Proceedings of the British Association. 375 
cluding three series of observations—the declination, inclination 
and intensity. Prof. Loomis* had extended his observations of 
inclination over great part of Ohio, Indiana, Illinois and Missouri. 
These, and numerous other observations and surveys in the States, 
would connect the northern British survey with the determina- 
tions of Capt. Barnett, of the Thunder, in the Gulf of Mexico. 
As to observations at sea, by Mr. Fox’s instrument, the inclina- 
tion and dip of the magnetic intensity might be measured with 
all the precision requisite for every use to which observations at 
sea could be turned, for the purpose of tracing out the isodynam- 
ic and other magnetic curves in portions of the globe covered by 
water. ‘To extend and facilitate the use of this valuable instru- 
ment, the set of instructions drawn up by Col. Sabine, had been 
printed by order of the Admiralty, as a general circular, with some 
statements of the mode of using it practised on board the Hrebus 
and Terror, and the hope was expressed that this method would 
be followed, not only in exploratory voyages, but by ships pursu- 
ing ordinary tracks, so as to furnish data for complete magnetic 
sea-charts. For these important observations, as well as the de- 
clination, it was necessary to eliminate the influence of the ship’s 
iron,—an evil increasing from the greater quantity of iron now 
used. After mentioning the observations of Capt. Belcher, of 
the Sulphur, on more than twenty islands in the Pacific Seas, 
which had arrived in England, and would be published, and the 
important results deduced from M. Erman’s journey in Siberia, 
the report noticed the subject of magnetic disturbances, respect- 
ing which Gauss remarked, that one of the results of this great 
British enterprise was that the existence and extension of these 
disturbances over the whole of the globe had been ascertained. 
As a physical fact, deeply connected with the general causes of 
terrestrial magnetism, this was indeed a result of the first magni- 
tude, and considering all the circumstances, how it was modified 
by distance and locality, was eminently calculated to lead to the- 
oretical truths. It distinguished what was local from what was 
general, and traced individual shocks from observatory to obser- 
vatory, and station to station, till they were so far enfeebled as 
Pee Ss ee 
* See Prof. Loomis’s paper on the Magnetic Dip and Variation in Bie United 
States: this Jour. Vol. 43, p. 93-116. Also his paper on the Magne 
at several places in the United States: Trans. Am. Phil. Soc. Vol. 8, pay p- 61. 
