Results of some long series magnetic observatory observations: Colaba (1846–1905), Pola (1847–1909), and Potsdam (1892–1900)

Magnetic work at Colaba was started in 1840, but it was not until 1846 that a regular system of observing was adopted. From that time to March, 1906, there is an unbroken series of observations. Photographic registration began in 1872. Prior to that time eye‐readings were taken every hour except on Sundays and holidays.