A method of determining the dip

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 objections 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 such a compound bar is placed so that the two branches make equal