MAGNETIC OBSERVATIONS. 69 



the points of feeblest intensity (Sabine, in the PJiil. Transact, 

 for 1846, pt. iii, p. 254, and in the Manual of Sclent. Inquiry 

 for the use of the British Navy, 1849, p. 17). 



1828 1829. The voyage of Hansteen and Due : Magne- 

 tic observations in European Russia and in Eastern Siberia 

 as far as Irkutsk. 



1828 1830. Adolf Erman's voyage of circumnavigation, 

 with his journey through Northern Asia, and his passage 

 across both oceans, in the Russian frigate Krotkoi. The 

 identity of the instruments employed, the uniformity of the 

 methods and the exactness of the astronomical determina- 

 tions of position will impart a permanent scientific repiita- 

 tion to this expedition, which was equipped at the expense 

 of a private individual, and conducted by a thoroughly well- 

 informed and skilful observer. See the general declination 

 Chart, based upon Erman's observations in the Report of the 

 Committee relat. to the Arctic Expedition, 1840, pi. 3. 



1828 1829. Humboldt's continuation of the observations 

 begun in 1800 and 1807, at the time of the solstices and 

 equinoxes regarding horary declination and the epochs of 

 extraordinary perturbations, carried on in a magnetic pavi- 

 lion specially erected for the purpose at Berlin, and provided 

 with one of Gambey's compasses. Corresponding measure- 

 ments were made at St. Petersburgh, Nikolajew, and in the 

 mines of Freiberg, by Professor Reich, 227 feet below the 

 surface of the soil. Dove and Riess continued these observa- 

 tions in reference to the variation and intensity of the 

 horizontal magnetic force till November 1830 (Poggend. 

 Annalen. Bd. xv, s. 318 336; Bd. xix, s. 375391, with 

 16 tab. ; Bd. xx, s. 545555). 



18291834. The botanist David Douglas, who met his 

 death in Owhyhee, by falling into a trap in which a wild 

 bull had previously been caught, made an admirable series of 



de Humboldt's original station in South America has been inferred to 

 be 1.372 to 1.000. This is the origin of the number 1.372, which has 

 been generally employed by British observers. By absolute measure- 

 ments we are not only enabled to compare numerically with one 

 another the results of experiments made in the most distant parts of 

 the globe, with apparatus not previously compared, but we also furnish 

 the means of comparing hereafter the intensity which exists at the pre- 

 sent epoch, with that which may be found at f uture periods." S&bine, 

 in the Manual for the use of the British Navy, 1849, p. 17. 



