Note 150 — Chapter XXII
Reading edition
The foci are all of different intensities; that in the South Atlantic, discovered by M. Erman, has the least intensity of the four, and the other in the southern hemisphere, discovered by Sir James Ross, has the greatest; taking 1 as the unit at the magnetic equator in Peru, their intensities are as 2·071 and 0·706. In the northern hemisphere the American focus is more intense than that in Siberia, which is moving from west to east, while the minor focus in the southern hemisphere is moving from east to west.