The Bakerian Lecture: A Magnetic Survey of the British Isles for the Epoch January 1, 1886 . to make the Declination, at some point to the east of the centre, greater thanits undisturbed value at the centre, the form of the lines must approximate to thatshown in Fig. 5. The Declination will increase rapidly with the longitude, attain amaximum value, fall to its normal value at points on the magnetic meridian whichpass through the centre—on each side of which the attracting matter is supposedto be symmetrically situated—then fall to a minimum, and finally resume its normalrate of increase. If,
The Bakerian Lecture: A Magnetic Survey of the British Isles for the Epoch January 1, 1886 . to make the Declination, at some point to the east of the centre, greater thanits undisturbed value at the centre, the form of the lines must approximate to thatshown in Fig. 5. The Declination will increase rapidly with the longitude, attain amaximum value, fall to its normal value at points on the magnetic meridian whichpass through the centre—on each side of which the attracting matter is supposedto be symmetrically situated—then fall to a minimum, and finally resume its normalrate of increase. If, retaining all the other assumptions, we suppose that the isogonals and meridiansare inclined at an angle of less than 90°, the distorted curves will assume formsoimilar to those in Fig. 6. It will be noticed that if the undisturbed isogonals be 262 MR. A. W. R1JCKER AND DR. T. E. THORPE ON A MAGNETIC rotated about A in the limiting cases when they coincide with AE or AN, thedistorted curves will assume the forms shown in Figures 3, and 4, or 5, Fig. 4. N w- 4 E W 1i * y N 987654321. E 9876543ZIS Terrestrial Isogonals running approximately north and south. True Isogonals produced by (Fig. 4) a weak, and (Fig. 5) a strong centre of attraction at A, Fig, 6. f
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectproceed, bookyear1890
