Paper, 'Note on the irregularities in magnetic inclination on the west coast of Scotland' by Thomas Edward Thorpe and Arthur William Rucker

Description

Thorpe and Rucker write: 'In the Report of the results of the Magnetic Survey of Scotland, undertaken at the request of the British Association by the late Mr. Welsh during the years 1857 and 1858, it is stated by Professor Balfour Stewart (by whom the observations were reduced and the report drawn up) that the values of all the elements as determined in and adjacent to the Island of Mull were apparently largely affected by local attraction, and from a comparison of the various observations Professor Stewart was led to place the centre of the disturbance a little to the south of the Mull stations, and at a considerable depth below the surface. The effect of this local attraction was most apparent in the determination of the dip, which at Tobermory was upwards of 57', and at Glenmorven, on the other side of the Sound, was 14' in excess of the probable normal value, that is, the value unaffected by local disturbance and dependent merely on geographical position, as deduced by combining together all the other observations for Scotland, in the manner adopted by Sir Edward Sabine in discussing the observations of the previous Survey of 1836. Dr. Stewart’s localisation of the centre of disturbance was based partly on a consideration of the abnormal values exhibited by the observations made at the two stations on the Sound of Mull, and partly on certain irregularities manifested by the determinations taken on Islay and in Skye. So far as the Mull observations themselves were concerned, the clue as to the exact locality of the area of disturbance was of the very slenderest. Mr. Welsh appears to have made only a single observation of the dip at Tobermory; and although observations were made with two needles at Glenmorven, the divergence between the resultant values happens to be greater than is exhibited by any other pair of dip observations throughout the survey. Nevertheless, as we shall show, we are able to confirm not only the general accuracy of Mr. Welsh’s observations on this particular point, but also Professor Stewart’s inference as to the probable locale of the area of disturbance.'

Annotations in ink. Includes a table of magnetic observations made at various stations on the west coast of Scotland.

Subject: Magnetism

Received 20 October 1883. Read 15 November 1883.

A version of this paper was published in volume 36 of the Proceedings of the Royal Society as 'Note on the irregularities in magnetic inclination on the West Coast of Scotland'.'

Reference number

PP/4/2

Earliest possible date

1883

Physical description

Ink on paper

Page extent

9 pages

Format

Manuscript