DIURNAL VARIATION, &:c. xlv 



did not apply to the irregular variation ; it was therefore supposed to be occasioned by some 

 subterraneous heat which was at times unequally diffused. The above account will be 

 sufficient to prove that the discovery of diurnal variation is not of a modern date, but 

 we may pass over the experiments that were made subsequently, since none of them 

 threw any light on the subject, until it attracted the attention of the late Captain 

 Flinders, to whom also the discovery of the deviation of the magnetic needle is due. 



On my voyage to the Arctic Regions in 1818, the phenomena of the magnet parti- 

 cularly attracted my attention, and although a paper has been published in the Trans- 

 actions of the Royal Society, by Captain E. Sabine, the observations therein given are 

 exclusively mine, that gentleman not having been even on board or present when they 

 were made, but copied out of my note-book to which he had access. In both the 

 editions of my narrative of that voyage, I have given, not only the observations them- 

 selves, and conclusions drawn from them, but rules for the correction for deviation, 

 which are so simple, that any master of a merchant ship can as easily correct his 

 course for the deviation peculiar to his ship as for the variation of the compass. Nor 

 have these rules been superseded ; for although Professor Barlow's ingenious plate 

 has been described as " triumphant," it is by no means infallible, as it must be 

 acknowledged that any alteration in the situation of the iron material on board the 

 ship must affect its accuracy, and it cannot again be rectified without a good opportu- 

 nity when the ship is at anchor ; while it is at any rate a piece of expensive lumber, for 

 which there is not the least necessity, if the easy rules I have given are put 

 in practice. 



During my late interesting voyage, I have not only had an opportunity of confirming 

 all my former observations, but of adding many important facts, which our actual 

 approach to the magnetic pole has put us in possession of. My first series of observa- 

 tions were made at Felix harbour, in lat. 69° 59', long. 92° west, where the variarion 

 was found to be 89° 45' west, and the dip 89° 55'. In order to carry on the observations 

 on diurnal variation, which had been begun to the westward by Sir John Franklin, 

 I was, by the liberality of Sir George Murray, then Colonial Secretary, fiimished with 

 several instruments which had been used by that scienrific and persevering officer, 

 among them the diurnal variation instrument constructed by Mr. Dolland, from whom 

 I received the necessary instructions to use it. This instrument has already been 

 described by Sir John Franklin, but its microscopes were since altered to make the arc 

 more conveniently read off by them. Nevertheless, it was some time before I could 

 use it to obtain any satisfactory result; my magnetic observatory was built entirely of 

 snow, 200 yards distant from any metallic substance, and marks were put up for 

 placing it in the true magnetic meridian. I soon found that this instrument, which had 



