I 



415 



Professor Forbes also mentioned tha objection recently taken by 

 M. Agassiz to this theory of the veined structure being due to the 

 different velocity of parallel portions of the ice, namely, that where 

 two glacier streamers unite, their structure remains separate and 

 distinct. Professor Forbes admits that it does so for a certain dis- 

 tance after union, but affirms, that, if the glacier bo long enough, 

 the structure always tends to consist of a single series of curves. 

 He shewed, by models formed by the union of two plastic streams, 

 that, in point of fact, such phenomena of united streams may be re- 

 produced, the double structure being very slowly worn out, in con- 

 sequence of the nearly uniform movement of the middle part of the 

 stream. 



Professor Forbes recapitulated the proofs that the glacier moves 

 as a plastic mass, the friction of whose parts is less than their fric- 

 tion upon the surface over which they tend to slide ; and he bases his 

 theory upon three classes of facts, which he ccnsidei'S that he has 

 demonstrated. 1. That the glacier moves like a stream, fastest at 

 the centre. 2. That its velocity is immediately governed by the 

 external temperature and the state of infiltration of the ice by water 

 at the time. 3. That the forms which its veined structure assumes 

 are those due to the movement of a semi-solid mass in the manner 

 supposed. 



The following Donations of Books to the Society's Library 

 were announced. 



Archives du Museum d'llistoire Naturelle, publiees par Ics Pro- 



fesseurs-Administrateurs de cet Etablissement. Tome ii. 



Liv. 3. — By the Editors. 

 Coniptes Rendus Ilebdomadaires des Seances de I'Academie des 



Sciences. Tome xv. Nos. 9-26, et Tome xvi. Nos. 1-7. 



— By the Academy. 

 Monthly Notices of the Astronomical Society of London. Vol. v. 



No. 28. — By the Society. 



Specimen de I'lmprimeric de Bachclier, Rue de Jardinet. — By M. 

 Bachelier. 



Henry Stephens, Escj was duly elected an Ordinary Fellow 

 of the Society. 



