Page:Scientific Memoirs, Vol. 2 (1841).djvu/67

Rh at the same hour. In order to be able to calculate more easily on the possibility of a long and continuous perseverance, by which alone labours of this kind can be of value, I have at first rather chosen a limited plan than attempted to combine too much at once. On this account only two observations are made daily; at eight in the forenoon, and one in the afternoon, according to mean time. These hours, which were most easily compatible with other duties, are also suitable ones, because in the regular course of the magnetic movements the position of the needle at 1, is never far from the maximum of declination, and during the greatest part of the year, the hour of minimum is not far from 8,  Observations at fixed hours of apparent solar time would, it is true, have been more in accordance with nature; but the much greater facility of an arrangement made according to mean time, renders it deserving of preference in this case, where the chief point is to secure persevering continuance in one and the same principle.

A regular register was commenced on the 1st of January, 1834; but the first two months and a half have been omitted in the following extract, because during that time it was frequently necessary to wind up the suspension-thread, whereby changes were produced in the torsion which were at first not sufficiently attended to. From the 17th of March a stronger suspension-thread was employed, consisting of 200 fibres, of which the point of no-torsion had been previously accurately determined; whenever changes were subsequently made in respect to the thread, or to any other circumstance connected with the elements of reduction, the necessary corrections, or modifications of those elements, have each time been applied. During the first months various sufficiently practised observers took part with me in the observations; but since the 1st of October, 1834, they have been regularly made by Dr. Goldschmidt, his place having been only occasionally supplied, when necessary, by other expert observers.

I have already communicated in the Göttingen Gelehrten Anzeigen, 1834, p. 1269, and 1835, p. 345, the monthly means deduced from these determinations up to January, 1835: they are now given for three entire years.