Frederick Guthrie on Stationary Liquid Waves. 385 



Number of recurrences 

 of same phase in 1'. 

 f 94 



A. \ 94 

 I 94 



rio9 



B. \ 109 



1109 



Taking* the troughs A and B, we have the following- compa- 

 rison : — 



Fig. 7. 



A.... 106-9 

 B. . . . 122-4 



71-6 

 83-5 



94 

 109 



§ 29. Compound motions. — The motion given to a glass of 

 water when the axis is made to describe a narrow cylinder and 

 then brought to rest, whereby a wave careers round the vessel, 

 is a modification of the mononodal. If the node of such a 

 system performs one complete revolution during the phase-life 

 of the mononodal wave, the crest reappears in the same place. 

 In the trough B, which held 300 millims. of water, in each of 

 three experiments the crest reappeared in the same place eighty- 

 four times in one minute. The travelling of the node, therefore, 

 makes no difference in the wave-rate. The motion of the sur- 

 face resembles that of a disk which is at right angles to an 

 axis when the axis describes a circular cone. 



If the water revolves on its axis in the trough, mononodal 

 undulations are carried round in a similar manner. 



The revolution of the water does not interfere with the period 

 of the binodal circular waves. Thus the water in A, being 300 

 millims. deep, was stirred round ; and while in rapid rotation, it 

 was impressed with the circular binodal wave-system. In each 

 of two minutes 107 waves were counted ; and the last minute 

 was immediately following the first. At the end of the expe- 

 periment the water was still circulating at the rate of 12° 

 per 1". 



§ 30. Oil on water. — The restraining effect of a layer of oil 

 Phil. Mag. S. 4. Vol. 50. No. 332. Nov. 1875. 2 C 



