Reference numberMS/119/2/13
TitleLetter from Humphrey Lloyd, Dublin to Charles James Buchanan Riddell, Magnetical Observatory, Toronto, Canada
Date24 July 1840
DescriptionLloyd answers Riddell’s questions regarding the work at the Toronto observatory. Lloyd informs Riddell of his recent marriage. Lloyd will be travelling with his new wife to the 'continent' in a few days and hope to meet the Sabine’s in Switzerland.

Lloyd, [Edward] Sabine and [Thomas Romney] Robinson agreed that a new vertical force magnetometer should be sent to Riddell, and to understand the instructions. Lloyd advises not to move the axle, and that it is unnecessary that the centre of gravity should coincide with the magnetic axis. The only areas of concern are underneath the magnetic horizontal axis and they make the entire instrument as sensible as possible which is affected by the vertical screw.

Lloyd discusses the coefficient and informs Riddell it depends on the ratio of the times of vibration in the vertical and horizontal planes, and how the two differ. Lloyd suggests the observation of the time of vibration should be repeated once a week in this season. Lloyd's own vertical force magnetometer took a new position when it was removed from the agate planes. Discussion on how Robinson has overcome this difficulty.

Discussion regarding replacing the horizontal force magnetometer form its stirrup causing a small change in the reading. Riddell mentioned that some of his bars are weak, and Lloyd notes this makes matters a little more complicated.

Discussion on the arrangement of the magnets in the observatory. Lloyd discusses the correspondence in the movement of the magnet at Toronto, Brussels, Dublin and Prague, movements of declination at Philadelphia and Dublin.
Physical descriptionInk on paper
Access statusOpen
Fellows associated with this archive
NA8252Lloyd; Humphrey (1800 - 1881)1800 - 1881
NA7327Riddell; Charles James Buchanan (1817 - 1903)1817 - 1903
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