Experiments and Discoveries. *6fl 
these points of no action in the same plane P And, if so, is that 
plane parallel or oblique to the horizon ? A series of experi- 
ments directed to this inquiry demonstrated, that the points 
were all in the same plane ; and that this plane formed with the 
horizon an angle equal to the complement of the dip, descending 
from the north towards south. That this ought to be the case 
when the needle had its natural dipping position, might easily 
have been foreseen ; because, then, the iron would be symmetri- 
cally situated with respect to the two poles of the needle ; but 
that it should still be the same with the horizontal needle, was a 
fact as novel to the author, as it was important in all his subse- 
quent pursuits. Having traced this circle on his iron-ball, and 
assuming the direction of the dipping needle as a principal axis 
to the same, its extremities forming the poles, he was imme- 
diately in possession of an ideal magnetic sphere, by which to 
indicate the relative position of the iron and compass in all his 
future inquiries ; and to this happy idea he is doubtless in- 
debted for the remarkable success with which his experiments 
have been attended. 
The nature and properties of -this ideal sphere, and the faci- 
lities it affords in all magnetical computations, will be more rea- 
dily comprehended by referring to Fig. 1. PL II., in which O is 
supposed to represent an iron-ball, and AAA a supposititious 
sphere circumscribing it, and within which its influence is active ; 
SCNQ' being the magnetic meridian. The line NS in the plane 
SENW, denotes the natural direction of the dipping-needle in 
these latitudes where its inclination to the horizon is about 70°. 
Now, conceiving QEQ'W to represent a circle or plane passing 
through the centre of the ball, and perpendicular to the axis NS, 
it will be the plane of no attraction , or the magnetic equator ; 
which, as we have seen, has this remarkable property, that if lines 
be drawn in it, (as for example, the lines OC, OC', OC", & c.), and 
a compass be placed any where in those lines, or, in short, in 
any point of the plane QEQ'W, it will be uninfluenced by the 
iron-ball, and preserve its natural magnetic direction. But, 
as soon as the compass is removed out of this plane, the needle 
is found to deviate from its original bearing; its south end 
being drawn towards the ball, when the needle is below the 
plane, and its north end when it is above ; and in every case the 
