The range was surveyed by Cuyler Adams, using a dip needle in 1895.
2.
Another important improvement to the instrument was developed in the 1830s by the Dublin Physicist Humphrey Lloyd, who devised a way of attaching a magnetic needle at right-angles to the dip needle in order to measure the intensity of force ( by seeing the extent to which the right-angle needle deflected the dip-needle ).
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