Reference numberMS/119/2/103
TitleLetter from Joseph Henry Kay, Magnetic Observatory Rossbank to Humphrey Lloyd, Trinity College, Dublin
Date16 January 1842
Description[This letter is in two parts.]

Kay replies to Lloyd's letter from 26th August, Falmouth and assures Lloyd that the suggested alterations will be made. Kay discusses the set up at the Rossbank observatory at present. Kay describes the positions of the three pillars supporting the instruments and includes a small diagram showing the declination vertical force and horizontal force instruments in relation to the magnetometer. When the instruments were first adjusted by Captain James Clark Ross in the current position, Ross conducted experiments to ascertain whether the instruments influenced one another, Kay discusses Ross's conclusions. Kay notes on their arrival to Van Diemen's Land [Tasmania; Lutruwita or Truwana], Ross lengthened the building by six feet , he placed the vertical force magnetometer in the plane of the magnetic meridian, as well making adjustments to the horizontal force magnet with Captain [Francis] Crozier and Kay.

Discussion on how the horizontal force magnet is effected by the practical adjustments. Kay describes the method Captain Ross employed to find the exact position of the torsion circle in which two readings of the scale agreed. The torsion circle was then turned 90 degrees, the collimator was turned back until the scale coincided with the vertical wire of the fixed telescope.

Captain Ross also adjusted the declination magnet, and the ony alteration Kay intends to make is to find the magnetic axis of the bar by alternate readings in the direct and reversed positions.

Kay informs Lloyd that he will make the necessary readjustments according to Lloyd's instructions including a diagram showing the arrangements of the instruments Kay intends to make. Description of the changes to the vertical force magnets position.

Discussion on the effects of the suns rays on the instruments, and the variation of the internal temperature. Kay describes the measures that have been taken to protect the instruments from the suns rays, light and currents of air, and assures Lloyd that every effort is being made in this regard. Kay intends to consult with Sir John Franklin and the Commanding Royal Engineer to discuss whether a more equable temperature may be preserved.

Discussion regarding the barometer and how readings are taken.

Kay describes his intentions to constantly repeat experiments for determining the coefficient of torsion, and the amount of torsion remaining in the suspension thread.

Discussion on the observations and deflection distance.

Kay describes their method of recording observations with the vertical force instrument.

Kay informs Lloyd he received letters from Captain Ross and Crozier dated 22nd November from the Bay of Islands, New Zealand, sailing south the next day, and they seemed in high spirits
Physical descriptionInk on paper

The letter has a hole where the wax seal has been broken.
NotesLetter MS/119/2/104 has been bound between letter MS/119/2/103
Access statusOpen
Fellows associated with this archive
NA4898Kay; Joseph Henry (1814 - 1875)1814 - 1875
NA8252Lloyd; Humphrey (1800 - 1881)1800 - 1881
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