498 L. A. Bauer — Wilde's Explication of the Secular 



gations of the Coast and Geodetic Survey undertook an 

 examination of Mr. Wilde's paper with the result of being- 

 forced to reach a conclusion somewhat at. variance with the 

 favorable comments already noted. 



Wilde's attempt may be classified as a twofold one : (1.) He 

 seeks to account for and reproduce those great changes in the 

 earth's magnetism taking place with the lapse of time, termed 

 its secular variation. Thus at London, about the } T ear 1657, 

 the magnetic needle pointed exactly north and south. It then 

 marched westward until about the year 1818 when it pointed 

 21° 38 ; to the west of north. After remaining stationary for 

 a few years, it began to turn backward on its course and march 

 eastward, so that in 1890 it pointed but 17° 26' to the west. 



(2). He seeks to account for and reproduce the unsym- 

 metrical distribution of terrestrial magnetism as manifested 

 to day, by which there are at present three well-defined lines 

 in the northern hemisphere where the needle points truly 

 north while there are but two in the southern hemisphere. 



The time allotted will only permit me to make brief men- 

 tion of the second and third papers : and in regard to them it is 

 believed that Mr. Wilde has reached most interesting and 

 valuable results. The purpose of my paper, however, is to 

 consider the first part, viz : the secular variation of terrestrial 

 magnetism, and as time will not allow me to discuss all the 

 results reached by Wilde, I will select those stations' where he 

 has actually attempted to reproduce the secular variation and 

 upon which certain constants of his theory depend. These 

 stations are : London, Cape of Good Hope, and St. Helena. 

 I will further limit myself by discussing only the secular varia- 

 tion as manifested in their declinations, for only on them do 

 the constants referred to, depend. If we succeed in over- 

 throwing these three cases, we have overthrown Wilde's 

 theory . 



Let us see what his theory is. Perhaps we have met with 

 the germ of it before. To avoid the danger of giving a mis- 

 conception of it, I have thought it best to give his own words 

 as far as possible. 



" It is assumed that the ring of cosmical matter, from which 

 the earth was evolved, resolved itself into a spheroid of glow- 

 ing vapors, similar in constitution to those of the sun in its 

 present condition. 



From the experience we have of the cooling of bodies from 

 a state of vapor, and by the law of continuity, the outer por- 

 tions of the spheroid would, in the course of time pass from 

 the gaseous to the liquid, and thence to the solid condition. 

 As the specific gravity of the principal constituents of the ter- 

 restrial globe is less in the solid than in the liquid state, the 



