240 Br. Thipson on the Variations of Densiti/ [May 26, 



unknown, or mistaken ; and the relationship, by structure or by imitation, 

 of the species and varieties is dwelt upon. For the description of the 

 better-known Foraminifera, the memoir refers to the works of Williamson 

 and Carpenter. 



The authors enumerate 109 specific and varietal forms, most of which 

 receive descriptive comment, and all of which are figured in five plates 

 (two for the North Atlantic and three for the Arctic Foraminifera) with 

 upwards of 340 figures. 



The relationships of the Lagence are specially treated of. Uvigerina, 

 Globigerina, and especially some of the Rotalince {Flanorhulina, Biscor- 

 bina, Rotalia, Fulvinulina) and Polystomella (including Nonionina) are 

 among those which are well represented in the fauna under description, 

 and have received much attention in the memoir. 



The Society then adjourned over the Whitsuntide Recess to Thursday, 

 May 26. 



May 26, 1864. 

 Major-General SABINE, President, in the Chair. 



The following communications were read : — 



I. " Note on the Variations of Density produced by Heat in Mineral 

 Substances.'' By Dr. T. L. Phipson, F.C.S., &c. Communi- 

 cated by Professor Tyndall. Received April 16, 1864. 



That any mineral substance, whether crystallized or not, should diminish 

 in density by the action of heat might be looked upon as a natural con- 

 sequence of dilatation being produced in every case and becoming per- 

 manent. Such diminution of density occurs with idocrase, Labradorite, 

 felspar, quartz, amphibole, pyroxene, peridote, Samarskite, porcelain, and 

 glass. But Gadolinite, zircons, and yellow obsidians augment in density 

 from the same cause. This again may be explained by assuming that 

 under the influence of a powerful heat these substances undergo some per- 

 manent molecular change. But in this Note I have to show that this mole- 

 cular change is not permanent but intermittent, at least as regards the 

 species I have examined, and probably with all the others. Such researches, 

 while tending to elucidate certain points of chemical geology, may likewise 

 add something to our present knowledge of the modes of action of heat. 



My experiments were undertaken to prove an interesting fact announced 

 formerly by Magnus, namely, that specimens of idocrase after fusion had 

 diminished considerably in density without undergoing any change of com- 

 position : before fusion their specific gravity ranged from 3*349 to 3'45, 

 and after fusion only 2-93 to 2-945. Having lately received specimens of 

 this and other minerals brought from Vesuvius in January last by my friend 

 Henry Rutter, Esq., I determined upon repeating this experiment of 



