| RefNo | MS/119/2/72 |
| Level | Item |
| Title | Letter from Humphrey Lloyd, 17 Fitzwilliam Square, Dublin to Charles James Buchanan Riddell |
| Date | 28 January 1846 |
| Description | Lloyd comments on Riddell’s instructions and answers his questions as well as he can. Lloyd notes that he has been extremely busy with University [of Dublin] business, and now has a spare moment to remark on Riddell’s letter.
Lloyd discusses page three [of Riddell’s instructions], relating to the theodolite magnetometer and its incapability of the exact connection for torsion. This does not differ from any other instrument. Lloyd describes his instrument and asks Riddell to omit the note at the foot of this page.
Lloyd discusses page four, relating to the history. Lloyd notes that Mr [Karl] Kreil’s instrument was devised by [Carl Friedrich] Gauss, and Lloyd’s instrument is only a modification of Gauss’s. Lloyd discusses the modification on his instrument and informs Riddell that the disposition of the divided circles was Gauss’s idea.
Lloyd discusses page five, relating to the length of the induction bars. Lloyd discusses the results of his original experiment that showed there was not much gained from increasing it beyond 12 and 15 inches, the diameter remaining at three quarter of an inch. Discussion on the total angle of deflection, Lloyd’s original octagonal box, induced magnetism increased by [Johann von] Lamont’s dipping process, and magnetism which increases with time.
Lloyd discusses page seven, relating to the collimator magnets, and his reason for using the table top in the theodolite magnetometer, to remove the magnet from the brass work in the observation of absolute declination.
Description of Lloyd’s instrument and the object glass of the telescope.
Lloyd discusses page nine, and states that he has never used a metal ring for inertia. Lloyd informs Riddell that he has never used the small bifilar apparatus.
Lloyd advises Riddell that the statement at the top of page ten, is not clear that the original correction was Lamont’s and Lloyd provided a correction to this. Discussion on Riddell’s use of zero on this page.
Lloyd disagrees with Riddell's statement on page eleven about difference of the absolute values at fixed observatories.
Lloyd discusses the use of glass scales as presented on page thirteen.
Lloyd’s opinion on Riddell’s experiments on induced [force] in iron bars.
Lloyd is sending Riddell copies of an account of the Director of their museum (a most 'enterprising naturalist’), on the progress he has made, and would like these to be distributed to the observatory stations. |
| Extent | 8p |
| Format | Manuscript |
| PhysicalDescription | Ink on paper |
| AccessStatus | Open |
Fellows associated with this archive
| Code | PersonName | Dates |
| NA8252 | Lloyd; Humphrey (1800 - 1881) | 1800 - 1881 |
| NA7327 | Riddell; Charles James Buchanan (1817 - 1903) | 1817 - 1903 |