Reference numberMS/119/2/106
TitleCopy of a letter from Humphrey Lloyd, Falmouth to Joseph Henry Kay, with Kay's reply to Lloyd forwarded to James Clark Ross, 'HMS Erebus'
DescriptionIncludes a verbatum copy from Lloyd to Kay, written by Kay on the left side of the page, dated 26 August 1841. A correct copy of Kay's reply to Lloyd, with some abridged parts, not essential to the important topics is written on the right side of the page, dated 16 January 1842.

Discussion on the Rossbank observatory [located in Tasmania, then colonial Van Diemen's Land]. Lloyd enquires on what grounds Kay had disposed the three instruments, arguing that the disposition will not correct the mutual action of the magnets. Lloyd agrees with Kay that the building is not adaptable to the arrangements previously described by Lloyd in his paper. Lloyd recommends a useful disposition of the instruments to Kay, including a small diagram representing the planes of declination, vertical force and horizontal force magnets and their position, and explains its advantages. Lloyd discusses how to obtain the ratio of the strengths V divided by H, and recommends not to move the pillar, but the direction of the magnet is easily altered.

Kay discusses the position of the plane of declination, vertical and horizontal force magnets. Kay includes a small diagram showing the declination and vertical force magnets in the magnetic meridian, and the horizontal force magnet at right angles to it with the north pole to the west. Kay discusses Captain [James Clark] Ross’s adjustments to the instruments when they were first installed, and Ross’s experiments to ascertain whether the instruments exerted any influence on each other. The vertical force magnetometer was placed by Captain Ross in the plane of the magnetic meridian.

Discussion on the adjustment of the vertical force magnet made by Captain Ross. Kay notes that he was instructed not to change the adjustment of any of the instruments unless accidental circumstances permitted it.

Lloyd discusses a defect in Kay’s observation on the great variation of the internal temperature.

Kay considers Lloyd’s question regarding whether the sun play upon the instrument. Kay notes that every precaution has been made to protect the declination, horizontal force and vertical force instruments form the sun’s rays, light, and currents of air by canvas screens stretched across the building. Discussion on the various ways the vertical force instrument is protected. Kay informs Lloyd that he will contact the Royal Engineer to enquire if it is possible to preserve a more equable temperature. Kay suggests that the building itself and the external temperatures may be the cause of this variation, however he will make every effort to remedy this if possible.

Lloyd asks Kay if it is inconvenient to place the barometer at such a distance from the other instruments. Kay discusses the position of the barometer.

Discussion on the adjustments of the declination magnetometer. Lloyd informs Kay that he will need to use the long scale with 500 divisions in experiments of absolute intensity, and all deflection experiments, rather than the short scale Kay is currently using. Kay replies that he does possess the scale with long dimensions. Kay will conduct experiments to determine the coefficient of torsion repeatedly. The horizontal force magnetometer will be readjusted.

Lloyd informs Kay to use the brass bars to determine the amount of torsion remaining, as currently Kay’s observation determines the coefficient.

Discussion on the horizontal force magnetometer. Lloyd points out errors made by Kay in the observations.

Discussion on the observations of absolute intensity. Lloyd notes that Kay’s deflection distances are too great, and deflections too small. Lloyd advises on a suitable distance, and when observations need to be made for horizontal force instrument.

Lloyd expresses his confusion regarding Kay’s mode of recording he readings of the vertical force instrument and provides suggestions to correct this.

Kay mentions in his report the even hours of Göttingen mean time correspond to ten minutes after the even hours of mean time at the observatory. Lloyd notes this should not be the case. Kay replies about the mistakes he found with the Göttingen mean time.
Physical descriptionInk on paper
Access statusOpen
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