TEEEESTRIAL MAGNETISM. 393 



tion.s of the great oceans, valuble not onh^ for needful uses in making 

 charts for the seaman, but also as a contribution to magnetic science. 



Prior to this expedition very little was known from observation of 

 the distribution of terrestrial magnetism in the central regions of the 

 north and south Pacific oceans, and Sabine's charts are consequently 

 defective there. 



Combining the ChallengermsigneticsLl results with those of all avail- 

 able observations made by others of Her Majesty's ships and by colo- 

 nial and foreign governments, 1 was enabled to compile the gharts of 

 the magnetic elements for the epoch of 1880, which were published in 

 the i-eport of the scientific results of H. M. S. Challenger. I will ven- 

 ture to say that these charts give a fairly accurate representation of 

 the normal distribution of the earth's magnetism between parallels of 

 70- north and 40° south. Be3^ond these limits, either northward or 

 southward, there is a degree of uncertainty about the value of the lines 

 of equal value, especially in the southern regions — an uncertaint}' 

 which we have reason to hope will be dissipated when we know the 

 full results obtained by Captain Scott and the gallant band he com- 

 mands, for as yet we have to be content with some eddies of the full 

 tide of his success. 



Until the Discovery was built the ChaUemjerw^ifi the last vessel spe- 

 cially selected with a view to obtaining magnetic observations at sea, 

 so that for several years past results obtained on land have been our 

 mainstay. Thus, elaborate magnetic surveys with fruitful results 

 have been carried out in recent years in the British Isles by Kiicker 

 and Thorpe. France, Germany, Holland, and some smaller districts 

 in Europe have also been carefully surveyed, and British India par- 

 tially so, b\' Messrs. Schlagintweit in 1857-58. The latter country is 

 being again magnetically surve3'ed under the auspices of the Indian 

 government. 



On the American continent the coast and geodetic survey of the vast 

 territories comprised in the United States, which has been so many 

 years in progress, has been accompanied by an extended magnetic sur- 

 ve}^ during the last fifty-two years, which is now under the able direc- 

 tion of Dr. L. A. Bauer. Resulting from this some excellent charts 

 of the magnetic declination in the United States have been published 

 from time to time, and the last, for the epoch 190"^, is based upon S,(M)U 

 observations. 



There are other contributions to terrestrial magnetism for positions 

 on various coasts from the surveying service of the royal navy, and 

 our ships of war are constantly assisting Avith their ([uota to the mag- 

 netic declination, or variation, as sailors prefer to call it; and wisel}^ 

 so, I trow, for have they not the declination of the sun and other 

 heavenly bodies constantly in use in the computation of their ship's 

 position? 



