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Abstract
British physicist, Louis Essen (1908–1997), is remembered for his achievements in the field of precision timekeeping. This paper focuses on his work on time signals and standard frequency transmissions. The unit of time is one of the most basic measurements in science and Essen was responsible for its transformation from the solar system and astronomy to the atom and physics. This paper examines his role in the adoption of Coordinated Universal Time and the birth of atomic timekeeping. Essen also compared the performance of clocks on either side of the Atlantic using radio waves as well as microwaves. He also synchronised his atomic clocks with similar American clocks in side-by-side comparisons of their accuracy and stability. In the 1950s, Essen participated in a series of US-UK experiments which led to the development of the first global all-weather radio-navigation system for both military and civilian use.
Acknowledgements
My grateful thanks to the National Physical Laboratory and to Denis Sutcliffe for his help over many years. Denis joined NPL in 1949 and worked with Louis Essen on atomic clocks and time synchronisation between 1955 and 1972. He retired from NPL in 1988.
Notes
1 J. Jespersen and J. Fitz-Randolph, From Sundials to Atomic Clocks (New York: Dover Pubs., 1999), p. 4.
2 L. Essen, The Memoirs of Louis Essen, Father of Atomic Time (Teddington: National Physical Laboratory, 2015), pp. 98–9.
3 BIPM, 13th General Conference on Weights and Measures (CGPM), Paris. Meeting Report 1967–1968, p. 23. Defines the second in terms of a property of the caesium atom.
4 For the atomic redefinition of the second, see also: M. A. Lombardi, ‘A Historical Review of US Contributions to the Atomic Redefinition of the SI Second in 1967’, Journal of Research of the National Institute of Standards and Technology, 122, 29 (2017), 1–17.
5 Jespersen, p. 7.
6 P. Whibberley, ‘NPL Contribution to the Introduction of the Caesium Second’, PTB-Mitteilungen, Heft 3, 127 (2017), 33–9.
7 S. Leschiutta, ‘The Definition of the Atomic Second’, Metrologia, 42, 3 (Jun. 2005), S10–S19.
8 Conclusions of ‘Report of the committee to consider the desirability of establishing a National Physical Laboratory’ (London: HMSO, 6 July 1898) 1376, p. 8.
9 Essen, Memoirs, p. 19.
10 Quantum metrology is the precise measurement of physical parameters using quantum theory.
11 L. Essen, ‘The Caesium Frequency Standard’, NPL News, No. 65 (15 Sep. 1955).
12 E. Pyatt, The National Physical Laboratory (Bristol: Adam Hilger, 1983), pp. 141–9.
13 D. Sutcliffe, ‘An Extract of Atomic Clock References from NPL Executive Committee Minutes, 1948–1958’.
14 For a more extensive bibliography about Louis Essen’s work, see: R. Essen, Revolutions in Time: The World of Louis Essen, Clockmaker and Father of Atomic Time (Amazon: independent publisher), pp. 421–42.
15 P. Forman, ‘Atomichron: The Atomic Clock from Concept to Commercial Product’, Institute of Electrical & Electronic Engineers, 73 (1998), 1181–204.
16 Essen, Memoirs, p. 92.
17 Royal Greenwich Observatory Archives (Cambridge Digital Library).
18 D. Howse, Greenwich Time and the Longitude (London: Philip Wilson, 1997), pp. 88–9.
19 Howse, p. 84.
20 In the case of Ireland, time was held to be ‘Dublin mean time’ in the Act of Parliament (1880).
21 Howse, p. 136.
22 B. Guinot, ‘History of the Bureau International de l’Heure’, Polar Motion: Historical and Scientific Problems, ASP Conference Series, Vol. 208 (2000).
23 The International Astronomical Union (IAU) is a non-governmental organisation founded in 1919. Its mission is to promote and safeguard the science of astronomy in all its aspects through international cooperation.
24 S. Dick, Sky and Ocean Joined: The US Naval Observatory 1830–2000 (Cambridge: University Press, 2007), pp. 451–78.
25 Howse, p. 158.
26 M. Hancock, The History of Rugby Radio Station (London: Urban & Civic, 2017), p. 32.
27 L. Essen, The Measurement of Frequency and Time Interval (London: HMSO, 1973), p. 23.
28 L. Essen, ‘Standard Frequency Transmissions in the UK’ Journal of the Institution of Telecommunication Engineers, 12.4 (1966), 257.
29 L. Essen, ‘International frequency comparisons by means of modulation emissions’ Journal of the Institution of Electrical Engineers, 75.452 (1934), 289–92.
30 L. Essen, ‘Standard Frequency Transmissions’, p. 250.
31 The name ‘Royal Greenwich Observatory’ dates from 1948 at the start of the move from Greenwich to Herstmonceux Castle in East Sussex. Before then, it was known as the Royal Observatory at Greenwich. G. Wilkins, ‘A Personal History of the Royal Greenwich Observatory’, Vol. 2 (2009), Cambridge University Library.
32 H. Spencer Jones, Letters from the Astronomer Royal to Sir Edward Appleton, Cambridge University Library, Manuscripts Dept., Ref. RGO-9-630 (1948–1950).
33 Hancock, p. 222.
34 Essen, Memoirs, p. 36.
35 J. A. Pierce, ‘Presentation of the Elmer A. Sperry Award for Advancing the Art of Transportation’, IEEE GLOBECOM ’88 Conference (30 Nov. 1988), biography of awardee.
36 Internatl. Omega Assocn. Newsletter, Part III (1988), p. 1.
37 Pierce, Presentation, p. 2.
38 Hancock, p. VII.
39 J. Pierce ‘Memoirs of J. A. Pierce’, unpublished (4 Feb. 1989).
40 L. Essen, H. T. Mitchell, and J. A. Pierce, ‘Worldwide Frequency and Time Comparisons by Means of Radio Transmission’, Nature, 173 (1954), 192.
41 J. Pierce, ‘The Diurnal Carrier-Phase Variation of a 16-Kilocycle Transatlantic Signal’, Cruft Lab. Harvard, Tech. Rep. 209 (10 Oct. 1954).
42 Essen, Memoirs, p. 72.
43 J. Pierce, Letter to L. Essen (30 Nov. 1956).
44 W. Markowitz, ‘Reminiscences of the US Naval Observatory’, unpublished oral history interview on deposit in USNO library (21 Oct. 1986).
45 The ninth General Assembly of the International Astronomical Union (29 Aug. – 5 Sep. 1955). Approximately 600 astronomers attended from 41 countries.
46 M. Thomson, ‘Canadian Scientists Report XI – The Dual-Rate Moon-Position Camera’ Journal of Royal Astronomical Society of Canada, 52 (1958), 112.
47 W. Markowitz, R. Hall, L. Essen and J. Parry, ‘Frequency of Caesium in Terms of Ephemeris Time’, Physical Review Letters 1 (1958), 105–7.
48 L. Essen and J. McA. Steele, ‘The International Comparison of Atomic Standards of Time and Frequency’, Proc. IEE, 109 Part B, 43 (1962), 41–7.
49 Pierce, ‘Memoirs’.
50 L. Essen and J. McA. Steele, p. 41. The numbering of Atomichrons started at 100 which meant that some of the earliest US atomic clocks were sent to NPL.
51 F. H. Reder, ‘Minutes of Coordination Conference on Comparison of US and UK Caesium Beam Standards’, US Army Signal Engineering Labs., Fort Monmouth, New Jersey (24 Feb. 1958), Appendix 1.
52 URSI (International Union of Radio Science), Golden Jubilee Memorial (Brussels, 1963) p. 25.
53 J. Holloway, L. Essen et. al., ‘Comparison and Evaluation of Caesium Beam Atomic Frequency Standards’, Proceedings of the Institute of Radio Engineers, 47 (1959), 1730.
54 National Company sales brochure, ‘The National Atomichron: Tuned to Tomorrow’, p. 6 (1956).
55 Dick, p. 493. Also private communications with H. M. Smith.
56 Markowitz, Reminiscences, pp. 29–30.
57 Dick, p. 493.
58 Essen, Memoirs, p. 92.
59 A. C. Clarke, ‘Peacetime Uses for V2’, Wireless World (Feb. 1945), p. 58.
60 W. C. Jakes, ‘Participation of Bell Telephone Laboratories in Project Echo and experimental results’. NASA tech. note D-1127 (Dec. 1961).
61 D. Sutcliffe, unpublished memoirs and private communications with author (2010–2020).
62 Sutcliffe, Memoirs.
63 W. Markowitz, private letter to D. Sutcliffe (5 Jan. 1979). The General Post Office (the UK telecommunications carrier prior to 1969) operated the UK earth station used for communicating with Telstar.
64 L. Essen, ‘Standard Frequency Transmissions’, p. 265. Also J. McA. Steele et al., ‘Telstar Time Synchronisation’, IEEE Transactions on Instrumentation and Measurement, IM-13, 4 (1964), 164–70.
65 Sutcliffe, Memoirs.
66 Essen, Memoirs, p. 92.
67 Jespersen, p. 118.
68 J. Bonanomi, former director of Neuchatel Observatory, Switzerland. Communications with author (1999–2005).
69 A. S. Bagley and L. S. Cutler, ‘A New Performance of the Flying Clock Experiment’, Hewlett-Packard Journal, 15.11 (Jul. 1964). See also Hewlett-Packard Journal 1965, 1966 and 1967.
70 Sutcliffe, Memoirs.
71 L. Essen, ‘Atomic Time and the Definition of the Second’, Nature, 178 (7 Jul. 1956), 34–5.
72 Essen, Memoirs, p. 72.
73 Ibid, p. 72.
74 Ibid, p. 72.
75 Atomic time is now kept within 0.9 seconds of astronomical time. The future of the leap second is being discussed by a number of organisations including the International Bureau of Weights and Measures, Paris.
76 A. Cook, ‘Louis Essen O.B.E.’, Royal Society Biographical Memoirs (1998), 143–58.
77 Dick, p. 494.
78 M. du Sautoy, Mathematician & Science Communicator, Precision: the measure of all things, time & distance (BBC Four, 2013).
Additional information
Notes on contributors
Ray Essen
Ray Essen has written extensively about horology and the work of his late father-in-law, Louis Essen. His latest book, Revolutions in Time, tells the story of the birth of atomic timekeeping and the impact it had on the development of broadcast radio, radar, navigation and radio astronomy. He has a degree in physics and was a Chartered Engineer until he retired in 2009.