Variation Phenomenon of Terrestrial Magnetism. 497 



When we consider that the intensity of the magnetization of 

 the great globe of the earth is quite comparable with that 

 which we produce with much difficulty in our steel magnets, 

 these immense changes in so large a body force us to conclude 

 that we are not yet acquainted with one of the most powerful 

 agents in nature, the scene of whose activity lies in those 

 inner depths of the earth, to the knowledge of which we have 

 so few means of access." The time is at hand for another 

 Halley, or another Gauss, to put new life into this most fasci- 

 nating subject and give birth to a new and more productive 

 terrestrial magnetism. 



Hornstein's discovery has been abundantly verified since, and 

 now we are to consider an attempt equally as bold as his, for 

 its author believed he had reache'd such results that he felt 

 able to declare himself thus, confidently : " From the various 

 movements of the declination and inclination needles, corre- 

 lated with each other in time, direction and amount, on dif- 

 ferent parts of the earth's surface, the theory of a fluid 

 interior may now be considered to be as firmly established as 

 the doctrine of the diurnal rotation of the earth on its axis." 

 If this be true more than one science has become the debtor to 

 terrestrial magnetism. 



The experiments upon which this bold declaration was based 

 were announced in a paper read before the Royal Society, 

 June 19, 1890, by Mr. Henry Wilde, F.R.S., entitled " On the 

 Causes of the Phenomena of Terrestrial Magnetism, and on 

 some Electro-Mechanism for exhibiting its Secular Changes in 

 its horizontal and vertical Components." This paper having 

 evidently been well received was followed six months later by 

 another, embodying further investigations, " On the Unsym- 

 metrical Distribution of Terrestrial Magnetism," and on June 

 11, 1891, still another was read "On the Influence of Temper- 

 ature upon the Magnetization of Iron and other Substances." 



These three papers have now been combined and the pam- 

 phlet printed in English, French and German. Owing to the 

 great promise they apparently hold forth and the interesting 

 physical questions involved, they are receiving marked attention 

 at the hands of terrestrial magnetists. In this country a brief 

 description was given it and the claims of the author were set 

 forth in the January number of the American Meteorological 

 Journal, but no attempt whether of verification or discussion 

 made. And on February 3d, 1892, appeared an editorial in 

 the N". Y. Tribune under the caption : " A Scientific Mystery 

 Unravelled." To the writer's knowledge no effort as yet has 

 been made to refute Mr. Wilde's theory. He, having in his 

 possession the means of instituting a comparison between fact 

 and theory and being familiar with the comprehensive investi- 



