7 - La Cour's variometer and recording system
La Cour's magnetograph
Designed in Denmark by D. La Cour, over one hundred La Cour magnetographs were made by the Danish Meteorological Institute from 1926 onwards and were installed in French observatories in Terre Adélie and in Kerguelen in 1957 for International Geophysics Year. The La Cour variometers in Dumont d'Urville were in use until 1983.
The La Cour's magnetograph is an assemblage of fixed apparatus which detect and record variations in time of three different elements of the Earth magnetic field:
- the sensitive element of horizontal variometers (D variometer and H variometers) is constituted by a magnet with a horizontal magnetic axis suspended from a quartz thread;
- the sensitive element of vertical variometer is made of a magnet moving around a horizontal axis, this is a magnetic balance;
- the recording element of the la Cour magnetograph allows us to obtain a photograph of the variations in elements of the magnetic field. Every day the operator removes a recording sheet (a magnetogram) by which the day's magnetic activity can be visualised.
How does it work?
This set of fixed apparatus detects variations in time of three independent elements of the Earth magnetic field (H,D,Z or X,Y,Z). Each apparatus has a magnet with a flat mirror, and the mirror's rotations are proportional to the variations in the element considered. The indications given by these three apparatus can be recorded.
The variometers' sensitivity is determined using calibrating coils. Helmholtz coils are used, creating an easily calculable magnetic field during the passage of a continuous current of which the intensity is measured.
The H variometer, the Z variometer - also called the Godhavn balance - and the D variometer or "Copenhagen declinometer" were designed from 1926 onwards by D. La Cour. The Copenhagen declinometer is presented separately because it was never used in French observatories in austral and antartic regions.
Designed in Denmark by D. La Cour, over one hundred La Cour magnetographs were made by the Danish Meteorological Institute from 1926 onwards and were installed in French observatories in Terre Adélie and in Kerguelen in 1957 for International Geophysics Year. The La Cour variometers in Dumont d'Urville were in use until 1983.
