film, increases, till at length only light of about wave-length 650 

 (near C) passes, which in turn is also cut off. Liquid iodine proved 

 to be more transparent, and gave more absorption of the middle 

 part of the spectrum than solid iodine. The action of light on 

 solutions of iodine in alcohol was further shown to resemble that 

 on solid iodine. The absorption of solutions in carbon bisulphide and 

 other liquids of that class proved to bear the same relation to the 

 absorption spectrum of the vapour as the spectrum of the solution of 

 a coloured gas does to that of the gas. 



In a memoir " On the Light Reflected by Potassium Permanganate " 



' ("Phil. Mag.," 1878, p. 454), Conroy described a study of the surface 



colours afforded by the crystals of this salt at varying angles of 



incidence, and showed that they altered with the surrounding medium, 



