Unpublished paper, 'On the uneliminated instrumental error in the observations of magnetic dip' by Charles Chambers

Description

Chambers states that 'A single reading of one end of a dipping-needle placed in a dip-circle provided with microscopes for observing is liable to a variety of instrumental errors, which are eliminated by taking the mean of the sixteen readings of the two ends in the eight different positions included in a complete observation.' He finds that 'with the best modern instruments' a mean value results from these sixteen observations different for each different needle, and that the difference between the results obtained with two different needles is not the same at all times. The irregularities in the values of the dip observed at Mumbai leads Chambers to investigate the effect of a hypothetical irregularity in the shape of the axle of the needle, such that a section of the axle by a plane perpendicular to its axis would be elliptical instead of circular in form. Another source of error identified in the paper is the displacement of the centre of gravity of the needle from the centre of the axle, combined with inequality in the magnetisation of the needle when the poles are direct and reversed. Experience leads Chambers to the conclusion that the usual method of magnetisation, by a definite number of passes of the same pair of bar-magnets, communicates magnetism to the needle very unequally when the one end of the needle is made north and when the other end is made north. Chambers suggests it is advisable to investigate the effects of ellipticity of the axle and of displacement of the centre of gravity at the same time.

Note on front reads 'Adjunct to "Observations of the absolute direction and intensity of terrestial magnetism at Bombay."' (see AP/51/2).

Subject: Scientific apparatus and instruments / Meteorology / Magnetism

Received 15 April 1869. Read 13 May 1869. Communicated by the President [Edward Sabine].

Whilst the Royal Society declined to publish this paper in full, an abstract of the paper was published in volume 17 of the Proceedings of the Royal Society as 'On the uneliminated instrumental error in the observations of magnetic dip'.

Reference number

AP/51/3

Earliest possible date

1869

Physical description

Ink on paper

Page extent

17 pages

Format

Manuscript