NOTES. hi 



0") p. 176. "The magnet draws iron as amber attracts the smallest grains 

 of mustard seed. It is as if a mysterious breath of air passed through both, 

 and communicated itself with the swiftness of an arrow." Such are the 

 expressions used by Kuopho, a Chinese writer of the beginning of the fourth 

 century, in a speech in praise of the magnet. (Klaproth, Lettre a M. A. de 

 Humboldt, sur 1'invention de la boussole, 1834, p. 125). 



( 163 ) p. 177. "The phenomena of periodical variations depend manifestly 

 on the action of solar heat, operating probably through the medium T)f thermo- 

 electric currents induced on the Earth's surface. Beyond this rude guess, 

 however, nothing is as yet known of the physical cause. It is even still a 

 matter of speculation whether the solar influence be a principal or only a 

 subordinate cause, in the phseuomena of terrestrial magnetism" (Observ. to 

 be made in the Antarctic Expedition, 1840, p. 35). 



( 164 ) p. 177. Barlow, in the Phil. Trans, for 1822, Part i. p. 117 ; Sir 

 David Brewster, Treatise on Magnetism, p. 129. The influence of heat in 

 diminishing the directive force of the magnetic needle had been taught in the 

 Chinese work, Ou-thsa-tsou, long before the time of Gilbert and Hooke, 

 (Klaproth, Lettre a M. A, de Humboldt, sur 1'invention de la boussole, 

 p. 96). 



O 63 ) p. 178. See the Memoir on Terrestrial Magnetism in the Quarterly 

 Review, 1840, Vol. Ixvi. pp. 271312. 



( l66 ) p. 178. Vv f hen the first proposal to establish a system of observatories* 

 forming a net-work of stations, all provided with similar instruments, was 

 made by myself, I could hardly entertain the hope that I should actually live 

 to see the time when, thanks to the united activity of excellent physicists and 

 astronomers, and especially to the munificent and persevering support of two 

 governments, the Russian and the British, both hemispheres should be covered 

 with magnetic observatories. In 1806 and 1807, my friend, M. Oltmanns, 

 and myself, frequently observed the march of the declination needle at Berlin, 

 for five or six days and nights consecutively, from hour to hour, and often 

 from half hour to half hour, particularly at the equinoxes and solstices. 1 

 was persuaded that continuous uninterrupted observations (olservatio per* 

 petua), during several days and nights, were preferable to detached observations 

 continued during an interval of many months. The apparatus employed was 

 Prony's magnetic telescope, placed in a glass case, and suspended by a thread 

 without torsion, by which angles of 7 or 8 seconds could be read on a finely- 

 divided scale, placed at a distance, and illuminated at night by a lamp. 

 Magnetic perturbations, or storms recurring sometimes at the same hours for 



