[maass] 



MEASUREMENT OF SURFACE TENSION 



135 



The figure is not drawn to scale, the size of the stream and the 

 tube from which it flows being exaggerated as compared with the other 

 objects. The fîow of the stream was kept constant by allowing more 



Fig. 4. 



water to enter at A than would pass through the constriction at E. 

 The excess water was drawn ofif at B, a constant head being thus 

 maintained. The size of the stream would be fixed for different 

 experiments by varying the constriction in the outflow tube at E. 

 The stream fell into a square glass box G, partly filled with water, the 

 latter being kept at a constant level H by means of the syphon K. 

 After equilibrium had set in, the outflow per second was measured in 

 graduated jar M. From the surface of the water, waves travel up the 

 stream F, and these waves were stationary if the surface of the water 

 which the stream strikes was steady. This was best obtained by using 

 a wide syphon to draw off the outflow, as by this means the surface H 

 could be kept absolutely still. 



By means of the condensor O, a beam of parallel light is thrown 

 through the jet which is then photographed. Exposures of from 

 i to i\) second were employed. 



Parallel to the stream and close beside it was placed a glass 

 plate with co-ordinate lines (not shown in Fig. 4). These lines were 

 photographed with the jet. By measuring the distances on the 

 negative and the original between two lines the magnification is found. 

 Figures 5, 6 and 7 show three photographs obtained in this way. 



In Fig. 7 the stream was allowed to strike the convex surface 

 of a watch glass. It was found that the water did not run off con- 

 tinuously and the waves were not absolutely steady. This method 

 can, however, be employed to measure the surface tension of liquids 

 which cannot be obtained in large quantities. 



After the stream has been photographed the wave-lengths are 

 measured. In each stream there are three or four waves which admit 

 of accurate measurement; thus in Fig. 5 there are four such waves. 

 The measurement is made by placing the negative under a microscope 



