Surface Tension and Superficial Viscosity. 141 



cally the same ; no allowance could be made, however, for the 

 effect between the film and the paraffin in the last position. 



2. After noting the height to which the ball rose at first 

 impact, the ball was removed from the water so as to break 

 the film, then lowered in again to the same height as at impact 

 and allowed to fall. In no case was the distance fallen as great 

 as on rebound from the film. Both of these methods were 

 very rough, and only comparative measurements were taken. 



A wooden ball of 3 # 4 cms diameter, weighted in same way as 

 paraffin, was next tried ; the results were of the same nature 

 but not so strong owing to the capillary action of the film on 

 the slightly rough surface of the ball. With this ball it was 

 possible to get velocities sufficient to break the film but no 

 observations were taken in regard to this point. 



The paraffin ball was then tried in alcohol and similar results 

 to those in water were obtained. It was next tried in kerosene 

 oil but the clinging of a layer of oil prevented any positive 

 results. It was finally tried in a strong solution of soapy 

 water, which would have a film with great viscosity and small 

 tension ; a film of this kind should show a greater rebound 

 than pure water, other conditions being the same, because the 

 actual time interval of contact between the ball and film 

 would be greater than in pure water on account of less tension 

 of film ; this greater time interval would allow the eddies in 

 the wake of the ball more time to die out and thus less resist- 

 ance would be opposed to the rebound. Observation showed 

 that this reasoning was correct, the distance of rebound being 

 decidedly greater than from a surface of pure water. 



Liquid spheres rebounding from liquid surf aces. —Kerosene 

 of specific gravity ■ 78 was run into the bottom of a jar of 

 water about 40 cms deep, by means of a long tube ending in a U- 

 shaped capillary small enough so that the drops escaped at the 

 rate of 2 or 3 per second ; these drops would rise with consider- 

 able velocity and at the very first, while the surface of the 

 water was clean, many of them would rebound, but only through 

 about l/2 cm ; this small rebound is due partly to the difference, 

 in density between kerosene and water, but chiefly to the flat- 

 tening of the drop. After a few drops of kerosene have risen 

 to the surface none of the drops will rebound but the flattening 

 effect is more noticeable; this would also be explained by the 

 longer time interval of contact between drop and film ; the 

 shorter the interval of contact the more nearly the drop 

 behaves like a solid sphere, precisely similar to the effect of strik- 

 ing the surface of water with the hand. A jar containing a little 

 water was filled with kerosene, and alcohol of specific gravity 

 about *81 was run in from a pipette ; the rebound of the alcohol 

 from the film between the kerosene and water was very evident ; 



