213 



by my brother's theory, published in the ' Proceedings ' for 

 May 1857. 



I believe the theory I have given above contains the true explanation 

 of one remarkable fact observed by Dr. Tyndall in connexion with the 

 beautiful set of phenomena which he discovered to be produced by 

 radiant heat, concentrated on an internal portion of a mass of clear 

 ice by a lens ; the fact, namely, that the planes in which the vesi- 

 cles extend are generally parallel to the sides when the mass of ice 

 operated on is a flat slab ; for the solid will yield to the " nega- 

 tive" internal pressure due to the contractility of the melting ice, 

 most easily in the direction perpendicular to the sides. The so-called 

 negative pressure is therefore least, or which is the same thing, the 

 positive pressure is greatest in this direction. Hence the vesicles of 

 melted ice, or of vapour caused by the contraction of melted ice, 

 must, as I have shown, tend to place themselves parallel to the sides 

 of the slab. 



The divisions of the vesicular layers into leaves like six-petaled 

 flowers is a phenomenon which does not seem to me as yet so easily 

 explained ; but I cannot see that any of the phenomena described by 

 Dr. Tyndall can be considered as having been proved to be due to 

 ice having mechanical properties of a uniaxal crystal. 



April 29, 1858. 

 J. P. GASSIOT, Esq., Vice-President, in the Chair. 



The following communications were read : 

 I. " An Account of the Weather in various localities during 

 the 15th of March, 1858 (the day of the Great Solar 

 Eclipse) ; together with Observations of the Effect pro- 

 duced by the Diminution of Light upon the Animal and 

 Vegetable Kingdoms." By EDWARD JOSEPH LOWE, Esq., 

 F.R.A.S., F.G.S., F.L.S., F.Z.S. &c. Communicated by 

 THOMAS BELL, Esq., P.L.S. Received April 1, 1858. 



[Abstract.] 



By the author's request, observations were made at 9 A.M., 1 1 

 A.M., and from noon every fifteen minutes up to 2 h 16 m , at 3 P.M., 



