XXXVI NOTES. 



her the diurnal variation scarcely reaches two minutes. Although Bombay is still 

 8 from the magnetic equator, the regularity of the turning hours is already 

 hard to recognise. Wherever in nature different kinds of disturbing causes act 

 in recurring, but wholly or partially unknown periods, then, inasmuch as the 

 disturbances often either counteract or unequally reinforce each other, the regu- 

 lating laws long remain concealed from us. 



( 16 ) p. 131. See the proofs in my Examen crit. de 1'Hist. de la Ge'ogr. t. 

 iii. p. 34 37. The oldest statement of any particular amount of declination 

 was by Keutsungchy, a writer of the beginning of the twelfth century, and was 

 E. S. (Klaproth's Lettre sur 1'Invention de k Boussole, p. 68.) 



( 161 ) p. 131. On the ancient intercourse of the Chinese with Java, according 

 to the accounts of Fahian in the Fo-kue-ki, see Wilhelm v. Humboldt, " Ueber 

 die Kawi-Sprache," Bd. i. S. 16. 



( 162 ) p. 131. Phil. Trans, for 1793, p> 340349; for 1798, p. 397. The 

 result which Macdonald derives from his observations at Fort Marlborough 

 (situated above the town of Bencoolen, in Sumatra, 3 47' S. lat.), according 

 to which the easterly elongation increases from 19 h to 5 h , does not seem 

 to me to be quite warranted. After the hour of noon, the first observation 

 ordinarily taken was either at 3 h , 4 h , or 5 U ; and some detached observations, 

 occasionally made at other hours, render it probable that in Sumatra, as at Ho- 

 barton, the turning hour from east to west was as early as 2 h . We have twenty- 

 three months of declination observed by Macdonald (from June 1794, to June 

 1796), and it appears from them that at all seasons the east declination increased 

 from 19^ h to noon, by a continuous movement of the needle from W. to E. We do 

 not find in these observations any trace of the type of the phenomena of the 

 northern hemisphere (Toronto movements), which prevails from May to Septem- 

 ber at Singapore ; although Fort Marlborough is almost under the same meridian 

 as Singapore, and only 5 4' of latitude from it; the Earth's equator, however, 

 passing between the two places. 



( Ii53 ) p. 132. Sabine, Magn. Obs. made at Hobarton, vol. i. (1841 and 1842) 

 p. xxxv. p. 2 and 148; vol. ii. (1843 1845) p. iii. xxxv. and 172344. 

 Compare also Sabine, Obs. made at St. Helena; the same in the Phil. Trans, for 

 1847, Pt. I. p. 55, PI. IV. and Phil. Trans, for 1851, Pt. II. p. 636, PL XXVII. 



( 164 ) p. 133. Kosmos, Bd. i. S. 190 (English edition, p. 172). 



( 165 ) p. 134. Sabine, Observations made at the Magn. and Meteor. Observa- 

 tory at St. Helena in 18401845, vol. i. p. 30, and the same in the Phil. 

 Trans, for 1847, Pt. I. p. 51 56. PI. III. The regularity of the opposition in 

 the two parts of the year, May to September following the type of the middle 

 latitudes of the northern hemisphere, and October to February the type of the 



