590 
ON THE POSITION OF THE SOUTH MAGNETIC POLE. 
by magnetic action will become a channel 
for an electric current; and whilst the 
whole circuit is metallic, the velocity of 
that current would be considerably greater 
than if any, even a small part of the circuit 
were of worse conducting materials : and if 
the current were suddenly transferred from 
a channel of the former character to one of 
the latter, by any contrivance whatever, it 
would meet a resistance on entering the new 
channel, which the momentum it had pre- 
viously required would have to overcome ; 
and a sudden disturbance of the electric 
fluid, previously at rest, would take place, 
and a violent rush of the current would as 
suddenly follow. 
It is in this manner that shocks and 
sparks are produced by magnetic electric 
machines, where the current, previously in 
rapid motion, is suddenly transferred to a 
new channel of inferior conducting charac- 
ter ; and all the fluid in the revolving coil 
rushes through a person properly situated 
for the new route, and who experiences the 
electric shock, or else through a thin stra- 
tum of air at an interruption in the metallic 
circuit where the spark is produced. 
These, then, are some of the effects of 
electric currents, or of the momentum of 
the electric fluid in a state of motion, after 
the exciting cause is entirely cut off. The 
shock thus produced may very conveniently 
be compared to the blow given by Mont* 
golfier’s hydraulic ram. Electro -momenta 
may be produced by any mode of excita- 
tion whatever, and the effects will be pro- 
portional to the velocity and quantity of the 
electric fluid first put into motion ; and the 
length of the original channel is also to be 
taken into account. If then electro-mo- 
menta, capable of producing violent shocks 
and vivid sparks, can be produced by a few 
hundreds of feet of thin copper wire, what 
is it that might not be expected from the 
electro-momenta of nature, arising from 
currents of many miles in extent, kept in 
motion either by heat, saline solutions, or by 
other causes, amongst the metalline strata 
below the surface of the earth ? A sudden 
disruption in the circuit would insure the 
blow, and an earthquake might be the result. 
— Philosophical Magazine, 1836. 
ON THE POSITION OF THE SOUTH 
MAGNETIC POLE. 
By Edward Rudge, Esq,., F.R.S., S. A., 
L.S. and H.S * 
The experiments detailed by Captain 
James Clark Ross, R.N. , &c., which led to 
• Read before the Royal Society, Feb. 19, 
18^5 ; and now communicated by the Author. 
the important discovery of the north magne- 
tic pole, and which are published in the Phi- 
losophical Transactions for the year 1834, 
suggested to me as an object of interesting 
inquiry, whether any similar affection of the 
horizontal magnetic needle had ever been 
noticed by any former navigator of the south- 
ern hemisphere , from which an approach to 
the magnetic pole could be surmised. 
No such appearances seem to have been 
observed by Anson, or any one after him ; 
but prior to his circumnavigation of the 
globe, Captain Abel Tasman, who was ap- 
pointed for the discovery of southern 
countries by direction of the Dutch East 
India Company, sailed from Batavia with 
two vessels on the l4th of August 1642, in 
his account of the voyage, gives the follow- 
ing particulars of an observation made on the 
22nd of November of the same year, when, 
by a prior and subsequent observation of 
November the l5th and 24th, he was in 
about latitude dSsilS., and longitude from 
Paris 160«. 
“The needle was in continual motion 
without resting upon any of the ei^ht points 
of the compass,” which he says, “led him to 
conjecture that there were some mines of 
loadstone on that spot.” 
Tasman’s Journal, written in Low Dutch, 
is now an extremely rare book : a translation 
of it is given in Dr. Hooke’s Philosophical 
Tracts, p. 179, for the year 1682; in Nar- 
borough’s and in Correal’s Collections of 
Voyages ; and also by Harris, who gives a 
new translation of it in the second edition of 
his Collection of Voyages, where, although 
he notices Dr. Halley’s theory of the magne- 
tic poles, which was published in 1683, he 
does not seem to suspect that Tasman’s ob- 
servation of this very remarkable affection of 
the magnetic needle was made in the imme- 
diate vicinity of the south magnetic pole, at 
that period in that particular situation, as- 
certained by the horizontal needle only ; 
the dipping-needle, invented by Norman in 
1681, being then unknown. Dr. Halley was 
of opinion that the north magnetic pole was 
not far from Baffin’s Bay, and that the south 
magnetic pole was in the Indian Ocean, 
south-west from New Zealand ; whether he 
ha I availed himself of the observation made 
by Tasman in forming this opinion, does not 
appear. Euler places the north magnetic 
pole for the year 1757 in latitude 76^^ north, 
and longitude 96® west from Teneriffe ; and 
the south magnetic pole in latitude 58^ south, 
and longitude 158^ west from Teneriffe. 
It has been ascertained by observation, 
that the magnetic poles were on the meridian 
of the poles of the earth at London in the 
year 1657, being fifteen years after Tasman’s 
observations, and that it reached its utmost 
degree of variation west in the year 1818, 
when it became stationary at 24° 26' west, 
and has since in respect of London been re- 
trograding towards the east, completing one 
quarter of the circle round the poles of the 
earth in 16! years at the rate of 11 or 12 
minutes of a degree in a year ; so that, pre- 
suming Tasman was on the south magnetic 
