Description of a set of magnetographs designed by W. Watson

Some time ago I designed a set of magnetographs to be used in determining the disturbances produced by an electric railway on the three magnetic elements, the experiments being made with the view to the framing of regulations for the protection of the English magnetic observatories. Since observations had to be made at a number of stations, and accommodation for the instruments was often very rough, generally stables and sheds, it was essential that the instruments should be easily and rapidly set up and adjusted, also that they should not require a darkened room. Captain Fraser, the director of the magnetic survey of India, having seen these instruments, asked me to design a set on similar lines for use at the four base stations of that survey, and although I can not claim any novelty for the arrangement as a whole, yet it has been suggested to me that a short description of the instruments might be of use to others who have to design such instruments. No attempt is to be made in the case of the Indian magnetic survey to keep a record of the changes in the vertical component, and thus in the attached photographs, which were taken from the Indian instruments, only the declination and horizontal intensity instruments are shown. Some photographs of the vertical intensity balance used in England have, however, been added.