174 



Prof. G. G. Stokes. On a remarkable [Feb. 26, 



IT. '* Note on a preliminary Comparison between the Dates of 

 Cyclonic Storms in Great Britain and those of Magnetic 

 Disturbances at the Kew Observatory." By Balfour 

 Stewart, M.A., LL.D., F.R.S., and Wm. Lant Car- 

 penter, B.A., B.Sc. Received February 11, 1885. 



We took the dates of thirty storms from Mr. Scott's paper entitled 

 " The Equinoctial Gales ; do they occur in the British Isles ? " in the 

 " Quarterly Journal of the Meteorological Society " for October, 1884, 

 and by the kindness of Mr. Whipple, of the Kew Observatory, were 

 enabled to make the comparison mentioned above. 



Out of these thirty storms, in twenty-three cases there is a distinct 

 magnetic disturbance, for the most part preceding the storm by some- 

 what more than a day. We do not, however, imagine that we have 

 thus proved the fact of such a connexion, but think the results we 

 have attained sufficient to justify us in pursuing the subject. 



February 26, 1885. 



THE TREASURER in the Chair. 



The Presents received were laid on the table and thanks ordered for 

 them. 



The following Papers were read : — 



L "On a remarkable Phenomenon of Crystalline Reflection." 

 By G. G. Stokes, M.A., Sec. R.S., Lucasian Professor of 

 Mathematics in the University of Cambridge. Received 

 February 25, 1885. 



Introduction. 



In a letter to me, dated March 29, 1854, the late Dr. W. Bird 

 Herapath enclosed for me some iridescent crystals of chlorate of 

 potash, which he thought were worth my examination. He noticed 

 the intense brilliancy of the colour of the reflected light, the change 

 of tint with the angle of incidence, and the apparent absence of 

 polarisation in the colour seen by reflection. 



The crystals were thin and fragile, and rather small. I did not see 

 how the colour was produced, but I took for granted that it must be 



