On the Friction between Water and 4ir. 441 



April 6, 1876. 



Dr. J. D ALTON HOOKER, C.B., President, in the Chair. 



The Presents received were laid on the table, and thanks ordered for 

 them. 



The following Papers were read : — 



I. "Experiments on the Friction between Water and Air." By 

 Dr. Ritter von Lang. Communicated by N. Story Maske- 

 lyne, F.R.S., Keeper of the Mineral Department, British 

 Museum. Received February 28, 1876. 



(Abstract.) 



The method adopted for estimating the mutual friction of water and 

 air consisted in connecting a glass tube of 8 centims. in length and 072 

 internal diameter with the pipes which supply Vienna with water at a 

 pressure of four atmospheres. Arrangements for securing a vertical 

 position for the tube ensure a perfectly continuous jet, devoid of any 

 broken surface ; and a glass tube surrounding this jet, with its axis coin- 

 ciding with that of the jet, acts as an aspirator into and along which air is 

 drawn through a lateral feeding-tube. The amount of this indrawn air 

 corresponding to the fall of a given amount of water was determined by 

 observing the rate at which a film of soap was borne along the feeding- 

 tube ; and the velocity of the water causing the indraught was calculated 

 from the diameter of the water column and the quantity of water dis- 

 charged along it in a given time ; but after having once determined 

 the form of the slightly conical water column, the amount of water dis- 

 charged was the only datum required for the calculation. 



The influence of a greater or less section of the air feeding-tube on 

 the volume of the aspirated air was carefully determined, while also the 

 absence of any appreciable retardation due to the soap film was 

 established. 



Neglecting the slightly conical character of the surface of the water 

 column, and assuming (as the result of experiments in which the motion 

 of a smoke cloud was observed) that the movement of the air was 

 throughout in lines parallel to the axis of the tube along which it flowed, 

 and showing that the pressure does not vary along the length of the tube, 

 the author proceeds to discuss the hydrodynamic equations expressing 

 the conditions of the problem (the motion of the air being uniform and 

 independent of time), and represents the volume of air A passing through 

 the tube in a second as : — 



vol. xxiv. 2 E 



