Reference numberMS/119/2/82
TitleLetter from Frederick Marow Eardley-Wilmot, Cape of Good Hope Observatory to Humphrey Lloyd, Trinity College, Dublin
Date10 July 1841
DescriptionEardley-Wilmot sends Lloyd the returns for June [not enclosed]. Discussion regarding temperature experiments, and correction for temperature derived from deflection. For repeating these experiments of vibrations at dipping temperature, Eardley-Wilmot made a large water cask into an underground room.

Eardley-Wilmot informs Lloyd that Lefroy has just forwarded him Lloyd’s various letters. From them Eardley-Wilmot was able to fix the vertical force to the magnetic meridian and increase its sensibility. However, he is unable to get a value for finding the deviation of the magnetic axis from the line joining the crosses. Eardley-Wilmot has obtained the dip in the magnetic meridian several times. Discussion on the effect of the temperature.

The dip will be taken Tuesdays and Fridays, and as specified by [Edward] Sabine it is to be taken in all the different azimuths at each set.

The horizontal force is showing signs of decreasing the torsion force. Eardley-Wilmot removed the magnet and turned the torsion circle into the position of the magnetic meridian, it did not come back to the same reading it had before by eight or nine divisions. Eardley-Wilmot discusses that this should not be the case.

Discussion on the removal of the declination bar, ascertaining its magnetic axis, and experiments for vibrations will carry on Eardley-Wilmot’s subterranean room.

Discussion on the absolute declination and difficulties in obtaining the true azimuth of the portable transit.

Eardley-Wilmot discusses vibrations and adjustments to his chronometer.

Details on Eardley-Wilmot’s system of monthly measurements, as well as method of obtaining vibration and results, and sets of vibrations differing from one another in certain experiments.

Eardley-Wilmot notes the magnets this month have been steady, the vibrations have been small, but the deflection more than usual. The impact of the weather on the magnets. There is some connection between the atmospheric changes and those of magnetic intensity.

Eardley-Wilmot asks details about his plans for term days.
Physical descriptionInk on paper
Access statusOpen
Fellows associated with this archive
NA6061Eardley-Wilmot; Frederick Marow (1812 - 1877)1812 - 1877
NA8252Lloyd; Humphrey (1800 - 1881)1800 - 1881
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