Abstract
AN account of a minute magnetic survey of a small district in Baden, adjacent to the Rhine, where there is considerable local magnetic disturbance, has been received from the author.1 Observations of horizontal force were made at nearly 400 stations, and observations of declination and inclination were made at about 140 of them. The object seeriis to have been to observe at a large number of stations with moderate accuracy in a short time. In fact, most of the data recorded in the tables on pp. 6-26 seem to have been obtained in the two months August and September of 1898. Horizontal force was observed only to the nearest 0′001 C.G.S., and declination and inclination usually only to the nearest 0°′1. Within the narrow region dealt with-some 150 square kilometres-declination was observed to vary between 3° 7 W. and 20° 8 W., inclination between 22°′6 and 72°, and horizontal force between 0.173 anc 0.227 C.G.S. In a district so disturbed, it would have been of doubtful advantage to have employed superior instruments, giving a higher order of accuracy than that actually aimed at. The results are embodied in four charts, which give respectively the lines of equal horizontal force, ttie isoclinals, the isogonals, and particulars of the horizontal and vertical components of the disturbing force system. The chief conclusions appear on p. 39. The most interesting of them is that the basaltic rocks-using basaltic in a general sense-which form the chief hills in the district, behave mostly like vertical magnets with their north poles uppermost. Their magnetisation is thus opposite to what it would be if induced under the action of the earth's own field. The phenomena thus differ in a remarkable way from those observed by Riicker and Thorpe in the United Kingdom. A second-somewhat interesting deduction from the observations is that there is an extension of underground basaltic masses beneath part of the level country adjacent to the Rhine near Breisach, where local disturbances would not have been anticipated from the superficial appearance of the country. The author also gives the results obtained from taking a line integral of the horizontal magnetic force round the whole district and round four subdivisions. With the exception of one of the smaller subdivisions, the departure of the line integrals from zero is very small. This may be regarded as evidence of the accuracy of the observations, if we assume that the magnetic forces are derivable from a potential, which can hardly fail to be the case so far as concerns the field answering to the local disturbances.
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C., C. Magnetic Observations in Baden . Nature 67, 187 (1902). https://doi.org/10.1038/067187a0
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DOI: https://doi.org/10.1038/067187a0