Page:Scientific Memoirs, Vol. 2 (1841).djvu/70

58 It has been already stated that exceptions sometimes occur on single days, when the difference between the forenoon and afternoon declinations may have the opposite sign. But such exceptions are rare; during the three years' observations only fourteen cases of the kind have occurred; or, on an average, one in 79 days. I give them in this place, together with the amount by which, on each occasion, the declination at 8, exceeded that at 1,

Of these fourteen exceptions, twelve, as might be expected, occur in the winter months, and only two in the summer months; the small regular action of the sun in the former being more easily exceeded by an anomalous movement than could be the case in regard to the far greater regular action in the summer months.

To try how far the secular variation might be recognised in the present observations, the monthly means of the first year have been compared with the corresponding ones of the second, and these with those of the third year. Among the forty-eight comparisons thus obtained (for the incomplete month of March, 1834, has been excluded from this as well as from all the other combinations), forty-seven give a decrease, and only one an increase, which is therefore characterised in the following table by the sign—.

Yearly Decrease of the Declination.