550 



April 17, 1845. 

 Sir JAMES CLARK ROSS, V.P., in the Chair. 



" Description of a Self-registering Thermometer." By Mr. Mans- 

 field Harrison. Communicated by James Alderson, M.D., F.R.S. 



The instrument here described is composed 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. 

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

 and Professor of Natural Philosophy in the University of Edin- 

 burgh. 



The author adduces some nevv' 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 

 nature and as to the laws they obey. Various quotations are given 

 from authors who have been struck with this analogy, and who have 

 pointed it out more or less circumstantially in the narratives of their 

 travels in the neighbourhood of Etna and Vesuvius ; to which the 

 author adds some of his own observations on the lava from these 

 mountains, which throw further light on the subject. 



