228 HISTORY OF MAGNETISM. 



the King of Oude, at Lucknow. At all these distant stations tht 

 same plan was followed out, by observations strictly simultaneous, 

 made according to the same methods, with the same instrumental 

 means. Such a scheme, combining world-wide extent with the single- 

 ness of action of an individual mind, is hitherto without parallel. 



At first, the British stations were established for three years only ; 

 but it was thought advisable to extend this period three years longer, 

 to end in 1845. And when the termination of that period arrived, a 

 discussion was held among the magneticians themselves, whether it 

 was better to continue the observations still, or to examine and com- 

 pare the vast mass of observations already collected, so as to see to 

 what results and improvements of methods they pointed. This ques- 

 tion was argued at the meeting of the British Association at Cam- 

 bridge in that year ; and the conference ended in the rnao-neticians 



O / O 



requesting to have the observations continued, at some of the observa- 

 tories for an indefinite period, at others, till the year 1848. In the 

 mean time the Antarctic expedition had brought back a rich store of 

 observations, fitted to disclose the magnetic condition of those regions 

 which it had explored. These were discussed, and their results exhi- 

 bited, in the Philoso2^hical Transactions for 1843, by Col. Sabine, 

 who had himself, at various periods, made magnetic observations in 

 the Arctic regions, and in several remote parts of the globe, and had 

 always been a zealous laborer in this fruitful field. The general mass 

 of the observations was placed under the management of Professor 

 Lloyd, of Dublin, who has enriched the science of magnetism with 

 several valuable instruments and methods, and who, along with Col. 

 Sabine, made a magnetic survey of the British Isles in 1835 and 

 1836. 



I do not dwell upon magnetic surveys of various countries made by 

 many excellent observers ; as MM. Quetelet, Forbes, Fox, Bache and 

 others. 



The facts observed at each station were, the intensify of the mag- 

 netic force ; the declination of the needle from the meridian, some- 

 times called the variation ; and its inclination to the horizon, the 

 dip ; or at least, some elements equivalent to these. The values of 

 these elements at any given time, if known, can be expressed by 

 charts of the earth's surface, on which are drawn the isodynamic, iso- 

 yonal, and isoclinal curves. The second of these kinds of charts con- 

 tain the "Halleian lines" spoken of in a previous page. Moreover 

 the magnetic elements at each place arc to be observed in such a 



