I. An Account of Observations made in Scotland on the Distribution of the Magnetic Intensity

Abstract

Makerstoun, Kelso, 15th March 1830.My Dear Sir,Accompanying I beg leave to transmit you Mr Dunlop's paper on the distribution of the magnetic intensity over this country, which I formerly mentioned when I had the pleasure of seeing you, and which I request you will lay before the Royal Society.Mr Dunlop has so fully and clearly detailed his mode of proceeding with these observations, that it would be unnecessary for me to enlarge upon them further, than to state, that, in point of number, extent of country, combined with precaution, accuracy, and consistency, I consider they are unrivalled in this or any other country.

Observations of the Earth's magnetic field made in Edinburgh from 1670 to the present day

“…The famous Danish physicist Hans Christian 0rsted made measurements of the horizontal intensity (H) in 1823 behind Coates Crescent. According to Dunlop (1830) the results were nearly the same as Dunlop's observations in 1829 at 8 St Colme Street (see below).…”

“…This was the first magnetic survey of any extensive part of the landmass of the British Isles. Dunlop (1830) measured the (relative) horizontal intensity (H) at 36 stations in Scotland and the north of England. He used an instrument belonging to the Royal Society of Edinburgh that had been provided by Professor Christopher Hansteen of Christiania (now Oslo), a pioneer in measuring the strength of the geomagnetic field.…”

“…The following morning, at Canaan Cottage, he made a further three measurements, two with the flat needle and one with the cylindrical needle. In a summary table Dunlop (1830) expresses his H values relative to a value of H= 10 at Canaan Cottage. James Forbes used the same instrument during three European journeys, on which he made many observations of H (and of the inclination /, some of which have been mentioned in Section 2).…”

“…Because of the rapid changes in the magnetisation of the fiat needle and the corresponding uncertainty in the value of K, the results obtained with it will not be considered further in this paper. Dunlop (1830) had used the same instrument, with the same needles, in 1829. If we assume that the cylindrical needle had not changed magnetically or mechanically since then, we can use the value of K just derived to convert Dunlop's periods of oscillation for this needle into values of H in nanoteslas.…”

“…The longitudes given in the earlier sources are not always with respect to Greenwich. Dunlop (1830) gives the longitudes of his stations with respect to Edinburgh; an approximate longitude of 3° 13' west of Greenwich has therefore been assigned to his Edinburgh stations in Table 5. Forbes (1837Forbes ( , 1840 and Bache (1841b) use Paris as the zero for their longitudes; they have been converted to longitudes with respect to Greenwich using 2 °20'E of Greenwich for the longitude of Paris.…”