631 



tions at Kew in immediate juxtaposition with the easterly at Hobar- 

 ton, and vice versa, as that obviously constitutes the just compari- 

 son. The Hobarton Ratios exhibit the relative prevalence of dis- 

 turbance at the several hours, derived from hourly observations con- 

 tinued for seven years and nine months, viz. from January 1, 1841 

 to September 30, 1848 ; a series unparalleled in duration at any other 

 of the Colonial Observatories, and which has borne admirably, as I 

 shall hope to have a future opportunity of explaining to the Society, 

 an unquestionable test of its substantial accuracy and fidelity. The 

 number of recorded hourly observations was 56,202, of which 7638 

 differed from their respective normals of the same month and hour 

 by an amount equalling or exceeding 2'* 13 of arc, and constituted 

 the body of separated observations from which the aggregate values 

 of disturbance at the different hours and their ratios have been 

 obtained. The proportion of disturbed observations thus separated, 

 to the whole body of observations, is about 1 in 7*35 ; differing very 

 little from the proportion already noticed as obtained at Kew by a 

 separating value of 3''3. The disturbing effects due to magnetic 

 storms are therefore somewhat greater at Kew than at Hobarton, 

 though some portion of the difference may be ascribed to the cir- 

 cumstance, that the terrestrial horizontal force, antagonistic to the 

 disturbing forces and tending to retain the magnet in its mean 

 position, is less at Kew than at Hobarton, in the proportion, approx- 

 imately, of 3-7 to 4- 5. 



