MAGNETIC OBSERVATIONS. . 69 



feeblest intensity (Sabine, in the Phil. Transact, for 1846, pt. 

 iii., p. 254 ; and in the Manual of Scient. Inquiry for the use 

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



1828-1829. The Voyage of Hansteen and Due: Magnetic 

 observations in European Russia, and in Eastern Siberia as 

 far as Irkutsk. 



1828-1830. Adolf Erman's voyage of circumnavigation, 

 v^^ith 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 reputa- 

 tion to this expedition, which was equipped at the expense 

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

 informed and skillful observer. See the General Declination 

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

 Committee relative 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 pavil- 

 ion specially erected for the purpose at l5erlin, and provided 

 with one of Gambey's compasses. Corresponding measure- 

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

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

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

 ations in reference to the variation and intensity of the hori- 

 zontal magnetic force till November, 1830 (Poggend.,^w7ia- 

 len, bd. xv., s. 318-336 ; bd. xix., s. 375-391, with 16 tab. ; 

 bd. XX., s. 545-555). 



1829-1834. The botanist David Douglas, who met liis 

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

 bull had previously been caught, made an admirable series of 

 observations on declination and intensity along the north- 

 west coast of America, and upon the Sandwich Islands as 

 far as the margin of the crater of Kiraueah (Sabine, Rep. of 

 the Meeting of the British Association at Liverp9ol, p. 27-32). 



« 



By absolute measurements we are not only enabled to compare numer- 

 ically 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 present epoch with that which may be found at 

 future periods." Sabine, in the Manual for the use of the British Navy, 

 1849, p. 17. 



