Mr. F. Clowes on a Glass Cell with Parallel Sides. 61 



mense collection of extinct animals may be accounted for without 

 having recourse to the somewhat improbable theory that a very 

 great and sudden change had taken place in the climate of that 

 region. 



I have seen at the mouth of Hayes River in America animals 

 frozen up as above described ; but as the latitude of this place is 

 only 57° north, the fixed ice usually wholly disappears before 

 the next winter sets in, and liberates the animals shut up in it ; 

 but when the rivers reach the sea, as some of those of Siberia 

 do, 1000 or 1200 miles further to the north, it may be fairly 

 assumed that a large part of this fixed ice, protected as i would 

 be by a layer of mud, might continue unthawed. 



IX. Glass Cell with Parallel Sides. 

 By F. Clowes, Esq., B.Sc, F.C.S.* 



THE following method has proved very convenient for making 

 a glass cell, which may be readily fitted up from ordinary 

 laboratory apparatus, and may also be rapidly taken to pieces 

 for the purpose of being cleansed. 



A piece of india-rubber tubing with stout walls, or, better, a 

 length of solid rubber, is placed Fig, \, 



in the form of a letter U be- " ^__^_^ 



tween two plates of glass, the [tf » V \ j j nfn 



ends of these plates being then j jj \ \ ~~7 y 



firmly held together by slipping [. ji ^5 gjj==g 5^. [L. 



over them stout india-rubber 



rings. A glass cell is thus obtained, the parallel faces of which 

 are formed by the glass plates, whilst its thickness, depth, and 

 length can be suitably varied by the stoutness and length of the 

 rubber tube and the shape which this tube is made to assume. 



With a glass cell of the size of an ordinary magic-lantern 

 slide (fig. 1), the difference in specific gravity between hot and 

 cold water f may be well shown upon the screen by a magic 

 lantern, the liquid admitted by a pipette being preferably tinged 

 by dissolving in it a crystal of potassium permanganate ; and 

 the convective currents occurring in the mass of a liquid may be 

 thrown upon the screen by passing a galvanic current through 

 a fine platinum wire stretched between two thick copper wires 

 beneath the surface of the liquid in the cell : these currents are 

 rendered much more evident by allowing the platinum wire to 

 be immersed in a stratum of potassium-permanganate solution 

 which has been cautiously introduced beneath the water by 

 means of a pipette dipping to the bottom of the cell. 



* Read before the Physical Society, May 23, 1874. Communicated by 

 the Society. 



t See Tyndall's 'Heat, a Mode of Motion,' pp. 173 and 174. 



