588 Royal Society, 



suppose the protoxide of iron to be combined with silica in 

 the form of silicate of iron, and this silicate scattered through 

 the crystal, it is obvious that the mineral, if pure, would be 

 an anhydrous silicate of alumina, having an atomic weight of 

 4-25. 



I have compared the specimens of bucholzite from America 

 with sillimanite, and find them to agree, excepting that the 

 bucholzite is not so pure as the sillimanite. The shape of the 

 crystals, the hardness and lustre, and the specific gravity agree 

 very nearly. 



I have never seen the ^droliie of Bournon and Chenevix, 

 but the descriptions and analysis correspond with those of 

 sillimanite. 



Henceforward the terms sillimanitei bucholzite and Jibrolite 

 may be dropt, and the species distinguished by the name of 

 silicate of alumina, which indicates the chemical constitution 

 of the mineral. 



LXXVIII. Proceedings of Learned Societies. 



ROYAL SOCIETY. 



[Continued from p. 452.] 



April 17, " T^ESCRIPTION of a Self-registering Thermometer." 



IS'l'S. -*-^ By Mr. Mansfield Harrison. Communicated by 

 James Alderson, ]M.D., F.R.S. 



The instrument here described is com}Dosed of two parallel bars, 

 the one of iron and the other of copper, united at their lower end, 

 and registering their differences of expansion by heat, by means of 

 a series of multiplying levers, carrying a pencil which is made to 

 press on paper wound round a cylinder moved by clock-work. 



" On the Viscous Theory of Glacier Motion. Part I. containing 

 Experiments on the Flow of Plastic Bodies, and Observations on the 

 Phenomena of Lava Streams." By James D. Forbes, Esq., F.R.S. 

 Lend, and Edin., Corresponding Member of the Institute of France, 

 and Professor of Natural Philosophy in the University of Edin- 

 burgh. 



The author adduces some new experiments in confirmation of his 

 theory of the nature and causes of the motion of glaciers, and which 

 present an analogy with the phenomena exhibited by the flow of 

 masses of semifluid or viscous matter contained in a narrow channel, 

 along which they move by the force of gravity ; and also with the 

 ripple marks on the surface of a stream of water when its course is 

 impeded by obstacles. These latter phenomena, he remarks, were 

 noticed and accurately described by Leonardo da Vinci. Analogies 

 of a still more striking nature are presented by the appearance of 

 streams of lava in their flow from volcanos and in the progress of 

 their descent, which illustrate a great number of the phenomena of 

 glacier motion, and corroborate the views of the author as to their 



