553 
of Edinburgh, Session 1833-84. 
8c* Since 28a and Sc* are supposed to be small compared with 
the height 2b, these shells may be treated as electromagnetic strips. 
The two strips we are considering, being on opposite sides of the 
origin, will produce deviating forces with opposite signs. Hence if 
the numerical magnitudes of the forces they cause are equal, they 
will produce no deviating effect on the magnetometer. 
ISTow it is evident, if such a magnetic strip be placed due east or 
due west of the magnetometer with its plane at right angles to the 
magnetic meridian, the deviating force due to it will be zero. But 
if its position be changed along the magnetic meridian, without any 
rotation, the deviating force will increase, pass a maximum, and 
again become insensible when the strip is carried to a very great 
See note, \\ 552. 
