Page:A Voyage of Discovery and Research in the Southern and Antarctic Regions Vol 1.djvu/181

] moderate weather, to determine the three magnetic elements with even more precision on board our ships than they are susceptible of on shore, on account of the unknown and indeterminable amount of local attraction; and even in the heaviest gales, after a little practice with his instrument, they may be observed with sufficient exactness to afford very useful and important information. Throughout the whole distance of between three and four thousand miles, from Kerguelen Island to Van Diemen Land, we could not have derived a single satisfactory result with the instruments in common use; and this portion of the ocean, at least, must for the present have remained a blank upon our charts. But, with Mr. Fox's apparatus, the dip and intensity observations were accomplished in an almost uninterrupted series of daily experiments.

By reference to the annexed table, the progressive increase of intensity, after leaving Kerguelen Island, and the points at which we successively crossed the isodynamic lines of 1.5, 1.6, 1.7, &c., until, on the sixth of August, in lat. 46° 44′ S., and long. 128° 26′ E., we found it to attain its greatest amount in this parallel of latitude, being there 2.034, and thence again as gradually diminishing to 1.824 at Van Diemen Land. The weather did not admit of our attempting to determine the actual position of the focus of maximum intensity, which, from our observations, we considered to be far to the southward of the course