( 4 11 ) 
might have occafioned the Earth to tremble. Nor can 
we this Way account for that remarkable Particular atten- 
ding thefe Lights, of being always feen on the Northfide 
of the Horizon, and never to the South. 
Wherefore laying afide all hopes of being able to ex- 
plain thefe Things by the ordinary Vapours or Exhalati- 
ons of the Earth or Waters, we are forced to have recourfe 
to other forts of Effluvia of a much more fubtile Nature, 
and which perhaps may feem mere adapted to bring about 
thofe wonderful and furprizingly quick Motions we have 
feen. Such are the Magnet leal Effluvia, whofe Atoms free- 
ly permeate the Pores of the mod folid Bodies, meeting 
with no Obftacle from the Interpofition of Glafs or Mar- 
ble or even Gold it felf. Thefe by a perpetual Efflux do, 
fome of them, arife from the Parts near the Poles of the 
Magnet, whilft others of the like Kind of Atoms, but 
with a contrary Tendency, enter in at the fame Parts of 
the Stone, through which they freely pals j and by a 
kind of Circulation furround it on all Sides, as with an 
Atmofphere, to the Diftance of fome Diameters of the 
Body. This thing des Cartes has endeavoured to explain 
( Princip . Philofoph- Lib 1 V.) by the Hypothecs of the Cir- 
culation ofeertain skrewed or (Iriate Particles , adapted to 
the Pores they are to enter. 
But without enquiring how fufficient the Cartefian 
Hypothecs may be for anfwering the feveral Phenomena 
of the Magnet : that the Fad may be the better compre- 
hended we {hall endeavour to exhibit the manner of the 
Circulation of the Atoms concerned therein, as they are 
expofed to view, by placing the Poles of a Terrella or 
Spherical Magnet on a Plane, as the Globe on the Hori- 
zon of a Right Sphere : Then firewing fine Steel dull or 
Filings very thin on the Plain all round it, the Particles of 
Steel, upon a continued gentle knocking on the un« 
dgrfideof the Plain, will by degrees conform themfelves 
