232 THE LIFE OF JAMES 2). FORBES. [CHAP. 



of chains rather overdone. ... He considers that car- 

 bonated springs are, as a rule, higher in temperature 

 than others, and spoke of the large number of them 

 which are found in Nassau and in other countries, the 

 deeper valleys of which contain hot springs. ... He 

 also spoke of a theory of variations of atmospheric 

 pressure in summer and winter, depending on the fact 

 that the superior current will sooner find its way to the 

 surface of the earth in winter than in summer. . . . 



' In the afternoon I observed the dip of the magnetic 

 needle at Poppelsdorf, with very concordant results, and 

 afterwards called on Professor Gustav Bischoff, who 

 showed me the sheets of his work on the temperature of 

 the earth. He had made experiments on springs, with 

 a view to getting a law of decrease of temperature in 

 ascending ; but he was " bothered " by the influence of 

 the proper temperature of the different depths from 

 which they take their origin. He does not consider that 

 carbonated springs are, generally speaking, hotter than 

 others. ... He has also made experiments on the 

 cooling of spheres of melted basalt, having a diameter of 

 twenty-seven inches, and others of nine inches. He 

 tinds for thermometers at different depths in arithmetical 

 progression, the temperature increase geometrically, and 

 the velocity of cooling is as the diameter simply, and 

 refers to Newton's experiment, which it confirms, 

 and which seems curiously mangled in quotation by 

 Dulong and Petit. The specific gravity of glassy slag 

 is less than that of slowly cooled basalt. . . . Von Buch 

 came in as we were examining these. 



* Bischoff also took a piece of basalt, split in two, and 

 tied together with twine (the use of the two pieces was to 

 test the completeness of the fusion), fixed it in the axis 

 of a cylindrical mould, and poured molten iron round it. 

 This latter in cooling (according to him) expanded and 

 squeezed the basalt. Certainly, many dykes of basalt in 

 iron appeared, very prettily, but I doubt the squeezing, 

 especially from the large cavities left in the iron, a fact 

 which was also noticed by Von Buch : whether there 



