626 



different parts of the globe, as well as its comparative magnitude in 

 relation to the more regular solar-diurnal variation ; hut it must be 

 a constant quantity throughout at one and the same station, or it 

 will not truly show the relative proportion of disturbance in different 

 years and different months. 



The strength of the Kew establishment being insufficient for 

 the complete work of a magnetic observatory, the tabulation of 

 the hourly directions from the photographic records has been per- 

 formed by the non-commissioned officers of the Royal Artillery, 

 employed under my direction at Woolwich, where this work has been 

 superintended by Mr. John Magrath, the principal clerk, as have 

 been also the several reductions and calculations, which have been 

 made on the same plan as those of the Colonial Observatories. 



In the scale on which the changes of direction of the declination- 

 magnet are recorded in the Kew photographs, one inch of space is 

 equivalent to 22' '04 of arc. On a general view and consideration of 

 the photographs during 1858 and 1859, 0'15 inch, or 3''31 of 

 arc appeared to be a suitable amount for the separating value to be 

 adopted at that station ; consequently every tabulated value which 

 differed 3'*31 or more, either in excess or defect from the -final nor- 

 mal of the same month and hour, has been regarded as one of the 

 larger disturbances, and separated accordingly. The number of dis- 

 turbed observations in the two years was 2424 (viz. 1211 in 1858, 

 and 1213 in 1859), being between one-seventh and one-eighth of the 

 whole body of hourly directions tabulated from the photographs, of 

 which the number was 17,319. The aggregate valne of disturbance 

 in the 24 24 observations, was 14,901 minutes of arc ; of which 7207 

 minutes were deflections of the north end of the magnet to the west, 

 and 7694 to the east ; the easterly deflections thus having a slight 

 preponderance. The number of the disturbed observations, as well 

 as their aggregate values, approximated very closely in each of the 

 two years, 1859 being very slightly in excess. The decennial period 

 of the magnetic storms, indicated by the observations at the British 

 Colonial Observatories between 1840 and 1850, had led to the antici- 

 pation that the next epoch of maximum of the cycle might take place 

 in the years 1858-1859. The nearly equal proportions in which the 

 numbers and aggregate values of the larger disturbances took place 

 in 1858 and 1859 are so far in accordance with this view. Should 



