374 Aslfonomical and Nautical Collectiom. 



more, of equal magnitude, beginning with the year 1821 ; the 

 English computers having always neglected to attend to the 

 observation of Mr. Burckhardt, contained in a note at the 

 end of his Tables, that the Supplement of the node is to be 

 diminished by 7' whenever it is to be inserted in an Almanac. 

 It may, however, be remarked, that this omission can never 

 have a sensible effect in any computations, for which the mean 

 place of the node, as set down in the Almanac, is employed ; 

 and that both these misconceptions might have been easily 

 avoided, if the learned author of the tables had condescended 

 to give a single example, of the manner in which a computer is 

 to proceed, in employing every part of them. But it must be 

 confessed, that it is difficult for a real mathematician to be 

 aware of all the precautions, that are required, for avoiding the 

 occurrence of errors of this sort in the hands of mere me- 

 chanical labourers. 



V. The Force of Magnetism, compared with the Dip, Extracted 

 from Captain Sabine's Appendix to Captain Parhy's 

 Journal. 4to. London, 1821, p. cxxxviii. 



" Having detailed the Observations on the intensity of the 

 Magnetic Force, it may not be uninteresting briefly to examine, 

 how far the results are consistent with the ratio in which it was 

 expected that the magnetic force would be found to vary under 

 different dips of the needle. 



" In the Rules and Tables for clearing the Compass from 

 the regular Effect of the Ship's Attraction, printed in 1819 by 

 order of the Commissioners of Longitude, and published, with 

 some alterations and additions, in the Journal of the Royal In- 

 stitution for October, 1 820, the magnetic force in the direction 

 of the dipping needle is considered to vary, inversely, as the 

 square root of four diminished by three times the square of the 

 sine of the dip ; and the force acting on a needle limited to a 

 horizontal motion, inversely, as the square root of three increased 

 by the square of the secant of the dip. 



'* The Observations at Melville Island are entitled to principal 



