M. KupfFer on Iso-geothermal Lines. 259 



Tsity of its magnetism will be the inverse of its temperature ;. 

 or it receives its influence from without, and is only like a 

 piece of soft iron to which the presence of a distant body com- 

 municates magnetism, and then the intensity of its magnetism 

 will increase with its temperature. Though the first of these 

 hypotheses has been hitherto generally adopted, yet the second 

 acquires some probability by the discovery of the magnetic in- 

 fluence of the solar rays, (See this No. page 225,) and of the 

 known relation between the diurnal variations of the dechna- 

 tion of the needle, and the course of the sun. 



If we consider the globe as a warm mass highly susceptible 

 of magnetism, whose surface has an almost uniform tempera- 

 ture, and which is rendered magnetic by the action of a dis- 

 tant celestial body, it is evident that its magnetism will be dis- 

 tributed in a manner perfectly regular, and that the lines of 

 equal inclination will coincide with those of equal intensity. 

 But if the surface becomes by degrees unequally heated, the 

 lines of equal intensity will be modified, and will in some 

 points separate from the lines of equal inclination. If one of 

 these last lines passes through several points in which the tem- 

 perature of the ground is the same, the intensity of magnetism 

 in these different points will also be the same ; but in all 

 points where the temperature of the ground is higher or lower,, 

 the intensity, according to our hypothesis, will be stronger or 

 weaker. This indeed appears to be the case, and if future 

 observations agree with those already made, we may regard 

 this circumstance as a powerful demonstration of the hypo- 

 thesis in question. 



In the magnetic chart of Hansteen, drawn in 1825, we see 

 f*^ that the lines of equal inclination and equal intensity are sen- 

 ' sibly parallel in Scotland, but that farther east, in Norway 

 and in Sweden, they both bend towards the north and cut 

 the first. Besides, on the same line of equal inclination, the 

 intensity is weaker to the east than to the west, and it is the 

 same with the temperature of the ground. Thus, for ex- 

 ample, the inclination is nearly the same at Edinburgh and at 

 Stockholm. But in the first of these towns the intensity is as 

 1.400, and the temperature of the ground T, whilst in the 

 second the intensity is as 1.886, and the tcmperatufe of the 



