294 TERRESTRIAL MAGNETISM.—MURPHY. 
and southern inclination poles, and must not be confounded with 
the intensity poles presently to be mentioned. As we leave 
either inclination pole, the dipping needle leaves its vertical po- 
sition and gradually approaches the horizontal direction, until, 
along a curve lying midway between the two poles, the needle 
becomes exactly horizontal. This curve is called the magnetic 
inclination equator. 
. Lastly, as to the intensity. If we noticed in every part of the 
earth’s surface the number of times the needle vibrated through 
its position of rest in a given interval, we should find that along 
acurve lving near to, but not absolutely coincident with the 
inclination equator, the intensity has a minimum value. This 
curve is called the intensity equator. Leaving it towards the 
north or south, we should find the intensity gradually increasing. 
We should not, however, find this increase guiding us to an 
intensity pole either north or south, but we should recognize two 
magnetic intensity poles in each hemisphere. 
Now, in considering the various relations here presented, it is 
important that we should decide which property of the magnetic 
needle should be adopted as our guide or receive our chief atten- 
tion, 
General Sabine considers that intensity is the primary quality 
of the magnet in all such inquiries as we are at present concerned 
with. Professor Proctor considers that if we were to select one 
or the other of these elements as our special guide it must clearly. 
be the inclination, because he says the declination has compara- 
tively narrow limits of range, which the inclination varies from 
0 to 90. 
If a properly balanced magnet could be suspended or supported 
so as to be free to take up any position, it would be found at 
London at the present time, that it would finally rest in a posi- 
tion making an angle of about 67 degrees, with the horizontal ; 
also that the vertical plane passing through the magnet would 
make an angle of about 18 degrees with that of the meridian, 
the magnetic deviation being to the west of the true astronomical 
or geographical north and to the east of south. Such is the dip 
and declination given at the Royal Observatory for the first of 
i ian i i 
