John McFarland

Armagh Observatory, College Hill, Armagh, Northern Ireland, United Kingdom, BT61 9DG.

ABSTRACT. The need for registering and detailing all information relative to the history of astronomical instruments and any alterations to, or restoration of, them is stressed. This article describes the conditions under which both the historical scientific instruments and their related documentation, where now available, are catalogued and preserved at Armagh Observatory. As illustrative examples, we have selected two items of equipment which were acquired at the time of the foundation of the observatory in 1789.


The historical astronomical and other scientific instruments and equipment acquired by the Armagh Observatory during its two hundred years of existence have been catalogued in an earlier volume of this journal (McFarland 1990). Each instrument was given an identification number and photographed. All documentation relevant to the instruments which could be located either in the observatory collection of manuscripts, or in published papers were analysed and placed in chronological order, as far as could be ascertained. Inventories were produced from time to time in the course of the observatory's history and these proved most useful. One of the instruments, the Troughton equatorial telescope, is maintained at constant temperature and relative humidity, to reduce the rate of deterioration. The temperature is kept at 17C, and the relative humidity between 50 - 60%. In particular, any papers relating to the disposal, loss or modification of the equipment were documented. A loans and repairs logbook is maintained which indicates the movement of the instruments, either for repairs or exhibition purposes.


Butler & Hoskin (1987) produced a listing of all the manuscripts in the observatory archives covering the period from the 1780s until the year 1916, the year in which Dr J L E Dreyer resigned the Directorship. Many of the MSS contain references to the instruments, including drawings, and alterations to the equipment. The MSS were catalogued under topics such as observatory government, finances, administration and observations. It is most important that material of this nature, hand-written notebooks, observation record books, reduction books and so on, are copied. A major task undertaken was the microfilming of some of this material; unfortunately the project was never completed. Again, where possible, such material should be maintained at constant temperature and humidity (T=16C and RH=55%) and stored in acid-free envelopes. It is notoriously difficult to ensure that air-conditioning units are operating correctly, so constant monitoring of their performance is essential. The units must be calibrated periodically.


3.1 Troughton Equatorial Telescope

Figure 1 shows the equatorial telescope constructed by J & E Troughton of London and which was erected in the west dome of Armagh Observatory in 1795. The telescope dimensions are 2-1/2 inch aperture objective, 3-feet focal length. Figure 1(a) shows the manufacturer's drawing of the telescope, mounting and piers (Maskelyne 1789, Troughton 1792). Figure 1(b) is a photograph of the telescope in its present condition. It is recorded in the Astronomer's Annual Report for 1844, appended to the Observatory Minute Book, 1820-1958, p.38 that: "The west Equatorial while in the hands of Mr Troughton was injured by a frost which condensed on it moisture charged with the Sulphurous vapours of the London smoke, and spotted it all over" --- signed T R Robinson. Consequently, in the middle of the nineteenth century, Robinson had the instrument painted to prevent further deterioration. This paint was recently removed and the instrument cleaned and laquered. Looking at this newly revealed brass work, and seeing its fragile nature, Robinson's action in all probability saved this fine specimen of eighteenth century craftsmanship. Figure 2 is the first page of Troughton's instructions for the adjustment of the telescope (Troughton c.1790).

3.2 Earnshaw Regulator

The Astronomer Royal for England of the day, Revd. Nevil Maskelyne, requested Thomas Earnshaw to construct a regulator for Armagh Observatory and to make it as air-tight as possible. After some reluctance, Earnshaw eventually agreed and Figure 3 shows the result -- Earnshaw's first long- case clock. Some years later, Earnshaw wrote to the Astronomer at Armagh, Revd. J A Hamilton, asking him to provide testimonials for the two regulators he ultimately provided for Armagh for publication in his famous "Appeal to the Public" claiming originality in the design of his time pieces. Figure 4 is a reproduction of Earnshaw's letter to Hamilton (Earnshaw 1807).


In summary, it is vital to catalogue an observatory's scientific instruments and their associated documentation for ease of retrieval for the use of science historians. Master copies of manuscript holdings should be made and any further copies required should be made from these masters. The MSS should be stored at appropriate constant temperature and humidity in acid-free envelopes. All movements of instruments and MSS should be recorded in a logbook. Alterations and repairs to equipment should be detailed as fully as possible. The instruments should be photographed and an inventory formed. It is recommended that instruments should be treated with extreme care.


Dr C J Butler was responsible in large measure for initiating this programme of restoration and conservation work at Armagh Observatory. Mr M Murphy, the Starlink Manager at Armagh Observatory, has kindly provided considerable help in coverting this document into a suitable form for the World Wide Web. Armagh Observatory is granted-aided by the Department of Education for Northern Ireland. It is a pleasure to acknowledge the financial assistance received from the Friends of LISA II which enabled the author to attend this IAU Technical Workshop.


Butler, J. and Hoskin, M.: 1987, The Archives of Armagh Observatory, Journal for the History of Astronomy, Vol.18, p.285.

Earnshaw, T.: 1807, Letter from T Earnshaw, 22 December 1807, Armagh Observatory Archives, M51.9, 3pp.

Maskelyne, N.:1789, Letter from Maskelyne to J A Hamilton, 22 April 1789, Armagh Observatory Archives, M51.3, 3pp.

McFarland, J.: 1990, The Historical Instruments of Armagh Observatory, "Vistas in Astronomy", Vol.33, p.149.

Troughton, J. & E.: c.1790, Instructions for Adjusting the Troughton Equatorial Telescope, Armagh Observatory Archives, M17.2, 3pp.

Troughton, J. & E.: 1792, Letter from J & E Troughton, 7 July 1792, Armagh Observatory Archives, M51.7, 3pp.

Last Revised: 2011 June 27th