Minor oscillations of Magnetographs

Abstract

At the Alibag Magnetic Observatory, two sets of photographic magnetographs have been in use for several years past. The magnetograph room is an insulated cubicle with double walls, double roof and double basement. A working floor or basement of flagstones is supported by trusses several feet above the ground. Isolated pillars with circular guard air-spaces come up through the insulating layers and the working floor of flagstones right from the ground. The Watson magnetographs (horizontal force, H; declination, D; and vertical force, V) and their recorders have rested on these isolated pillars since 1903-4. The La Cour magnetographs and their recorders are on pillars erected only above the working floor, with no rigid connexion to the ground below. The D instrument has been in use since 1936 and the H and V instruments have been in use since 1946.