Scale magnetometer

[ignoto], Roma, 1858
Wood, glass, marble and iron
45 X 25 x 20 cm
Museo of INAF-Astronomical Observatory of Rome, Monte Porzio Catone (Rome)

The scale magnetometer(also known as the Lloyd’s scale) shown here, is one of the two instruments of the magnetic Observatory of the Roman College (Figure 1a-B) surviving to this day. In the second half of the nineteenth century this type of instrument was used in many geomagnetic observatories, above all to determine the vertical Z component of the Earth’s magnetic field.
The instrument and method of measurement were devised by the Irish physicist Humphrey Lloyd, around 1842. The magnetometer was mounted on a horizontal slab, rectified with the aid of a level. The 30.5 cm long steel magnetic bar rested on agate bearings by means of a triangular knife. To protect it from air flow and to ensure thermal insulation, the bar was closed in a box, in which a thermometer was inserted.
In his publications Secchi highlighted the stability and quality of the response of the instrument and noted that the major drawbacks were due to insects that, not caring for scientific research, often crept into the scales and prevented the correct operation.

Aldo Altamore - Università degli Studi “Roma Tre”
Marco Faccini - INAF-Osservatorio Astronomico di Roma

Bibliography
A. Altamore & N. Ptitsyna, "il primo osservatorio geomagnetico d'Italia" in A. Altamore e S. Maffeo, Angelo Secchi. L'avventura del Scientifica del Collegio Romano, edizioni Quader, Foligno, 2012.