L42 J. K. Burba nk — Experiment on Surf ace Tension, etc. 



from the previous reasoning one might expect the viscosity of the 

 til in to destroy the rebound, but it is probable that while much 

 of it is destroyed in this way, yet the velocity of the drop and 

 its slight difference in density from the kerosene, make this 

 rebound a maximum. This is an extremely good illustration 

 of the tendency of a liquid to form in drops ; if the alcohol be 

 run in in a fine stream it breaks up into numberless drops, and the 

 surfaces of these drops are seen to be in rotational motion ; some- 

 times several of these drops crowd together and fall as a single 

 mass. The next trial was of olive oil in a mixture of alcohol 

 and water having a slightly greater density than that of the 

 oil itself; no rebound was observed, the velocity being very 

 small, and the flattening of the drop at impact very pronounced ; 

 this observation bears out the reasoning in regard to the action 

 of the kerosene after the surface of the water has been contami- 

 nated by the first few drops. 



It should be noted that the velocity of a solid sphere falling 

 in a liquid of uniform density becomes constant after a very 

 short interval of time ; this has been proved by Allen * and 

 others, and of course the same would apply to a solid sphere if 

 rising; except for the rotational motion it would doubtless 

 apply with similar accuracy to the motion of liquid drops in a 

 fluid of different density. In case a solid sphere is used of nearly 

 the same density as the liquid, a slight change in tempera- 

 ture will made a great difference in velocity of rise, and also 

 in rebounding effect. 



Conclusion. — As has been shown by Stokes, to whom refer- 

 ence is made in Allen's paper cited above, there is a certain criti- 

 cal velocity for a sphere moving in a mass of fluid; for veloci- 

 ties above this value, eddying motion is a disturbing factor in 

 the mathematical calculations, for velocities less than the 

 "critical" the mathematical equations hold. From these con- 

 siderations we might expect that for each sphere there would be 

 a certain "critical" velocity whicli would depend on the dif- 

 ference in density between the liquid and the sphere, on the 

 nature of the surface of the sphere, and on the surface tension 

 and superficial viscosity of the liquid film ; when this particu- 

 lar velocity is attained we would then have maximum force of 

 rebound. 



Physical Laboratory, 

 Univ. of Maine, Orono, Maine. 



* Motion of a Sphere in a Viscous Fluid, H. S. Allen, Phil. Mag., 1, 1900. 



