N. D. C. Hodges—Method of Determining the Dip. 145 
Art. XVIL—A method of Determining the Dip; by N. D. C. 
Hopaes. 
THE magnetic polarity of a bar of soft iron is greatest when 
the bar lies in the line of the dip. This position of maximum 
intensity might be tested for by a small needle hung near one 
of the poles. This or similar ways have been used. The objec- 
tions are that the rate of change in the polarity is small as the 
bar approaches the position sought, and the testing needle takes 
a less and less sensitive position, since the farther it is turned 
from the meridian the greater becomes the movement of the 
force of the earth upon it tending to bring it back. If, instead 
of one bar, two bars joined at right angles at a point near their 
ends be used, these difficulties may be avoided. When sucha 
compound bar is placed so that the two branches make equal 
angles with the line of dip, the effect on one of them is to 
make the lower end a north pole and its upper end a south, on 
the other the lower a south and upper a north. Supposing the 
will move to correspond. To eliminate the effect of any per- 
manent magnetism in the iron, four readings may be taken; first 
