364* Mr. Christie on the diurnal deviations of the 
the magnets are in the meridian, and their poles are placed 
towards those of the needle of the same name, zero will still 
continue the point of stable equilibrium , and i8o° of instable 
equilibrium , while the terrestrial forces are greater than those 
of the magnets ; but when the forces of the magnets are 
equal to the terrestrial forces, both these points become what 
may be termed points of indifferent equilibrium, since the 
needle is not retained in the one by forces acting from the 
centre towards the extremities, nor do any forces act from 
the extremities towards the centre in the other: the equi- 
librium, however, at zero still possesses one character of sta- 
bility, a tendency to return to it when disturbed, whilst that 
at i8o° has the character of instability, a tendency to recede 
from it, under the same circumstances. If the magnets be 
brought somewhat nearer, the forces which they exert on 
the ends of the needle will be greater than the terrestrial 
forces, and zero will therefore become a point of instable , and 
i8o° of stable equilibrium. It is besides evident, that the excess 
of the forces of the magnets above the terrestrial forces may 
be such, that they will be in equilibrio between zero and i8o° ; 
so that there will be a point of stable equilibrium between zero 
and the west, and zero and the east. Corresponding and oppo- 
site to these there will be two points of instable equilibrium ; 
one between i8o° and the east ; the other between i8o° and the 
west. There would therefore now be six points of equilibrium, 
alternately stable and instable. As the magnets are made to 
approach the needle, the two easterly points of equilibrium 
will approach each other, and also the two westerly ; and 
when they coincide at east and west, the four will become 
two points of indifferent equilibrium, the resultants of alLthe 
