120 



" The azimuthal velocity derived from M. Foucault's the- 

 ory is expressed by the following equation : 



dA , .\ 



-r=Asm A, 

 at 



0) 



in which A denotes the azimuth measured from the north 

 towards the east; k the angular velocity of the earth, i. e. 15° 

 per hour ; and A the latitude of the place of observation. This 

 expression indicates a uniform angular velocity, and a time of 

 revolution equal 24 ft x cosec. of latitude, which for Dublin 

 would be about 29 ft 50 m . 



" The following Table, No. I., contains the mean results 

 of the six experiments, giving the azimuth measured from N. 

 to E., and the mean hourly motion, during the successive 

 hours of observation : 



Table I. 



Hour. 



Hourly Motion. 



Azimuth. 



No. of Ex- 

 periments. 



I. 



12-86° 



12-86° 



6 



II. 



11-90 



24-76 



6 



III. 



11-61 



36-37 



6 



IV. 



11-50 



47-87 



5 



V. 



11-72 



59-69 



5 



VI. 



10-82 



70-41 



4 



VII. 



9-85 



79-46 



4 



VIII. 



10-77 



90-23 



4 



IX. 



13-00 



103-30 



6 



X. 



11-47 



114-77 



6 



XI. 



13-94 



128-71 



4 



XII. 



15-99 



144-70 



4 



XIII. 



14-32 



15902 



4 



XIV. 



12-42 



171-44 



5 



XV. 



6-96 



178-40 



5 



XVI. 



16-97 



195-37 



4 



XVII. 



10-40 



205-77 



3 



XVIII. 



12-38 



218-15 



3 



XIX. 



11-01 



22916 



3 



XX. 



1215 



241-31 



2 



