Page:A Voyage of Discovery and Research in the Southern and Antarctic Regions Vol 2.djvu/45

1841 have been supposed, we find the value of α to be almost identical with the result of the former experiments at Gillingham. From this accordance in the value of the constant, in dips which differ so greatly as from 69 N. to 70 S., we should infer the probability first, that the local attraction of the Erebus was due to induced magnetism alone, the influence of any portions of iron, which, in the strict sense of the term, were permanently magnetic, being insensible; and secondly, that no material change affecting the standard compass had taken place in the distribution of the iron. These inferences are by no means inconsistent with the supposition above suggested, that some portions of her iron might be of a quality intermediate between that of perfectly soft iron, which undergoes instantaneous change, and that of iron which acquires permanent magnetism, and that such portions should be liable, in regard to their magnetic condition, to be more or less in arrear of the ship's magnetic position. I abstain from entering further into this question at present, because a fitter opportunity of doing so will be afforded when the whole of the observations of the expedition shall be collected, including those which have to be made at Rio de Janeiro on the return from the high latitudes of the south, and in England, after passing through the low magnetic latitudes of the equatorial region. Should it prove that the induced magnetism of a ship due to any particular dip requires time for its full development, more or