7 
Hints for thé Formation of a Theory of the Earth. = 25 
as M. Prevoilt *, two fluids, fufceptible of being combined 
- ywith, each other in fuch a manner that one of them alone is 
accumulated around the north pole of a magnet, while the 
other is accumulated around the fouth pole; and that all the 
. Magnetic phenomena may be explained by the eleétive at- 
tractions which thefe fluids exercife either upon each other 
or on iron t, 
3. It muft then be examined, whether the direGtion of the 
magnetic needle, and its inclination, depend on the fituation 
of a Jarge magnet enclofed in the bowels of the earth, as 
Halley fuppofes ; or on the action of one of thefe two mag- 
netic fluids towards one of the poles, and, perhaps, of the 
other fluid towards the oppofite pole, as M. Prevoft fuppofes. 
4. If we admit the hypothefis of a large magnet fulpended 
within the cavity of the earth, fhall we fuppofe, as the in- 
yentor of this hypothefis, that this magnet has four poles ? 
Or, fhall we endeavour to explain the whole, as that great 
geometer Euler has done, by a magnet having only two 
poles? Or, laftly, fhall we fuppofe, as Mr. Churchman, an 
American philofopher, has lately done, that the earth con- 
tains two magnetic poles, one at the north and the other at 
* De Vorigine des forces magnétiques, 8. Geneve 17838. 
4+ The celebrated Coulomb admits alfo two fluids, which compofe the 
magnetic fluid, and which exercife their aétion in the inverie ratio of the 
{quare of the diftance: but, in the theory of phenomena conncéied with 
the aétion of the globe, this philofopher fets out from certain faéts imme- 
diately given by obfervation; one of which it would be of importance to 
yerify in different points of the globe. This faét is, that the forces which 
 attra&t one of the poles of a magnetic needle freely fufpended towards the 
north, are equal to thofe which attraét the oppofire pole towards the fourth. 
Coulomb concludes that this equality exifts, becaufe a needle, weighed two 
different times, before and after it was magnetifed, was found exactly of 
the fame weight. 
C. Borda has found, by obfervations made firft at Breft, Cadiz, Tene- 
riffe, Goree on the coalt of Africa, and afterwards at Breft and Guada- 
loupe, that the intenfiry of the force exercifed by the globe on the mags 
netic needle, eftimated according to the number of efcillations made by 
the needle in a given time, was fenfibly the fame in thefe different places: 
This obfervation in other latitudes, efpecially on approaching the poles, 
might throw fome light on the theory of natural magnetifm,.—Nore of 
C. Wavy. : 
Wou. V. E the 
