154 POPULAR LECTURES AND ADDRESSES. 



the data required for working out the spherical 

 harmonic analysis of terrestrial magnetism over 

 the whole earth. A recalculation of the harmonic 

 analysis for the altered state of terrestrial magnet- 

 ism of the present time has been undertaken by 

 Adams. He writes to me that he has " already 

 " begun some of the introductory work, so as to be 

 " ready when Sir Edward Sabine's Tables of the 

 "values of the Magnetic Elements deduced from 

 ''observation arc completed, at once to make use 

 " of them," and that he intends to take into account 

 terms of at least one order beyond those included 

 by Gauss. The form in which the requisite data 

 are to be presented to him is a magnetic Chart of 

 the whole surface of the globe. Materials from 

 scientific travellers of all nations, from our home 

 magnetic observatories, from the magnetic 

 observatories of St. Helena, the Cape, Van 

 Dicmcn's Land, and Toronto, and from the 

 scientific observatories of other countries have been 

 brought together by Sabine. Silently, clay after 

 day, night after night, for a quarter of a century he 

 has toiled with one constant assistant always by 



