Climatological summaries of Thomas Hughes’ meteorological data, for Stroud, UK (1775-1813)

Thomas Hughes (1742–1813) kept a daily diary of weather and geoscience phenomena at Stroud in Gloucestershire, in the southern UK, between 1775 and 1813, following a short period of similar records made nearby from 1771. Data from the diary have previously been used in compiling the Central England Temperature series and to corroborate aurora sightings elsewhere in Europe. Recent historical research now confirms the suspected authorship of the diaries beyond doubt and strongly suggests that the pre-Stroud records were made in south Gloucestershire. Here, summary tables of monthly data between 1771 and 1813 are presented for thunderstorm days, snow days, rain days, rainfall, surface air pressure and auroral nights. Consistency checks, both between the different measurements contained and with other contemporary measurements, provide confidence in the reliability of the meteorological and geophysical data which spans part of the Dalton Minimum in solar activity.

summaries have not been readily available.Transcriptions of these summaries are provided here for monthly rainfall (Table 1), monthly rain days (Table 2), monthly sea level pressure (Table 3), monthly snow days (Table 4), monthly thunderstorm days (Table 5) and monthly auroral nights (Table 6).Historical thunderstorm day information is of contemporary interest (Valdivideso et al., 2019), as is meteorological data for the Dalton Minimum in solar activity, during which some of Hughes' observations were made.Thomas Hughes (1742Hughes ( -1813) ) lived in Stroud, Gloucestershire, and is buried in the churchyard of St Laurence Church, Stroud.Following his death, his medical books and papers were bequeathed in his Will (Hughes, 1813;Anon, 1813a) to the Gloucester Infirmary, for storage in the cellars of the Infirmary building.* His weather diaries were later sent to the pioneer national rainfall data collector G.J. Symons, who ultimately presented them to the Royal Meteorological Society in January 1885 (Britton, 1927).Symons (1866) does not, however, mention Hughes' data in his summary of stations measuring rainfall prior to 1800.
In their current form, the diaries exist as three bound volumes, with an adhesive cover label dated 1927 and marked 'Royal Meteorological Society'.To this, the handwritten title-'Meteorological Register kept at Stroud, Gloucestershire 1775-1813'-summarised by C E Britton in a separate file' was added (Figure 1).Charles Britton was a Met Office employee, † and the value of his summaries is specially mentioned by Manley (1953).Initially, Britton did not know the author of the meteorological information.In the 'separate file' (Figure 2; Britton, 1927), he described his good fortune in meeting Major Charles J. Fisher of Stroud, whose grandfather Paul Hawkins Fisher had written 'Notes and Recollections of Stroud'.Major Fisher suggested Britton consulted P.H. Fisher's book. In this, Fisher (1891) reported that Hughes: "kept a common place day book, in the form of loose sheets of paper, arranged alphabetically; in which he regularly entered notes of his doing, and made excerpts from the books he perused", Interpreting this with the medical references in the diaries, Britton (1927) concluded that the diarist was likely to be Thomas Hughes.In the 1891 second edition of Fisher's book consulted by Britton, the character of the diary entries is not discussed, beyond the implication that it was for his professional medical matters.However, in a recently discovered first edition ‡ of Notes and Recollections of Stroud (Fisher, 1871), Fisher's original text explicitly declared that Hughes: "kept a register of the rain-water that fell in the year; for the gauging of which he contrived an apparatus at the top of his house".This additional material was not carried forward to the second edition of Fisher's memoir (Fisher, 1891).It is important, as it identifies Hughes as the weather diarist beyond doubt.
2.2 | Recording and site considerations Britton (1927) concluded that the entries for 1771 and 1772 were from different sites, which he suspected were on the outskirts of Stroud.Closer inspection of Hughes' diaries, combined with new biographical information (summarised in the Appendix), indicates that entries in the first 2 years of the diary, 1771 and 1772, were made elsewhere; for the 21 August 1773, there is an entry 'at Stroud' and then in 1774 'removed to Stroud'.The specific location of the early observations is not known.The diaries state that Hughes moved to Stroud in 1774, only setting up his instruments to be ready for January 1775.The record for Stroud therefore begins in 1775, but some of the other information, such as the auroral data and to some extent rain, snow and thunder, is relatively independent of the exact site.
The original pages of the diary were arranged to form one month of records per page.At the end of a year, the sheets were folded down the centre.On the few occasions when Hughes was absent, the measurements were recorded in a different hand.§ There is no previous indication of Hughes' interest in recording weather, but when the diary began on the 1 January 1771, it was sufficiently well constructed that it could be continued in a very similar format for the following 40 years until just before his death in 1813, the only break being the full year of 1774 during which he moved to Stroud.
Hughes' 'observatory' was a chemist's shop ‖ on the north-facing side of the High Street in the centre of Stroud (51.43°N 2.26°W).Stroud lies at the confluence of five valleys, two of which lie in a generally northerly direction and two others lie more or less east-west.The town centre lies on the southern side of the east-west valley, and to the north, there is an arc of hills with the highest points being 271 m at 4.8 km to the north-west, 283 m at 7.2 km to the north, 272 m at 7.7 km to the north-east, and continuing at around 250 m or more to the east and closer to the town.None of the intervening land between these high points has an altitude below 170 m, and much of it is in fact higher.Thus, the view in the north-west to north-east arc from Thomas Hughes' vantage point at nominally 73.7 m was severely restricted to 2-3 km, because of the surrounding hills: there would have been no visibility down the southward valley from the site of Hughes' house.
An obvious consequence of Hughes' professional work was that his observations were restricted to times when he was at home, and consequently events may have been missed.

| CLIMATOLOGICAL ANALYSES
Britton summarized the diary information and climatological data in a short unpublished manuscript (Britton, 1927), kept with the diary (Figure 2).His summary was compiled from Hughes' daily ¶ records of the meteorological measurements together with comments about both weather and, where applicable, seasonal and medical comments.Britton considered extracting fog days but did not see value in providing a summary, as the definition applied to haze, mist and fog appeared quite variable.Further, Britton did provide a table of days of hail, but these are not extracted here as the use of thunder days, with which there is an overlap, is much more valuable.Britton's monthly data for rainfall amount and rain days, surface pressure, snow days, thunderstorm days and auroral nights are provided here as data tables, available in the University of Reading Research Data Archive at http://dx.doi.org/10.17864/1947.234.In these tables, values thought questionable by Britton are shown in italics, such as when there were fewer than 20 values from which to derive monthly mean values: the ‖ Hughes' final home in Stroud, at 57 High Street, which he occupied after living in 56 High Street, has long remained a pharmacy and continues to house one.¶ Hughes' diary entries were occasionally made more frequently than daily.
For example, in July 1793 he made multiple temperature measurements during the afternoons, no doubt to ascertain the maximum value.original use by Britton of both zeros and blanks in the tables has been retained, as it is not clear in some cases whether a blank should be interpreted as nothing was observed or nothing was recorded.Summary statistics are given across all available data, although the first few years up to 1774 are for a different but probably nearby site in south Gloucestershire, perhaps at Hughes' former residences of Wotton-under-Edge (51.638°N 2.349°W) or Marshfield (51.462°N 2.317°W).In addition, some checks are applied to the data, presented in Figure 3.Because Hughes' data have had various use in other datasets, for example in filling in the Hornsby rainfall series for Oxford (Craddock and Craddock, 1977), care has been taken to avoid the possibility of circular comparison, and self-consistency checks devised.

| Rainfall amounts and rain days
Table 1 provides the monthly and annual rainfall amounts.The original data values provided by Britton were given in inches, and a conversion has been made to millimetres.The annual totals have been recalculated from the converted monthly values.The greatest annual rainfall was in 1799 and the least in 1788.Table 2 provides the distribution of rain days, defined as days on which at least 0.1 mm (0.005 inch) rain was recorded.September 1804 had no rain days, and December 1781 had the greatest number, 27.As a cross-check on the two sources of rain data, the monthly rainfall amounts have been plotted against the monthly rain days, and the two quantities are strongly correlated (Figure 3a).The frequency distribution of daily rainfall has also been found by combining the values from Tables 1 and 2 (Figure 3b).The median daily rainfall is 4.7mm, with an interquartile range of 2.6 mm.

| Surface barometric pressure
Table 3 provides the monthly surface pressure for months when there are 20 or more days' measurements available.Following Britton's analysis, the pressure values have been corrected for defective vacuum and reduced to mean sea level by adding 0.5 inches of mercury to the original measurements, before conversion to SI units using the factor of 33.8639 hPa/(inch Hg).Extreme daily values of sea level pressure identified by Britton (corrected and converted in the same way) were 1,050.1 hPa on 26 December 1778 and 961.1 hPa on 20 January 1791.These maximum and minimum values are corroborated by measurements of 1,047 hPa and 961 hPa, respectively, at London, on the same dates (Cornes et al., 2012).Figure 3c plots the monthly mean pressure against the monthly mean rainfall.It is clear from this that there is negligible rainfall when the pressure is high and the greatest rainfall when the pressure is low, which provides a consistency check on the values tabulated.| 11 HARRISON ANd HARRISON

| Snow days
The monthly totals of days on which snow fell are provided in Table 4. Britton remarks that Hughes made a marginal note on the 11 June 1791 that 'Snow was said to fall upon hills', but this event was disregarded from the tabulation as only from a secondary source.The greatest number of snow days was 13 in March 1789.As a check on the snow day data, totals for each winter (December-January-February) were made and compared with the Central England Temperature (CET) for the same year, averaged across the same months.Figure 3d shows the values obtained.It is apparent that the winter total of snow days increases with decreasing CET; that is there are more snow days in colder winters.Dividing the data at the median values and constructing a contingency table, the Fisher exact test rejects the null hypothesis of a unit odds ratio with p =0 .003.

| Thunderstorm days
The monthly totals of days with thunder or lightning (as defined by Britton, so this potentially includes the possibility of distant lightning with inaudible thunder) are presented in Table 5.These values can be compared with the rain days and are generally smaller.As a test of the thunderstorm day data, the monthly thunderstorm days have been compared with the CET. Figure 3e shows this comparison for the June data.Again, by dividing the data at the median values and constructing a contingency table, the Fisher exact test marginally rejects the null hypothesis of a unit odds ratio at a confidence level of 95%.

| Auroral nights
Despite the limited view of the northern horizon, there are 69 Aurora Borealis sightings recorded in the diaries between 1771 and 1809 (identified by a marginal note of 'AB') which have been shown to agree with other international records of aurora sightings on the same dates (Harrison, 2005).Table 6 provides the auroral data as monthly totals.These are plotted against annual sunspot numbers in Figure 3f.Constructing a contingency table by splitting the data at the median, the Fisher exact test rejects a unit odds ratio with p =0 .002.

| CONCLUSION
The long series of measurements for Stroud and south Gloucestershire has previously been recognised for its meteorological value, particularly concerning rainfall and temperature.However, the diary contains broader geophysical information which has largely been neglected until recently.Of these, the monthly thunderstorm days and auroral night summaries are probably the most useful, which are presented here together with previously unpublished monthly summaries of rain, snow and surface pressure.Investigations of the data suggest consistency between the different quantities, and with external contemporary records of the Central England Temperature and Sunspot number.
Recent historical research confirms the long-held assumption that anonymous weather diarist was indeed Thomas Hughes.It also provides some confidence that the earlier records (1771-1774) were obtained in south Gloucestershire, prior to the records beginning in Stroud in 1775.The consistent series of meteorological measurements and geophysical observations available is in part due to the combination of education and stable employment circumstances for an apothecary of the time.In addition, the medical network in which Hughes worked may well have provided additional necessary scientific training, formalism and structure.The consequence is a rare meteorological and geophysical dataset from the southern UK providing reliable information for part of the Dalton Minimum in solar activity.

ACKNOWLEDGEMENTS
The second author, Barry Harrison, died suddenly during the preparation of this paper in 2019, aged eighty.He was a businessman and engineer with a lifelong interest in meteorology and a Stroud resident for almost sixty years.He actively researched Stroud's scientists, enthusiastically disseminating his discoveries through invited talks at local societies and organizations.Hughes' diaries themselves belong to the Royal Meteorological Society, kept in the National Meteorological Archive: material from the diary is reproduced with the permission of the Royal Meteorological Society.Help is also gratefully acknowledged in finding archive sources from Ian Mackintosh, Dr Jenner's House and Garden, Stroud Museum in the Park, the Royal College of Surgeons, the Royal College of Physicians, St Andrews' University Archives, Gloucestershire County Archives, the Gloucestershire Family History Society and the National Archive.Howard Beard helped with Figure A2.Tim Burt and a second anonymous reviewer are thanked for their comments which improved this manuscript.other ailments, including Hughes' own bouts of lumbago.He noted the incidence of 'cyder colic' in January 1789 as well as the lack of 'cyder' in 1783 and 1795.
Hughes' diary also reproduces notable events clearly obtained from other sources, especially theGentleman's Magazine, a monthly publication of social, scientific and newsworthy reports circulated in Europe and America.He subscribed to this magazine, and both his death and his second wife's death were mentioned in it (Anon, 1813b;Anon, 1833).† His broader interest in meteorology is apparent from his inclusion in his diary of what now might be termed 'extreme weather' occurrences, originally reported in the magazine.
It can only be speculated as to why this diligent observer of the natural world kept the weather diaries, what had excited his initial interest, and what ideas he had as to how the conditions varied and the possibility of foretelling weather.However, there can be few men or women with a compelling hobby, not at all promoted in their own lifetime, whose activities somehow became more significant some 200 years later.It is therefore very fortunate that Thomas Hughes' diaries have survived.† Thomas Hughes' widow became the second wife of his medical partner, Dr W.W. Darke.
‡ This 1871 edition only emerged in April 2015, following an auction.It is kept by the Stroud Museum in the Park.§ Only one name is specifically mentioned in the whole diary, in Dec 1771: 'Jas Cooper who kept the records this week when I was indisposed'.A possible candidate for this temporary observer is Hughes' cousin, John, of Wotton-under Edge, who had the surname Cooper.An alternative is a James Cooper, son of Thomas and Frances Cooper, who was baptized in Wotton-under-Edge on 27 November 1749.
Tests of Hughes' data.(a) Monthly mean rainfall plotted against monthly rain days.(b) Histogram of daily rainfall, from dividing monthly rainfall by monthly rain days.(c) Monthly mean rainfall plotted against monthly mean pressure.(d) Total winter (December-January-February) snow days plotted against the DJF Central England Temperature (CET).(e) Thunderstorm days in June plotted against the June CET.(f) Annual auroral nights plotted against annual sunspot number.(In [d], [e] and [f], dashed grey lines mark the median values)