72 COSMOS. 



Ley's inclinatorium and oscillation needles supplied by Han- 

 steen. 



1831. Dunlop, Director of the Observatory of Paramatta, 

 Observations on a voyage to Australia (Phil. Transact, for 

 1840, pt. i, pp. 133140). 



1831. Faraday's induction-currents, whose theory has 

 been extended by Nobili and Antinori. The great discovery 

 of the development of light by magnets. 



1833 and 1839 are the two important epochs of the first 

 enunciation of the theoretical views of Gauss : (1) Intensitas 

 vis magneticse terrestris ad mensuram absolutam revocata, 

 1833 ; (p. 3 : " elementum tertium, intensitas, usque ad 

 tempora recentiora penitus neglectum mansit ") ; (2) the 

 immortal work on " the general theory of terrestrial mag- 

 netism " (see Results of the observations of the Magnetic 

 Association in the year 1838, edited by Gauss and Weber, 

 1839, pp. 157). 



1833. Observations of Barlow on the attraction of the 

 ship's iron, and the means of determining its deflecting 

 action on the compass. Investigation of electro- magnetic 

 currents in Terrellas. Isogonic atlases. Compare Barlow's 

 Essay on Magnetic Attraction, 1833, p. 89, with Poisson, 

 sur les deviations de la boussole produite par lefer des vais- 

 seaux in the Mem de Plnstitut, t. xvi, pp. 481 555 ; Airy, 

 in the Phil. Transact, for 1839, pt. i, p. 167 ; and for 1843, 

 pt. ii, p. 146 ; Sir James Boss, in the Phil. Transact, for 

 1849, pt. ii,pp. 177195). 



1833. Moser's methods of ascertaining the position and 

 force of the variable magnetic pole (Poggend., Annalen, Bd. 

 xxviii, s. 49296). 



1833. Christie on the Arctic observations of Captain Back. 

 Phil. Transact, for 1836, pt. ii. p. 377 (Compare also his 

 earlier and important treatise in the Phil. Transact, for 

 1825, pt. i. p. 23.) 



1834. Parrot's expedition to Ararat (Magnetismus, bd. ii, 

 s. 5364). 



1836. Major Estcourt, in the expedition of Colonel Ches- 

 ney on the Euphrates. A portion of the observations on 

 intensity were lost with the steamer Tigris, which is the 

 more to be regretted since we are entirely deficient in 

 accurate observations of this portion of the interior of 



