| RefNo | MS/119/2/92 |
| Level | Item |
| Title | Letter from John Henry Lefroy, Longwood, St Helena to Humphrey Lloyd, Trinity College, Dublin |
| Date | 18 July 1840 |
| Description | Lefroy send observations and issues arising at the Longwood, St Helena observatory. Lefroy acknowledges receiving new copper rings and scales sent by Lloyd. Records the times of vibrations of the magnets at their observations. Does not know if they have lost magnetism. The relative force is in the same order as March when first compared. Lefroy apologises for keeping the magnets with the poles the wrong way the first four or five days, he notes magnet number two was covered in arsenical soap to prevent rust that he misread the letters. Asks Lloyd to provide 'the principle of the actions of the copper rings'. Discussion on the ratio of the horizontal needle to the total force, and how the vertical needle looses magnetism. Notes one of the micrometer springs is out of order which provides different readings, and suggests if someone could fix this. Lefroy notes the dipping needles are 'indifferent', and was not able to find a needle mentioned in the survey of Great Britain, whose errors can be compared with those recorded. Notes they reduced the difference in reversing the poles. Discussion on adjusting the magnet to move the telescope in order to get it into the meridian. Asks Lloyd to thank Mr [Thomas] Grubb on his behalf for the scales he presented to the [St Helena] observatory. |
| Extent | 4p |
| Format | Manuscript |
| PhysicalDescription | Ink on paper |
| AccessStatus | Open |
Fellows associated with this archive
| Code | PersonName | Dates |
| NA7669 | Lefroy; Sir; John Henry (1817 - 1890) | 1817 - 1890 |
| NA8252 | Lloyd; Humphrey (1800 - 1881) | 1800 - 1881 |