86 SCIENCE PROGRESS. 



remembered, a valuable series of "contributions" to terres- 

 trial magnetism by Sabine, and, coupled with every available 

 observation between the years 1818 to 1876, formed the 

 materials for the series of charts entitled " The Magnetic 

 Survey of the Globe " for the epoch 1842*5. Each map 

 gave normal lines of equal values of the Declination, In- 

 clination and Intensity. Although it may be said that from 

 the Arctic circle to the Antarctic, the direction of the lines 

 was efficiently given by observation, the lines within those 

 circles were largely taken from Gauss's computed lines 

 modified to agree with observation. 



Another difficulty in compiling these charts of Sabine's 

 with accuracy lay in the uncertain knowledge of the secular 

 change then available, and which had to be applied to 

 observations made so far apart in time. 



Sabine's charts are doubtless the best we have for the 

 epoch 1842*5, but in the light of the requirements of 

 modern science they leave much to be desired as regards 

 the Antarctic regions. The observations south of 6o° S. 

 were made entirely on board ships, where the errors of the 

 compass sometimes exceeded 50° due to the horizontal 

 forces in the ship, thus rendering accurate observations of 

 the Declination very uncertain and correction of the observed 

 Inclination very difficult ; besides which there are no 

 records of the ship's disturbing force in the vertical direc- 

 tion. 



Naval requirements, however, did not permit of any 

 delay in publishing magnetic charts affecting navigation, 

 for in 1846 the Hydrographer of the Admiralty requested 

 Sabine to provide charts of the Declination for the Atlantic 

 Oceans from 6o° N. to 6o° S. These were largely used until 

 Evans's chart of the Declination for the whole navigable 

 world was issued in 1858. 



The excellent work of Flinders already referred to, of 

 ascertaining from his knowledge of terrestrial magnetism 

 the chief cause of the deviation of the compass in wood- 

 built ships, and providing a corrector for those deviations, 

 had to be followed up on a much larger scale and with 

 more exact methods in the iron-built ship, which, in that 



