XXX11 NOTES. 



always employed has been described by me in detail in my Asie Centrale, p. 

 465 467. A mean result with each needle consists of sixteen readings. In 

 estimating the probable value of determinations of such small quantities, it is 

 important to consider the details of observation. 



( 146 ) p. 123. Kosmos, Bd. i. S. 417 (English edition, Note 125). 



( 147 ) p. 123. Humboldt, Voyage aux Regions e'quinox. t. i. p. 515 517. 



( 148 ) p. 125. Erman, Reise urn die Erde,Bd. iL S. 180. 



( 149 ) p. 125. Kosmos, Bd. iv. S. 53 (English edition, p. 55). Petrus Pere- 

 grini wrote to a friend that, in 1269, he had found the variation in Italy 5 

 east. 



( 15 ) p. 126. Humboldt, Examen crit. de 1'Hist, de la Ge'ogr. t. iii. p. 29, 36, 

 38 and 44 51. Although Herrera (Dec.i. p. 23) says that Columbus had re- 

 marked that the magnetic variation (declination) is not the same in the day and 

 at night, yet this statement by no means justifies us in attributing to the great 

 discoverer a knowledge of the diurnal variation of the declination. From the 

 genuine journal of Columbus, in his Voyages published by Navarrete, we learn 

 from the part belonging to the 17th and 30th of September 1492, that he re- 

 ferred such changes to an " unequal movement of the pole-star and the pointers," 

 called by him watchers or guards (guardas). (Examen crit. de 1'Hist. de la 

 Ge'ogr. t. iii. p. 5659.) 



( 151 ) p. 126. Kosmos, Bd. iv. S. 60, Anm. 66 ; and S. 70, Anm. 72 

 (English edition, Note 66; and Note 72). The oldest printed observations in 

 London are those of Graham, in the Phil. Trans, for 1724, 1725, vo). xxxiii. 

 p. 96 107. (An Account of Observations made of the Horizontal Needle, 

 at London, 1722 1723, by Mr. George Graham.) He said that the change 

 in the declination depended " neither upon heat, nor cold, dry, or moist air." 

 " The variation is greatest between 12 and 4 in the afternoon, and least at 6 

 or 7 in the evening." These are not, indeed, the true turning hours. 



( 152 ) p. 127. This is shown by numerous observations ; by those of George 

 Fuss and Kowanko, at the observatory belonging to the Greek convent in Pekin ; 

 Anikin at Nertchinsk, and Riddell at Toronto in Canada (all places having 

 west declination) ; also by observations made by Kupffer and Simonoff, at Ka- 

 san ; by Wrangel at Sitka, on the north-west coast of America, notwithstanding 

 the frequent auroral disturbances ; by Gilliss at Washington ; Boussingault at 

 Marmato, in South America ; and by Duperrey at Payta, on the coast of Peru 

 (all places having east declination). The mean declination was : at Pekin 

 (Dec. 1831), 2 15' 42" W. (Poggend. Ann. Bd. xxxiv. S. 54); at Ner- 

 tchinsk (Sept. 1832), 4 7' 44" W. (Poggend. Ann. Bd. xxxiv.- S. 61) ; at To- 

 ronto (Nov. 1847), 1 33' W. (Compare Observ. at the Magn. and Met. Observa- 



