978 



dal distributions, and expresses the magnetic force at any external 

 point, or at any internal point in an infinitely small crevass tangential 

 to the lines of magnetization, as the resultant of a certain distribution 

 of tangential magnetization in an infinitely thin shell, coinciding with 

 the surface, and occurred to the author as the analogue of a method 

 which he had long before found for expressing the force due to a 

 lamellar distribution. In this last-mentioned method, which is 

 confined to lamellar distributions, the force at any external point, or 

 at any interior point in an infinitely small crevass perpendicular to 

 the lines of magnetization, is expressed as the resultant of a certain 

 distribution of normal magnetization in an infinitely thin shell coin- 

 ciding with the surface. 



9. "Les Causes da Magnetisme terrestre prouvees.". Par M. Pierre 

 Beron. Communicated by John Lee, Esq., LL.D., F.R.S. &c. 



The author considers the elements of terrestrial magnetism to be, 

 that the force with which the magnetic needle maintains its position is 

 not everywhere the same, and that its declination and inclination vary 

 from one region to another. These elements, he states, undergo very 

 difilsrent modifications, which may be reduced to the following:— 



1. Variations with reference to the position of the sun to the south 

 or to the north of the equator; 2. diurnal variations in different 

 regions of the earth ; 3. disturbances which proceed from changes 

 of weather, and from volcanic irruptions, and those which are ob- 

 served during the appearance of the aurora borealis ; 4. secular 

 variations. 



Adopting the views which have long since been put forward, but 

 without adverting to the opinions of others who have preceded him 

 in the same path, the author refers all the phsenomena of terrestrial 

 magnetism to the action of thermo-electric currents, and states, that 

 as we know from climatology the regions of the earth which have 

 the most hetero-thermal seasons, we have data for determining the 

 intensity and direction of the thermo-electric currents in every region 

 of the globe. 



The hetero-thermal regions being marked by the isothermals of 

 the most hetero-thermal months, the author distributes the thermo- 

 electric currents into four magnetic systems, in each of which the 

 currents are directed towards the middle, marked by the culmina- 

 tion of the isothermals. He then endeavours to trace out the general 

 connexion between the thermo-electric currents which he assumes 

 and the magnetic phsenomena as observed in what he terms the 

 American, the Asiatic, the Australian, and the Gallipagos' magnetic 

 systems. 



The extraordinary disturbances in the direction of the needle, he 

 attributes to changes in the regular order of the distribution of solar 

 heat, which give rise to corresponding changes in the thermo-elec- 

 tric currents ; and the secular variation to the amelioration of cli- 

 mate arising from the culture of the soil in different regions of the 

 earth. 



The author concludes his memoir with the following remark :— . 



