286 



Proceedings of the Royal Irish Academy. 



6. 9th July, 1879. — Observed by Dr. Macalister and self, using 

 double readings with both indices : — 



n 



e 



Combination. 



7 







346''-750 



(0, 16) 



306-3 



1 



295 



875 



(0, 15) 



306-9 



2 



254 



375 



(0, 14) 



308-5 



3 



217 



500 



(0, 11) 



307-3 



4 



187 



625 



(0, 4) 



305-1 



5 



160 



625 



(0, 5) 



304-4 



6 



137 



375 



(0, 6) 



303-6 



7 



118 



500 



(0, 7) 



305-4 



8 



102 



500 



(0, 8) 



307-5 



9 



88 



000 



(5, 9) 



311-5 



10 



75 



750 



(5, 10) 



311-7 



11 



64 



825 



(5, 11) 



309-8 



12 



55 



250 



(0, 12) 



306-1 



13 



48 



125 



(0, 13) 



308-4 



14 



41 



375 



(10, 14) 



309-9 



15 



35 



125 



(10, 15) 



304-8 



16 



30 -000 



(10, 16) 



304-2 



Mean, . 



. . . 307"14 + 0-41 (mean proba 



jle en'or). 



The mean of this and the preceding Table is 



/ = 



306-335 



for amplitudes ranging up to 360°. The mean value of/ from all the- 

 experiments, is as follows : — 



1 



f'' 



Mean value of 1, 2, 3, 4, 308-50 



Mean value of 5, 305-53 



Mean value of 6, 307-14 



Mean of all, 307-057 



Prom the preceding value of / -we can determine the relation 

 between the slope of a water-surface and its velocity. "We have, for 

 the equation of motion of the surface, 



d'x . . .dx 



- = ^sm.-/-; 



(10) 



