A Comparison of the Records from British Magnetic Stations Underground and Surface

During nearly six years a weekly statement of 2-hourly declination values was issued from Kew Observatory for the benefit of mining engineers. This helped to bring to the front the question of how far data from an observatory in the S. E. of England apply to the British coalfields. So far as we know, the only previous investigation in which continuous records were obtained from neighbouring underground and surface magnetographs was carried out in 1906 near Dortmund, in Germany. In a short preliminary account, Prof. Ad. Scbmidt, of Potsdam, stated that only trifling differences had been observed between the surface and underground stations, and that doubts existed as to whether their cause was natural or artificial. So further discussion seems to have been published. In 1920 the question of special observations in a mine was raised by Mr. T. G. Bocking, M. I. Min. E., of Birmingham, and this led eventually to the present investigation. The scheme having been approved by the Director of the Meteorological Office, Mr. Bocking secured the co-operation of Mr. H. W. Hughes, (General Manager of the Diamond Jubilee Pit at the Sandwell Park Colliery, West Bromwich (52°.5 N. lat.), and accommodation was provided for magnetographs. Two old eye-reading declinometers in stock at Kew Observatory were transformed into magnetographs by Mr. R. E. Watson, and some changes were made to a Krogness H (horizontal force) magnetograph to render it more sensitive. Messrs. Bailey, of Birmingham, a firm of mining engineers in which Mr. Bocking is a partner, kindly arranged that the immediate charge of the instruments should be undertaken by Mr. S. W. Howarth, one of their assistant surveyors, and they afforded facilities at their office for the development of the photographic traces. The instruments were set up by Mr. Watson near tbs end of March, 1923, the H magnetograph and one of the D (declination) magnetograpbs being underground, and the second D instrument at the surface. Records were taken until the middle of the following November, but operations were suspended during July and August and part of September. The underground and surface D instruments were interchanged in September, as a precaution against instrumental uncertainties.