80 



The Rev. H. Lloyd on the Results of Observations made at the 



8. If we calculate the values of A, corresponding to the even hours of Dublin 

 mean time, by means of the formula of Art. 5 and the numbers of Table II., 

 we obtain the following values, in which the positive numbers correspond to 

 easterly deviations of the north pole of the magnet, as before. 



Table III. Diurnal Variation of the Declination (calculated Values). 



These numbers, together with those of Table I., are projected in curves in 

 Plates I. and II. already referred to. Plate I. contains the curves of the six 

 months of the summer half-year, together with the mean of the six ; Plate II. 

 those of the six months of the winter half-year, and the mean. The scale is 

 one-tenth of an inch to a minute of arc. 



9. The hours o{ greatest and least declination are deduced from the genera] 



, . clA 

 equation, by making -r- 



; they are consequently given by the formula 



Si {Bi cos ix — Ai sin ix) — 0. 



Substituting for Ai and Bi their numerical values (Table II.), and solving the 

 resulting equations by approximation, we obtain the following results : 



