592 Mr. C. V. Raman on the Curvature Method 



point D. If T is the surface-tension, then 



2T 

 9 



9< 



CD, 



<r being the density of the liquid, since CD is the head at the 

 point D. This is true, provided that the surface of the drop 

 is one of revolution about CD. p can be determined by 

 measuring the coordinates x and ?/, of points on the curve 

 ADB. 



= Lt 



t 



riff. 2. 



In practice, it is quite sufficient to make the measurements 

 of x and y close to the vertex for two or more values of x. 



The value of the ratio —^ at different points close to the vertex 



varies only very slightly, and any variation shown can be 

 corrected for, by calculating the value of the ratio for the 

 point x = from the observed values of the ratio. The reason 



2 



why the ratio 4~ varies very little can easily be seen. As 



we go up along the surface from the vertex D the head 

 diminishes, and therefore also the sum of the principal 

 curvatures. The section of the 

 surface is therefore nearer being 

 a parabola than a circle, for the 

 sum of the principal curvatures of 

 a paraboloid of revolution dimi- 

 nishes as we recede from the vertex. 



The measurements of x and y 

 were not made on the drop, but, 

 adopting a more accurate and con- 

 venient method, on a photograph 

 of the surface. The apparatus de- 

 signed for the purpose is shown in 

 fig. 2. 



A tube 2 cms. diameter is con- 

 nected up with a tube 6 mms. dia- 

 meter by caoutchouc tubing. The 

 arrangement shown in the figure 

 is filled up with the liquid. The 

 small tube can easily be adjusted 



so that the liquid bulges out of both tubes, the concavity 

 being in opposite directions in the two. A plumb-line 



