[THOMPSON] 



ADVANCE OF THE RIPPLE 



135 



a distinct ripple; in fact, it appears that the phenomenon is more 

 definite with the strong salt solutions than with tap water or vinegar 

 or sulphuric acid. 



In order to obtain a more accurate method of measuring the ad- 

 vance of the ripple, a photograph was taken as the ripple was passing 

 an intense source of light, as shown in Figs. 2 and 3. This source, 

 MM, is due to a mercury vapour arc in a Torricellian vacuum within 

 a quartz tube. It was extremely difficult to obtain negatives from 

 which prints might be obtained, yet from them the advance of the 

 ripple could be easily measured. 



Using the method just mentioned for measuring the advance of 

 the ripple, the relation between the velocity of the moving surface and 

 the advance of the ripple was studied for a strong solution of sodium 

 chloride (specific gravity 1 • 195). The results are tabulated below and 

 a graph (1) was plotted as in Fig. 6. For the same velocity, the ad- 

 vances varied by not more than one millimetre. An average of four 

 readings was used. The diameter and length of the tube used was 

 2 '20 and 80 cm. respectively. The selected point was 30 cm. above 

 the level of the liquid in the dish. 



Table III — Relation between the Advance of the Ripple and Velocity 

 OF THE Moving Surface for the Strong Salt Solution 



The previous experiment was repeated, using solutions of varying 

 specific gravities and also water. The results are given in Table IV 

 and graphs (2, 3, 4, 5 and 6, representing respectively five solutions of 

 specific gravities M95, M50, 1-100, 1-050 and 1^000) are plotted 

 as in Fig. 6. 



