456 



LIBUT.-GENEEAL SABINE ON TEEBESTKIAL MAGNETISM. 



Column 5 contains the deviations computed with these constants, employing for that 

 purpose the Table in pages 352, 353 of the same Number of the Contributions ; and 

 column G shows tlie differences between the deviations so computed for the dip of — 53°, 

 and the mean deviations observed at Port Louis, where the dip was —52° 20', and at 

 Simon's Bay, where it was —53° 26'. The differences are all well within the limits of 

 errors of observation, and may justly be deemed insignificant. Employing the same 

 coefficients, the deviations were computed corresponding successively to dips of —56°, 

 — 59°, —62°, and —65°, comprehending the whole range encountered in the third year's 

 survey ; and a Table was formed by interpolation for the intermediate degrees, which has 

 been employed in correcting the Table of the declinations observed on board the 'Erebus' 

 between Port Louis in August 1842, and the Cape of Good Hope in April 1843. 



Table I. — ' Erebus.' Deviations of the Declination at Port Louis and Simon's Bay. 



2. In the ' Terror.' — A precisely similar process has been pursued in computing the 

 corrections to be applied for the influence of the ship's iron upon the observations of 

 the declination in the 'Terror' in this portion of the survey, commencing at Port Louis 

 in August 1842, and terminating at Simon's Bay, Cape of Good Hope, in April 1843. 



The deviations on the thirty-two points observed at Port Louis in August 1843, have 

 been already printed in a Table in No. VI. of these Contributions (Philosophical Trans- 

 actions, 1844, Art. VII. p. 89); and those observed at Simon's Bay in April 1843 are 

 now printed for the first time in page 457; their mean results are shown in the subjoined 

 Table, No. II. The constants B, C, D, and E in the equations, by which the delations 

 in dips of other amounts may be derived, have been obtained in the manner already 

 described in the case of the ' Erebus ;' their values are 



B=-2°37'; C=-0°20'; D=+0°17'; E=+0°04'. 



