Throughout the year the Time Service has been based upon astro­nomical observations made at Abinger, using the Bamberg Broken Transit instrument, and at Greenwich, using Small Transit B. At Abinger, 250 observations were secured on 144 nights, and at Greenwich, 187 on 134 nights, making a total of 437 observations during the twelve months covered by this report. Owing to various staff changes, some experienced observers are no longer available, and new observers are being trained to take their places. Transit C, whose over-haul, has now been completed, will be installed at Greenwich, in place of Transit B, which will be transferred to Abinger, where it will be used for additional time determinations and for training.

1951

The Report here presented refers to the period from 1950 May 1 to 1951 April 30 and exhibits the state of the Observatory on the last named day.

The positions which had been provisionally selected [at Hersmonceux] for the P.Z.T, and the Bamberg were altered, in April, to facilitate a re-location of the P.Z.T. control-room and observers' building, in conformity with the views of the Architect.

Throughout the year the Time Service has been based upon astronomical observa­tions made at Abinger, using the Bamberg Broken Transit instrument, and at Greenwich, using Small Transit B.

At Greenwich 320 observations were secured on 166 nights, and at Abinger, 249 on 123 nights, making a total of 569 observations during the twelve months covered by this report. Transit C, referred to in last year’s report, has been set up in the Small Transit Pavilion at Greenwich, and is undergoing final adjustments. It has not yet therefore been possible to release Transit B for return to Abinger, which station has been without a second instrument since January 1948. The levels used with the Bamberg and Small Transit instruments were recalibrated by an optical method in the laboratory at Abinger.

1952

The Report here presented refers to the period from 1951 May 1 to 1952 April 30 and exhibits the state of the Observatory on the last named day.

[At Herstmonceux] contracts for the building to house the Photographic Zenith Tube, the building to hold the control console for this instrument, and the pavilion for the Bamberg Broken Transit Instrument are due to be placed. The foundations and piers for the instruments and the foundations for the buildings themselves are to be constructed departmentally.

Throughout the year the Time Service has been based upon astronomical observa­tions made at Greenwich using Small Transit B and at Abinger using the Bamberg Broken Transit instrument.

At Greenwich 201 observations were secured on 160 nights and at Abinger 308 on 135 nights, making a total of 509 observations during the twelve months covered by this report. Transit C was included in the equipment sent to the Sudan for the observation of the eclipse of February 25, so that the position of one of the observing stations could be accurately determined. It was dispatched on December 4 and has not yet been received back. Routine re-calibration of the Bamberg level has been carried out twice during the year and no change in scale value has been detected.

Details of the observations made at Abinger with the Bamberg Transit Instrument were transferred to punched cards for analysis by Hollerith equipment. As the equipment at the Nautical Almanac Office was in full use and not available for this work, a member of the Observatory staff carried out the machine operations with the Hollerith equipment of the Mathematics Division of the National Physical Laboratory, through the courtesy of the Superintendent of the Division. This Hollerith analysis has been supplemented by various investigations by conventional methods undertaken at both Greenwich and Abinger and the results are now being analysed and collated.

1953

The Report here presented refers to the period from 1952 May 1 to 1953 April 30 and exhibits the state of the Observatory on the last named day.

[At Herstmonceux] contracts have been let for the manufacture and erection of the buildings to house the Cooke R.T.C., the Photographic Zenith Tube, and the Bamberg Small Transit, The foundations for each of these buildings, as well as the piers for the telescopes, will be done Departmentally. The expected completion dates for these buildings will be much delayed, but it is still hoped that the buildings will all be erected by the end of the present year.

Throughout the year the Time Service has been based upon astronomical obser­vations made at Greenwich using Small Transit B and at Abinger using the Bamberg Broken Transit instrument.

At Greenwich 188 observations were secured on 149 nights and at Abinger 232 on 131 nights, making a total of 420 observations during the twelve months covered by this report. At Greenwich, the adjustable bubble, which had been used on Small Transit C, was mounted on the tube of Transit B on June 19. The bubble from the old striding level has been mounted on instrument C. Parallel tests between the two instruments are being made. It is intended to withdraw Transit B and to give it a thorough reconditioning, including fitting it with precision-worked chromium-plated pivots, as soon as it can safely be spared. At Abinger, observations are being made in the early morning as well as in the evening, as a control over periodic errors in the system of right ascensions.

The time determinations made at Greenwich and Abinger are reduced to the standard Greenwich meridian by the application of the appropriate adopted longitudes. It has been found that there are significant variations between the time systems defined by the two instruments. From an examination of the residuals of observations from the finally-adopted time, “observer corrections” are derived which take into account the “personal equation” of the observer concerned as well as the mean difference between his observing station and the adopted mean of the two stations, called the “station correction”. The determined “observer corrections” are, not strictly constant; for current use the adopted values are based on an examination of a series of quarterly means.

As in previous years, the astronomical observations have been corrected for the effects of polar motion, for which the current latitude variation data, communicated regularly by the U.S. Naval Observatory, are used. These provisional estimates are subsequently amended, when the polar motion data from the International Latitude Service become available. The observations, after correction for polar variation, are referred to the mean of five or six selected quartz clocks and analysed to derive values of the seasonal fluctuation in the Earth’s rotation. The values have proved to be in substantial agreement with those obtained in 1950–51, which were smaller than those derived in earlier analyses, though a slight tendency for the amplitude to show a small and persistent increase has been noticed in the last few quarters.

1954

The Report here presented refers to the period from 1953 May 1 to 1954 April 30 and exhibits the state of the Observatory on the last named day.

[At Herstmonceux] the foundations for the Photographic Zenith-Tube Pavilion are under construction and the manufacture of the pavilion is well in hand at the works of the contractors. The plans for the pavilion to house the Bamberg Small Transit are nearing completion.

At Abinger the Bamberg broken transit instrument was in use throughout the year, 204 observations being obtained on 121 nights. At Greenwich, Transit B was withdrawn from service on September 16, on the completion of the parallel tests mentioned in the previous report. Transit C was in use in the Courtyard dome until July 18; it was then transferred to the Altazimuth dome, but was returned to the Courtyard dome on January 1. Transit B was transferred from the Altazimuth dome to the Courtyard dome on July 18. Transit B was adopted as the standard Greenwich instrument until June 30, and Transit C from July 1. The number of observations at Greenwich used for controlling the clocks was 196, obtained on 152 nights. In addition, for the parallel comparison between Transits Band C there were 69 obser­vations on 69 nights, between 1953 March 25 and September 15.

The pivots of Transit B have been chromium plated, and the instrument is being re-conditioned in the workshop at Greenwich. The figure of the pivots of the Bamberg instrument, which had been in continuous operation for some six and a half years, was examined. Wear had occurred at the parts of the pivot which are in contact with the supporting Y’s and the pads of the hanging level, but the departure from circularity nowhere exceeded 1 micron and has no significant effect on the determined time.

The application of observer corrections to the time observations was discon­tinued on July 1, with the exception of a significant personal correction retained for one observer (AC). It was found that the personal equations of the observers, with this one exception, are much smaller than the fluctuating difference between the two stations, Abinger and Greenwich.

The series of morning observations undertaken at Abinger was discontinued on May 1; no significant differences of a systematic nature were detected between the morning and evening observations. A similar series was commenced at Greenwich on January 31, after Transit C had been finally mounted in the Courtyard dome.

The determinations of time have been corrected for the effects of polar motion, based on current latitude observations communicated regularly by the D.S. Naval Observatory. After this correction, they have been compared with several selected quartz clocks and analysed to derive the apparent annual fluctuation in the rotation of the Earth. The fluctuation is in close agreement with those observed in the past two or three years.

During the summer of 1953, the time determinations indicated an increasing systematic departure of the standard clocks from the performance predicted on the basis of the observations of the previous 6 to 12 months. Clock inter-comparisons gave no reason to suspect that the clocks had suffered any change, and the divergence was attributed to a change in the rate of rotation of the Earth. The magnitude and form of the change could not be precisely evaluated because of the considerable scatter in the time determinations and because of some uncertainty about the rate of frequency drift of some of the clocks. The change was represented at first as a simple decrease of 1.3 milliseconds in the length of the day, occurring in 1953 March, but subsequent evidence suggests that it was more complex, and may have occurred as early as 1952 December.

1955

The Report here presented refers to the period from 1954 May 1 to 1955 March 31 and exhibits the state of the Observatory on the last named day.

[At Herstmonceux] the small pavilion to house the Bamberg Small Transit and the pavilion for the Photographic Zenith Tube have been erected.

At Abinger the Bamberg broken transit instrument was in use for the whole of the eleven-month period covered by this Report, 180 observations being obtained on 103 nights. The contact length and the level scale value received the usual routine check in October, and the values adopted were confirmed. At Greenwich during the same period Transit C was employed in the Courtyard Dome. Altogether, 234 observations were obtained: 103 of these were made on 79 mornings, and 131 on 127 evenings. The observations at Abinger and Greenwich, totalling 414, were combined for the purposes of time determination.

It was noticed in May that the effective length of the micrometer contact of Transit C differed from the value adopted from previous measurements. There was no independent evidence to indicate precisely when the change had occurred. As the instrument had been in operational service for less than a year, it was decided to recompute the observations on the assumption that the new value of the contact length had been applicable throughout. This micrometer was replaced on June 11 by the Cooke micrometer, which had previously been used on Transit B and which had been reconditioned and the drive altered so as to double the speed of manual turning. The contact length was redetermined in June and November and was found to have the same value as used throughout its 25 years of service. Since the introduction of this micrometer the mean error of the time determinations at Greenwich has been appreciably reduced.

The determinations of time have been corrected for the effects of polar motion, based on current latitude observations communicated regularly by the U.S. Naval Observatory. Various instrumental changes have occurred, but overlapping series of observations have preserved the continuity of the polar motion adopted. After this correction, the Greenwich and Abinger time observations have been compared with several selected quartz clocks and analysed to derive the apparent annual fluctuation in the rotation of the Earth. There has been no significant change in the amplitude and phase of the observed fluctuation.

The two solar-sidereal transformers, mentioned in last year’s Report, have been delivered and tested, and one is now in operation with a 20-1 frequency divider supplying 50 cycles per sidereal second to drive a synchronous clock dial in the Bamberg hut. This is an experimental installation for providing experience in the operation of the time distribution system that is being planned for Herstmonceux.

1956

The Report here presented refers to the period from 1955 April 1 to 1956 March 31 and exhibits the state of the Observatory on the last named day.

At Greenwich, astronomical time determinations were made throughout the year with Transit C in the Courtyard Dome, 99 observations being obtained on 96 mornings and 160 on 157 evenings. The reduction in the mean error of the observations, referred to in last year's report, has been maintained. At Abinger, the Bamberg broken transit instrument was removed from service on 4 November for replacement of the wiring which had become faulty on account of condensation. The opportunity was taken to give the instrument a mechanical overhaul. When observations were resumed, there appeared to be a discrepancy of some 100 milliseconds. In spite of various efforts to locate the cause, it was not until 17 February that backlash between the lead-screw and the wire carriage was detected by means of a displacement indicator gauge. On further dismantling the micrometer it was found that the return spring was oversize for its housing. A new spring was made and inserted, but was apparently of insufficient strength. A third spring was made and inserted on 23 March. Subsequent observations indicate that the discrepancy persists, and the investigation continues. In all, 232 observations were taken on 138 nights, of which only 146 on 89 nights were used for time determination. The combined total for the two stations of observations used for time determination was thus 405.

No further references to the Bamberg Instrument were made in the later Reports. Although as late as 1955, there were still plans to install the Bamberg Instrument at Herstmonceux this doesn't appear to have happened, Small Transit Instrument C having been placed in the pavilion instead. Details of this were given in the Report for 1958 which covered the period 1 April 1957 to 31 March 1958:

Observations made with the Small Reversible Transit C were used until October 16 [1957] in the establishment of the provisional time system employed for the adjustment of the clocks controlling the radio time signal transmissions. It was moved from the Courtyard Dome at Greenwich following an observation on April 23 [1957] at 03.9 U.T. and transferred to Herstmonceux, where the first observation was obtained on April 23 at 20.0 U.T.

From October 16 [1957] the P.Z.T. observations were used exclusively in current work, and retrospectively from July for the establishment of the definitive time system given in the Time Service Bulletin.