588 



the aggregate amounts of disturbance would differ but little, and 

 that 1861 would be the first year of medium, showing an aggregate 

 amount of disturbance considerably below 1858, 1859, and 1860. 

 This expectation has been realized ; and we have now before us the 

 prospect that the present year, 1862, will prove to be the second 

 year of medium, with an aggregate amount of disturbance nearly 

 resembling that in 1861, but a little less; and that 1863, 1864, 

 and 1865 will be years of minimum, differing little from each other 

 in the amount of disturbance, and all lower than the preceding years 

 1861 and 1862 on the one hand, or the succeeding years 1866 and 

 1867 on the other. Hence we see the importance of maintaining, 

 during the remaining portion of the decennial period, the photogra- 

 phic records of the Kew Observatory, with as little change as may 

 be practicable in the instruments and methods which have been 

 employed during the first portion. 



The Table which is printed in vol. x. of the Proceedings, page 627, 

 shows the aggregate values of the disturbances in 1858 and 1859 

 distributed into the several solar hours of their occurrence, and 

 distinguishing between the disturbances which produce westerly and 

 those which produce easterly deflections of the compass-needle. It 

 also exhibits the ratios of disturbance at the several hours to the mean 

 of the 24 hours taken as the unit. The subjoined Table contains the 

 same particulars for the/owr years, 1858 to 1861, inclusive. It has 

 of course a somewhat higher authority than the earlier table, inas- 

 much as ratios obtained from the records of four years are to be pre- 

 ferred to those derived from two years only. But the principal point 

 of interest in comparing them with each other is the evidence which 

 their correspondence affords, of the substantial truth of the two first 

 of the three general conclusions adverted to in the commencement of 

 the present communication, viz., the periodicity of the disturbances in 

 respect to the several hours of solar time, and the distinct character of 

 the laws which regulate the disturbances producing westerly deflec- 

 tions, and those producing easterly deflections. The principal features 

 of both classes of disturbance are the same, whether viewed in the 

 record of the two or of the four years. Regarded from either point 

 of view, both classes follow progressions manifestly dependent upon 

 the hours of solar time, the progressions of the westerly and those of 

 the easterly deflections being as manifestly governed by distinct and 



