214 Mr. J. A. Wanklyn on the Movements of Cases. 



Hence in traversing a finite space its velocity would become 

 32 feet divided by infinity. It would therefore require an in- 

 finite time to traverse a finite space. A fortiori, in a second it 

 could not traverse a finite space. 



In like manner, any finite time being assigned, it can be shown 

 that in that time no finite space can be traversed. 



We are thus led to expect that carbonic acid should not 

 escape from a tube more rapidly when its mouth is turned down- 

 wards than when it is turned upwards. Nor does the fact, that 

 in the actual experiment the escape was more rapid in the former 

 position than in the latter, disprove the proposition; for in 

 the experiment there is a very great imperfection : viz., it is im- 

 possible to open a tube without creating a current. When a 

 current is set up, the gas moves en masse, and then it is quite 

 conceivable how gravitation can increase the movement • so that 

 the descent of a quarter of the gas in our experiments is no proof 

 that if the tube could be opened without disturbance there would 

 be a higher rate of egress than there is when simple diffusion 

 acts. 



In order to show experimentally that it is the upward cur- 

 rent of air which produces the retardation, the following expe- 

 riment was devised and executed. 



A tube 9 to 10 millimetres in diameter and 242 millimetres 

 long was provided with ground-glass plates, closing both top 

 and bottom. The top was fixed on with tallow, and the tube 

 used as though it consisted of a single piece. It was filled 

 with mercury and inverted in the mercurial trough, when it 

 proved to be tight. Carbonic acid was then introduced in the 

 usual way. The tube charged with that gas was then closed 

 with the other ground-glass plate and removed from the trough. 

 The. top was taken off. The bottom was then removed and 

 replaced in five seconds. The top was then put on, and the 

 tube taken back to the trough, and its gas passed into a 

 graduated tube and examined. It consisted of almost pure air : 

 91*111 vols, left 90*665 vols, not capable of absorption by 

 potash. 



This shows clearly that, however we may account for the mode 

 of action of the upward current of air, it is the upward current 

 which produces the remarkable retardation forming the subject 

 of this paper. 



Here it may be well to mention that a trial was made to 

 ascertain the extent of movement produced by simple diffusion. 

 The tube employed in the six first experiments was filled with 

 carbonic acid and exposed, mouth opening upwards, for five 

 seconds. 



Only about 3 per cent, of carbonic acid had left the tube, 



