Balance Magnetometer 1858

INAF – Rome Astronomical Observatory

The balance magnetometer, also known as Lloyd’s balance, is one of the two instruments left from the Collegio Romano Magnetic Observatory. In the second half of 19th century this type of instruments was used in many geomagnetic observatories, mainly for determining the Z vertical component of the terrestrial magnetic field. The instrument and the method for measuring with it, were invented by the Irish physicist Humphrey Lloyd (1800-1881) around 1842. The magnetometer was mounted on a horizontal pane, adjusted by a level. The steel magnetic bar, 30.5 cm long, suspended like a very delicate balance pole, rested on agate spheres by means of a triangular knife. In order to be protected from air currents and be thermally isolated, the bar was placed inside a box, together with a thermometer. In his publications, Secchi underlined the stability and the degree of quality obtained with this instrument. He also noted that the major drawbacks were due to the presence of insects that, not caring about scientific research, often would enter inside the balance and affect its mechanism. [a.a., m.f., f.p.]

Bibl.: Altamore & Ptitsyna 2012.