2 Prof. W. A. Norton on Terrestrial Magnetism. 
he was enabled to trace the magnetic equator, with peculiar ac- 
curacy, through an extent of 247° of longitude. In his paper 
on the magnetic equator, subsequently published, he announced 
that he had discovered that “the points of this great circle, or 
those where the magnetic intensity is a minimum, are also the 
warmest points of each meridian,” and thus that “ the thermal 
and magnetic equator are connected, as Sir David Brewster had 
already proved to be the case with the thermal and magnetic 
les ;” also, “ that in comparing the isothermal and isodynamic 
lines, he had found a remarkable analogy in their curvatures and 
particularly in the direction of their concavities, and convexities.” 
M. Kupffer, in certain memoirs read before the Russian Academy 
about the year 1829, attempted to establish that terrestrial mag- 
netism resides at the surface of the globe, and thence inferred the 
existence of a connection between the magnetic and thermal phe- 
nomena of the earth : conceiving that the intensity of the earth’s 
magnetism would vary directly or inversely as the temperature, 
according as it was of the nature of permanent or induced mag- 
netism. 
Several conjectures have been formed as to the nature of the 
connection between the temperature and magnetism of the earth. 
Dr. Traill has expressed the opinion that “the disturbance of the 
equilibrium of the temperature of our planet, by the continual 
action of the sun’s rays on its intertropical regions, and by the 
polar ices, must convert the earth into a vast thermo-magnetic ap- 
paratus.” Christie has suggested that “ difference of temperature 
may be the primary cause of the polarity of the earth, though its 
influences may be modified by other circumstances.” (CErsted 
conceives that the sun, by producing evaporation, deoxydation, 
cc., as well as by increasing the temperature, is the exciting 
eause of electrical currents, which perpetually traversing the 
earth’s surface in a direction nearly parallel to the equator, give 
to the earth “a constant magnetic polarity.” Perhaps the more 
generally received theory of the present day concerning the phys- 
ical nature of the earth’s magnetism, is that it consists of thermo- 
electric currents circulating at or near the earth’s surface, In 
duced by the heat of the sun. Prof. Barlow, who adopts this 
view, conceives that only one link is wanting to complete the ex- 
planation of terrestrial magnetism, viz. the discovery of the me- 
tallic thermo-magnetic apparatus. Brewster remarks upon this, 
that “if it could be shown that the action of solar heat is cape 
ble of developing magnetism in particles such as those whieh are 
known to constitute our globe, the great difficulty would be re 
moved.” 
In seeking for the explanation of the connection between the 
i thermal phenomena of the earth, philosophers seem 
hitherto to have regarded the heat as only modifying in some m- 
