TERRESTRIAL MAGNETISM.—MURPHY. 297 
On the western side of the Atlantic a line of no variation, as 
it is called, is marked on the Admiralty chart, which I place 
before you. It leaves Dutch Guiana, crosses the meridian of 60 
west from Greenwich, crosses the islands of St. Lucia and Porto 
Rico of the Antilles, runs Kast of San Domingo and San Salvador, 
of the Bahama Islands, touches the coast. of South Carolina at 
Long Bay, crosses the western shores of Lake Erie and the 
narrows between Lake Huron and Lake Michigan, follows the 
eastern shores of Lake Superior and touches Hudson Bay at 
West Pens, and after running through western waters of Hudson 
Bay passes through Pistol Bay and Farther Hope Island in 
Chesterfield Inlet. 
From these facts of observation, Professor Proctor seemed to 
favor the theory that at some time near the year 1657 the 
northern magnetic pole must have been on the meridian of 
Greenwich, or that the magnetic pole must have been directly 
between England and the real pole of the earth, or somewhere 
beyond the real pole; and as before 1657 the declination was 
easterly, whereas afterwards it was westerly, hence the magnetic 
pole must have travelled from east to west round the north pole 
of the earth, and he further says that from these observations 
we can learn something about the rate at which the magnetic 
pole is travelling. For he says :— 
“Supposing the magnetic needle in the meridian of London in 
1657, and Ross’s estimate of the place of the magnetic pole to 
be approximately correct, giving (in round figures) 95° west of 
Greenwich for the longitude of the magnetic pole in 1883, we 
get a period of revolution of 
~ X (1883-1657) years. 
= “x 176 years = 667 years about. 
“And combining Ross’s estimate with Paris epoch we get a 
period of 
+ X (1833-1663) years. 
= <- (* 170) years = 644 years about. 
“The mean of these values is about 655 years; and I think 
that there is good reason in believing that the northern magnetic 
