594 Mr. 0. V, Raman on the Curvature Method 



deduced and a determined ; and 



1 



Further, by means of the ruling on the reseau plate, the 

 difference of level between the vertices of the two curves can 

 be measured. This gives the pressure corresponding to the 

 observed curvature. 



In practice, it was found that the curvature of the larger 

 meniscus could not altogether be neglected. It amounted 

 to from 2 to 4 per cent, of the curvature of the smaller. 



This could be measured and allowed for. If — is the 



1 P 



curvature of the smaller and ^ that of the larger meniscus, 



then 



-(H)- 



(tali. 

 \P ^V 



h being the difference of level between the vertices. 



The liquid used in the experiments was clean distilled 

 water. Precautions were taken that in transferring the 

 liquid into the apparatus no contamination occurred. That 

 the surface whose tension was measured was free from 

 greasy contamination was ensured by allowing the water to 

 run down from the small tube for some time. The surface 

 of the drop that was finally left hanging was, therefore, an 

 absolutely fresh one, and any oily film originally on the 

 surface would have been reduced in thickness to a very great 

 extent. The parallelism of the beam used to photograph the 

 drop was tested by a telescope adjusted for infinity. To have 

 the photograph as sharp as possible, the plate was held only 

 3 cms. behind the apparatus. It was found that it was 

 necessary to adjust the wide tube so that it might be approxi- 

 mately vertical. If not, there was reason to think that the 

 iwo principal curvatures at the highest point of the large 

 meniscus would not be equal. This was really the weakest 

 point in the whole work. The writer hopes to repeat the 

 work with a tube so wide that the curvature of the meniscus 

 : above it can entirely be neglected. 



As an illustration of the method, I give a table of the 

 measurements made on one of the plates (see PI. XV.). 



