20 



Prof. G. H. Darwin. 



[Nov. 22, 



In one part 7 ripples to 9 inches ; at another part 12 ripples to 



1 foot ; some tendency to break into the octave. The ripples only 

 extended an inch or two from the edge. 



More water was then poured in until it stood about lj inches 

 deep. 



5. Repetition of No. 4. 



There were 33 ripples in a half circumference (which is 22 inches) ; 

 the ripples were more regular than in No. 4, with not so much 

 tendency to break into the octave. 



6. Water 2J inches deep ; frequency 59 ; amplitude 3 or 4 inches. 

 43 ripples to the circumference (which is 44 inches), extending 



inwards 8 inches. 



Hereafter the amplitudes were marked by a pointer projecting 



3 inches from the edge of the bath. 



7. Water 2J inches ; frequency 75 ; amplitude 2 J inches. 



66 ripples to circumference, very regular, and extending inwards 



4 or 5 inches. 



8. Water 2J inches ; frequency 74 ; amplitude 3 inches. 



63 or 64 ripples, extending 6 or 7 inches ; broken in two or three 

 places . 



9. Water 2-J ; frequency 75 ; amplitude 4 inches. 

 53 ripples, extending 8 or 9 inches ; not so regular. 



10. Water 2J ; frequency 78 ; amplitude 5 inches. 

 47 ripples, extending 10 or 11 inches. 



11. Water 2 J ; frequency 75 ; amplitude 6 inches. 



Agitation violent ; all the coarser sand collected round the margin, 

 without ripple-mark for 4 inches inwards ; from 4 to 11 inches 

 inwards, rather irregular ripples about 37 to circumference ; the 

 usual flat centre. 



12. Water 2| ; frequency about 80 ; amplitude 7 inches. 



The water churned up the sand with violence ; margin the same as 

 No. 11 ; from 8 to 12 inches from margin rather irregular ripples, 

 about 34 to circumference. 



13. (Bad observation.) Water 2| ; frequency about 85 ; amplitude 

 about 1^ to 2 inches. 



80 ripples to circumference. 



14. (Bad observation.) Water 2J; frequency 57; amplitude 



2 inches. 



No ripples raised. 



An analysis of the observations marked 7 to 14 was made on the 

 hypothesis that the water remained still, when the bath oscillated 

 with a simple harmonic motion. I endeavoured to find whether X, 

 the wave-length of ripple (in inches) was directly proportional to v, 

 the maximum velocity of the water relatively to the bottom (in inches 

 per minute) during the oscillatory motion ; also the values of v Y and 



