298 TERRESTRIAL MAGNETISM.—MURPHY. 
pole revolves around the north pole of the earth from east to 
west in about this time.” 
The latter reasoning is rather vague in taking means of such 
extremes, and these extremes between points so close as London 
and Paris. The permanency of the compass in Jamaica since 
1660, says Sir John Herschel, is remarkable. He says :—Dur- 
ing the last century all surveys of property there have been con- 
ducted solely by the compass. There is very little magnetic 
variation. Humboldt says:—If we compare Ermen’s observa- 
tions in the southern part of the Atlantic Ocean where a faint 
zone (0.706) extends from Angola over the Island of St. Helena 
to the Brazilian coast, with the most recent investigations of the 
celebrated navigator, James Clark Ross, we shall find that on the 
surface of our planet the force increases almost in the relation 
of 1:3 towards the magnetic south pole where Victoria Land 
extends from Cape Crozier towards the volcano Erebus, which 
has been raised to an elevation of 12,600 feet above the ice. 
The intensity near the magnetic south pole is expressed by 2.052 
(the unit still employed being the intensity which he discovered 
on the magnetic equator in Northern Peru) Sabine found it was 
only 1.264 at the magnetic north pole near Melville Island 
(74° 27’ north lat.) while it is 1.803 at New York. 
All these different systems of magnetic Jines—variation, dip, 
and intensity—have not on the earth that symmetry and regu- 
larity which they would present around a steel bar; on the 
contrary, they are often bent, looped, and turned into devious 
paths, wherefore none can tell. The fact alone is well estab- 
lished, while theories fail to account satisfactorily for the earth 
being an irregular magnet. 
Now, on the earth, the pole nearest the geographical pole is 
commonly known as the north magnetic pole, and the end of 
the needle pointing to it is also spoken of as the north pole, 
whence repulsion, of necessity, would seem to result; but this is 
an unfortunate use of the terms that has grown up with us. The 
real state of the case is, that whichever of the two—the earth’s 
pole or that of the compass—-we agree to designate as north, 
the other, having magnetism of the opposite kind, must be called 
the south ; and hence attraction naturally takes place. 
