Each observatory is supplied with three magnetometers, or bars of magnetized steel, delicately suspended by threads of raw silk, which measure the magnetical declination, horizontal intensity, and vertical force—and such astronomical apparatus as is required for ascertaining the time and the true meridian. To these have also been added in each case a most complete and perfect set of meteorological instruments, carefully compared with the standards in possession of the Royal Society, not only for the purpose of affording the necessary corrections of the magnetic observations, but also with a view to obtaining at each station, at very little additional cost and trouble, a complete series of meteorological observations. In order that the observations may be made at the same periods of time, it was resolved that the mean time at Göttingen should be employed at all the stations, without any regard to the apparent times of day at the stations themselves. Each day is supposed to be divided into twelve equal portions of two hours each, commencing at all the stations at the same instants of absolute time, which are called the magnetic hours. At the commencement of each period of two hours throughout the day and night, with the exception of Sundays, the magnetometers are observed, and the meteorological instruments read off. Independently of these observations, others are made at stated periodical intervals every two minutes and a half during twenty-four hours. These are known by the name of “turn-day observations.” Printed forms for registering the observations have been prepared with great care, in order that a complete form of registry may be preserved—a point of great importance, when it is remembered that all the observations made at the different stations must eventually be reduced and analyzed. A singularly felicitous adaptation of photography has been carried into effect with the magnetometers. By means of mirrors attached to their arms, reflected light is cast on highly-sensitive photographic paper wound round a cylinder moved by clockwork, and the slightest variation of the magnets is registered with the greatest accuracy.