Nephosthe weather behind the paintings
Claude Monet, The Thames below Westminster: boats and a timber jetty in front of Westminster Bridge and the hazy Houses of Parliament.
Claude Monet, The Thames below Westminster, about 1871. Oil on canvas, 47 × 73 cm. National Gallery, London, NG6399. Public domain (PD-Art), via Wikimedia Commons.

A study against the weather record

Claude Monet

The Thames below Westminster

About 1871 · National Gallery, London, NG6399 · Bequeathed by Lord Astor of Hever, 1971

Monet gave the river a luminous haze and heightened Parliament’s towers. Do the records support fog and weaker winds during his first London stay?

29days with fog noted at Greenwich in January–May 1871, out of 151. No day can be assigned to the painting.

Meteorological context partly agreesAerosol amount unknown

The recordsThe painting at the National Gallery

The Nephos method

How this study was read

The method in full

  1. What is written

    The canvas is inscribed “Claude Monet 71”. The holder places Monet in London from September 1870 to May 1871; his letter from Zaandam establishes that he had left by 2 June. January–May is the dated-year segment; September–May supplies wider stay context. Neither identifies a painted day.

  2. Records of those days

    Not found or not yet searched

    • No verified painting session or daily smoke concentration is available.
    • Greenwich cannot establish the atmosphere along Monet’s Westminster sightline.
    • The original Daubigny letter was not inspected; its dated testimony is read through the National Gallery’s scholarly catalogue.

  3. Each claim tested

    • Were fog and weaker winds available during the dated year? January–May 1871 has 29 days with a fog notation out of 151. Median daily wind travel is 164 miles on those days and 271 on the others.
    • Does the broader stay give similar context? September–May has 86 fog-notation days out of 273; the corresponding medians are 154 and 289 miles. The month-by-month table retains the April exception.
    • Does this test the PNAS pollution trend or date the picture by the Sun? It supplies a meteorological consistency check only. Albright and Huybers study trends across works; Baker and Thornes study solar positions in the later Parliament series. Neither supplies a date or aerosol calibration for NG6399.

  4. Verdict

    The registers support recurring fog and an association with weaker daily wind during Monet’s stay. They do not determine how much of the painted haze was smoke, or which weather Monet painted.

    • Partially agreesMeteorological setting for the misty picture Compatible conditions recur at Greenwich; the match in place, hour and composition remains unproved.
    • UnknownPainted day and aerosol amount The necessary dated session and direct or calibrated pollution evidence are missing.

What this cannot tell you. A day with no fog code is not necessarily a clear day. A fog code says nothing about duration or chemical composition. Monthly humidity cannot be paired with individual painting sessions. Wind travel is an integrated historical instrument reading. The wind association is descriptive and may reflect season and other weather conditions. The page preserves all months and both date windows. The National Gallery identifies heightened Parliament towers and scumbled light; the painting is a constructed image, not an unaltered optical measurement.

Step 1 · The picture and its date

An observed river, a constructed atmosphere

The National Gallery describes a working Thames seen through haze. Monet scumbled the sky but used broken strokes for the water; he also heightened Parliament’s towers. Those choices matter: the image offers an interpretation of the atmosphere, not an unchanged optical record.

The catalogue says about 1871; the lower-right inscription reads “Claude Monet 71”. The holder places the London stay in September 1870–May 1871. Monet’s letter from Zaandam is dated 2 June 1871, confirming that he had left London by then. No dated painting session or detailed sequence of field and studio work has been established for this canvas.

Our narrower comparison uses January–May 1871, 151 calendar days: the overlap of the inscribed year with the documented stay. We also retain September–May as context for the whole stay. The first and last days are analysis boundaries, not known arrival, departure or painting dates.

“Zaandam ce 2 juin 71”

Monet to Pissarro, 2 June 1871; Zaans Museum French transcription, p. 2

Step 2 · Wind, fog and humidity

Fog often accompanied less wind travel

At Greenwich, roughly 8.7 km from Westminster Bridge, 29 of the 151 days in January–May carry a fog notation. Median daily wind travel is 164 miles on those days, compared with 271 miles on the 122 others. The Robinson anemometer recorded the movement of air over a whole day. A smaller total indicates weaker average wind at that instrument; it is not an instantaneous wind reading at Monet’s easel.

Across the broader September–May envelope, 86 of 273 days mention fog, with medians of 154 and 289 miles. The monthly medians retain an exception: in April, the 5 fog-notation days have a median of 272 miles, against 266 on the others. This is a descriptive association; season, observation time and other weather conditions can contribute to it.

The printed monthly Degree of Humidity ranges from 74 to 90, with saturation represented by 100. The observatory calculated these summaries using Glaisher’s hygrometrical tables. They describe moisture conditions across months, not humidity on a particular fog or painting day.

Median daily wind travel, with and without a fog notationPaired bars for each month of the London stay. Red is a day with a fog code; blue-grey is a day without one. Fog days have a lower median in every month except April. The complete figures and sample sizes follow in a table. These are Greenwich observations.Fog mentionedNo fog notation0100200300400500miles of wind travel per daySep 1870Sep 1870, Fog mentioned: 132.5 miles132.5Sep 1870, No fog notation: 278.5 miles278.5Oct 1870Oct 1870, Fog mentioned: 236 miles236Oct 1870, No fog notation: 427 miles427Nov 1870Nov 1870, Fog mentioned: 117 miles117Nov 1870, No fog notation: 371 miles371Dec 1870Dec 1870, Fog mentioned: 139 miles139Dec 1870, No fog notation: 274.5 miles274.5Jan 1871Jan 1871, Fog mentioned: 179 miles179Jan 1871, No fog notation: 254 miles254Feb 1871Feb 1871, Fog mentioned: 143 miles143Feb 1871, No fog notation: 329.5 miles329.5Mar 1871Mar 1871, Fog mentioned: 135 miles135Mar 1871, No fog notation: 351 miles351Apr 1871Apr 1871, Fog mentioned: 272 miles272Apr 1871, No fog notation: 266 miles266May 1871May 1871, Fog mentioned: 155 miles155May 1871, No fog notation: 235 miles235
Greenwich, September 1870–May 1871. Medians are calculated separately for each month and each group of days; there is no averaging across stations. A day without a fog code is not necessarily clear.
Every month: counts, wind medians and humidity
Wind medians in miles per civil day; humidity is the observatory’s monthly summary, saturation = 100.
MonthFog / daysWind: fogWind: otherHumidity
September 187012 / 30132.5278.583
October 187016 / 3123642785
November 187018 / 3011737190
December 187011 / 31139274.586
January 18719 / 3117925487
February 18714 / 28143329.586
March 187110 / 3113535179
April 18715 / 3027226683
May 18711 / 3115523574

Step 3 · Witness and scholarship

A consistency check for the pollution interpretation

A contemporary witness puts fog within the earlier stay. On 15 October 1870, Daubigny wrote to Rochenoire about having to light a candle in the morning. Sarah Herring’s National Gallery catalogue supplies the date and published transcription. This is testimony from London, not a visibility measurement at Westminster; the original letter has not been inspected.

Albright and Huybers (PNAS, 2023) relate changes in painted contrast to reconstructed annual sulphur-dioxide emissions, while accounting for year and subject matter. The article describes a Monet sample of early Paris-area works and later London paintings; this description places NG6399 outside those groups. We have not checked the underlying painting dataset. Their discussion also examines weak winds on documented painting days in 1900. Greenwich’s earlier record supports testing that meteorological pathway during the first stay. It cannot verify the paper’s long-term trend or establish that Monet selected the fog days counted here.

The JSTOR item is Baker and Thornes, Solar position within Monet’s Houses of Parliament (2006). Its repository abstract describes dating scenes in the later Parliament series from the Sun and architectural geometry, checked against letters from 1900. That is a model of documentary cross-checking, not a date for this earlier work. No equivalent solar constraint has been established here.

“Fog! Visibility less than two paces.”

Daubigny to Rochenoire, 15 October 1870; Herring (2019), note 19, citing Moreau-Nélaton (1925), p. 102

Step 4 · What survives the test

Weather context survives; aerosol amount does not

The records support the availability of recurring fog, moist months and weaker winds on many fog days. These are conditions relevant to the accumulation and optical effects of pollution. They do not identify how much smoke was present: the fog notation cannot separate water droplets, smoke particles and their mixture. Humidity is an indirect contextual indicator, not a substitute for a measurement of aerosol mass or optical depth.

The holder’s interpretation connects the haze with industrial London; the weather register is compatible with that setting. The painting’s scumbled light and altered architecture remain artistic choices. Without a painting session and evidence along the actual sightline, the records cannot tell us which atmospheric event he retained or changed.

The transcription counts f, sl.-f and th.-f as fog mentions. Haze, mist, frost and gloom alone are excluded. A code anywhere in the day counts once, without an assumed duration. Wind totals run midnight to midnight. All monthly wind sums match the printed totals; a single reader checked the scans, so an independent transcription audit remains advisable. No modern anomaly, exceptional-year rank or local pollution concentration is reported.

All daily wind readings and fog classifications
A positive row shows one verbatim fog token from that day. “No fog code” means none was found in the complete weather row.
Civil dateWind travel, milesFog token
1 September 1870288No fog code
2 September 1870387No fog code
3 September 1870273No fog code
4 September 1870246No fog code
5 September 1870400No fog code
6 September 1870203No fog code
7 September 1870214No fog code
8 September 1870404No fog code
9 September 1870485No fog code
10 September 1870632No fog code
11 September 1870143f
12 September 1870284No fog code
13 September 1870324No fog code
14 September 1870363No fog code
15 September 1870111th.-f
16 September 187087sl.-f
17 September 1870189sl.-f
18 September 187079No fog code
19 September 1870120No fog code
20 September 187086th.-f
21 September 187091f
22 September 1870145No fog code
23 September 1870225No fog code
24 September 1870161f
25 September 1870115th.-f
26 September 1870122th.-f
27 September 1870165th.-f
28 September 1870144f
29 September 1870159f
30 September 1870220No fog code
1 October 1870267th.-f
2 October 1870205No fog code
3 October 1870154f
4 October 187098f
5 October 187096f
6 October 187098th.-f
7 October 1870145sl.-f
8 October 1870427No fog code
9 October 1870331No fog code
10 October 1870292sl.-f
11 October 1870205sl.-f
12 October 1870536No fog code
13 October 1870690No fog code
14 October 1870148sl.-f
15 October 1870107sl.-f
16 October 1870486No fog code
17 October 1870423No fog code
18 October 1870297sl.-f
19 October 1870511No fog code
20 October 1870593No fog code
21 October 1870272No fog code
22 October 1870324No fog code
23 October 1870464No fog code
24 October 1870590No fog code
25 October 1870317sl.-f
26 October 1870298f
27 October 1870393No fog code
28 October 1870334f
29 October 1870331sl.-f
30 October 1870369f
31 October 1870323No fog code
1 November 1870291sl.-f
2 November 187089f
3 November 187058th.-f
4 November 1870104f
5 November 187090f
6 November 1870102th.-f
7 November 1870154f
8 November 1870103f
9 November 1870106th.-f
10 November 1870394No fog code
11 November 1870393No fog code
12 November 1870317No fog code
13 November 1870327f
14 November 1870335No fog code
15 November 1870260No fog code
16 November 1870238sl.-f
17 November 1870155f
18 November 1870189f
19 November 1870199f
20 November 1870253f
21 November 1870366No fog code
22 November 1870435No fog code
23 November 1870462No fog code
24 November 1870640No fog code
25 November 1870376No fog code
26 November 1870128sl.-f
27 November 187087f
28 November 1870100f
29 November 1870172No fog code
30 November 1870290No fog code
1 December 1870203No fog code
2 December 1870127f
3 December 1870314No fog code
4 December 1870282No fog code
5 December 1870124No fog code
6 December 1870147f
7 December 1870342No fog code
8 December 1870161sl.-f
9 December 1870139f
10 December 187097f
11 December 1870178No fog code
12 December 1870386No fog code
13 December 1870324No fog code
14 December 1870522No fog code
15 December 1870203No fog code
16 December 1870164No fog code
17 December 1870159f
18 December 1870437No fog code
19 December 1870565No fog code
20 December 1870370No fog code
21 December 1870452No fog code
22 December 1870267No fog code
23 December 1870169sl.-f
24 December 187086sl.-f
25 December 1870126th.-f
26 December 1870210sl.-f
27 December 1870243No fog code
28 December 1870204No fog code
29 December 1870209No fog code
30 December 1870165No fog code
31 December 1870126sl.-f
1 January 1871141No fog code
2 January 1871132No fog code
3 January 1871147No fog code
4 January 1871112No fog code
5 January 1871368f
6 January 1871315No fog code
7 January 1871440No fog code
8 January 1871290sl.-f
9 January 1871149No fog code
10 January 1871205No fog code
11 January 1871179f
12 January 1871164sl.-f
13 January 1871215No fog code
14 January 1871345No fog code
15 January 1871426No fog code
16 January 1871599No fog code
17 January 1871433No fog code
18 January 1871211No fog code
19 January 1871108f
20 January 1871201f
21 January 1871164sl.-f
22 January 1871228sl.-f
23 January 1871310No fog code
24 January 1871409No fog code
25 January 1871479No fog code
26 January 1871291No fog code
27 January 1871293No fog code
28 January 1871215No fog code
29 January 1871139sl.-f
30 January 1871127No fog code
31 January 1871217No fog code
1 February 1871144No fog code
2 February 1871113th.-f
3 February 1871202No fog code
4 February 1871181No fog code
5 February 1871465No fog code
6 February 1871488No fog code
7 February 1871195No fog code
8 February 1871323No fog code
9 February 1871420No fog code
10 February 1871365No fog code
11 February 1871291No fog code
12 February 1871351No fog code
13 February 1871166f
14 February 1871242No fog code
15 February 1871190No fog code
16 February 1871120sl.-f
17 February 1871314No fog code
18 February 1871429No fog code
19 February 1871450No fog code
20 February 1871589No fog code
21 February 1871286No fog code
22 February 1871251sl.-f
23 February 1871336No fog code
24 February 1871338No fog code
25 February 1871290No fog code
26 February 1871264No fog code
27 February 1871619No fog code
28 February 1871504No fog code
1 March 1871286No fog code
2 March 1871121No fog code
3 March 1871129f
4 March 1871260No fog code
5 March 1871381No fog code
6 March 1871370No fog code
7 March 1871420No fog code
8 March 1871583No fog code
9 March 1871527No fog code
10 March 1871318No fog code
11 March 1871448No fog code
12 March 1871491No fog code
13 March 1871449No fog code
14 March 1871262No fog code
15 March 1871257No fog code
16 March 1871422No fog code
17 March 1871199f
18 March 1871122sl.-f
19 March 187195f
20 March 1871107f
21 March 1871199sl.-f
22 March 1871141f
23 March 1871158f
24 March 1871123f
25 March 1871124No fog code
26 March 1871173No fog code
27 March 1871352No fog code
28 March 1871351No fog code
29 March 1871329No fog code
30 March 1871221No fog code
31 March 1871329f
1 April 1871173No fog code
2 April 1871272sl.-f
3 April 1871236No fog code
4 April 1871208No fog code
5 April 1871270No fog code
6 April 1871247No fog code
7 April 1871229No fog code
8 April 1871230No fog code
9 April 1871183No fog code
10 April 1871224No fog code
11 April 1871248No fog code
12 April 1871457No fog code
13 April 1871320No fog code
14 April 1871214sl.-f
15 April 1871466No fog code
16 April 1871476No fog code
17 April 1871290No fog code
18 April 1871217No fog code
19 April 1871397No fog code
20 April 1871420No fog code
21 April 1871284No fog code
22 April 1871353No fog code
23 April 1871401No fog code
24 April 1871126No fog code
25 April 1871151f
26 April 1871223No fog code
27 April 1871323sl.-f
28 April 1871358No fog code
29 April 1871266No fog code
30 April 1871289sl.-f
1 May 1871265No fog code
2 May 1871129No fog code
3 May 1871272No fog code
4 May 1871451No fog code
5 May 1871220No fog code
6 May 1871171No fog code
7 May 1871235No fog code
8 May 1871201No fog code
9 May 1871358No fog code
10 May 1871251No fog code
11 May 1871123No fog code
12 May 1871208No fog code
13 May 1871334No fog code
14 May 1871235No fog code
15 May 1871177No fog code
16 May 1871190No fog code
17 May 1871258No fog code
18 May 1871264No fog code
19 May 1871178No fog code
20 May 1871277No fog code
21 May 1871138No fog code
22 May 1871251No fog code
23 May 1871265No fog code
24 May 1871166No fog code
25 May 1871204No fog code
26 May 1871289No fog code
27 May 1871155sl.-f
28 May 1871360No fog code
29 May 1871284No fog code
30 May 1871139No fog code
31 May 1871205No fog code

Sources

Every source on this page

Each file was downloaded and given a fingerprint (its sha256). The page is rebuilt from these files and will not build if a fingerprint changes, so every number above comes from them rather than being typed in.

  1. Royal Observatory, Greenwich: observations for 1870Public-domain nineteenth-century government publication; BGS scan · retrieved 7 October 2026 · PDF pp. 147–154, printed lxviii–lxxv; daily wind and weather, monthly humiditysha256 b3f36953919e40426dfeb0146a26e78c8e299c82b2b8b7d3fee3c8b8e7c3c0fa
  2. Royal Observatory, Greenwich: observations for 1871Public-domain nineteenth-century government publication; BGS scan · retrieved 7 October 2026 · PDF pp. 121–130, printed xlvi–lv; introduction pp. liv–lv and lx–lxiisha256 cbc1a49982537d3b87572b186a57c8947dc92ce3e7c6e56ae26dc91d5bf15831
  3. Nephos transcription of the Greenwich registersNephos transcription of public-domain factual tables · retrieved 7 October 2026 · 273 daily rows and nine monthly humidity entries; individual page locators in JSON; one reader, not independent checkingsha256 108d4c95aa13ec0e8589f8a9e7f8eaacf41aeca3f8a291069bfe126d807dd249
  4. National Gallery, The Thames below Westminster, NG6399Copyright National Gallery; public research reference, short quotation and paraphrase only · retrieved 7 October 2026 · Object details, Overview and In-depthsha256 2e7e2857a367e63f960f34168d4dc8f7942cfbbfaaa9456db72653532f804c4b
  5. Text extraction of the National Gallery object pageCopyright National Gallery; research cache only · retrieved 7 October 2026 · HTML tags removed and whitespace normalized; no wording changessha256 d88be776987ebfb3aad5b77d97378b91db83ea4b2ea77520513b578c3b8b7bb5
  6. Monet to Pissarro, 2 June 1871: manuscript supplied by Zaans MuseumPublic-domain letter by Monet; museum-supplied research scan, not republished here · retrieved 7 October 2026 · PDF p. 1, right-hand leaf: dateline; all four PDF pages retainedsha256 ff14a159a29f9fea7278ec4947e4156b390167993dcc8fae1f92d25c33c71597
  7. Zaans Museum, transcription and translations of Monet’s letterHistorical French text public domain; modern translations © their owners, short extracts only · retrieved 7 October 2026 · PDF p. 2: French dateline and text; p. 3: English translationsha256 ee824ed2792e317c8dd79365a96c63f29ed199ca0d6c1f97366709c681f0658e
  8. Text extraction of the Zaans Museum transcriptionHistorical French text public domain; modern translations © their owners, research cache only · retrieved 7 October 2026 · PyMuPDF extraction of all three pagessha256 8c6cfdcaa67dbba0b4b5599647085e688160c8af31340cc70f75862d02e3d339
  9. Sarah Herring (2019), St Paul’s from the Surrey Side, National Gallery catalogueCopyright National Gallery; scholarly reference, short quotation only · retrieved 7 October 2026 · Discussion and note 19: Daubigny to Rochenoire, 15 October 1870; Moreau-Nélaton (1925), p. 102sha256 402969a4e6b1f52e4c154fd38335c7091170c3901931fcaa937276fdf96d9c99
  10. Text extraction of Sarah Herring’s catalogue entryCopyright National Gallery; research cache only · retrieved 7 October 2026 · HTML text and note 19, whitespace normalizedsha256 c3c66913c20843ade8664f053f48914aed2a6d832564aa959530a73cc44a3048
  11. Anna Lea Albright and Peter Huybers (2023), Paintings by Turner and Monet depict trends in 19th century air pollutionCC BY 4.0, authors; PNAS 120(6), e2219118120 · retrieved 7 October 2026 · Main article in full; Quantifying Historical Air Pollution, Results, Discussion, Conclusionssha256 3408771977b6f507f67d410f5af576fe6a9c1ebea4052d6a333f8de06185e05b
  12. Text extraction of the PNAS articleCC BY 4.0, authors · retrieved 7 October 2026 · HTML tags removed and whitespace normalizedsha256 a4213b921ee2280062943390f55a04ad94e86e64afb4408c5f3d1ce336bb53d9
  13. Jacob Baker and John E. Thornes (2006), Solar position within Monet’s Houses of ParliamentUniversity of Birmingham repository metadata and abstract; copyright authors/publisher · retrieved 7 October 2026 · Abstract and bibliographic metadata only; DOI 10.1098/rspa.2006.1754; JSTOR 20209098sha256 dd6a0f3db8fa15f0352d06004ec9d5a9690e0e625d2c74619667800913e9e2b9
  14. Text extraction of the Birmingham repository abstractCopyright authors/publisher; research cache only · retrieved 7 October 2026 · Full article not retrieved; no claim to have re-derived its geometrysha256 1e088d4067327ebb3a141e139098d7e143e9cd73618cba2367c16c87c0cc8674
  15. BGS, Greenwich observatory site coordinatesBGS/UKRI public factual metadata; no map reproduction · retrieved 7 October 2026 · 51° 29′ N, 0° 0′ E; rounded site position, not a surveyed instrument coordinatesha256 0d8ba52e5ff8886710a4bf25823461a12fb15deac885ee8cf18813ff0f75062f
  16. Text extraction of the BGS station pageBGS/UKRI public factual metadata · retrieved 7 October 2026 · Statistics: Geographic Coordinatessha256 a60cd7c137bfe3dca4936e91c5a597aecd80dc19d8a750c00198af544ed28da5
  17. OpenStreetMap, Westminster BridgeODbL 1.0, © OpenStreetMap contributors · retrieved 7 October 2026 · Bridge relation 19306462; distance reference only, not Monet’s exact easel positionsha256 f8e72817aee1796d7e789992cdca70869fae09898acfa05bebb53302d0fdc1c4
  18. Wikimedia Commons: image identity and PD-Art declarationCommons metadata CC BY-SA; work and faithful reproduction declared public domain · retrieved 7 October 2026 · NG6399; Monet died 1926; PD-Art / Public Domain Marksha256 5f0f5238c54b1e85a2bcbc0c56124845ca1c95d52fbb3c39acd678012d945edc
  19. Claude Monet, The Thames below Westminster, NG6399Public domain, PD-Art, per cached Wikimedia Commons file page · retrieved 7 October 2026 · 3000 × 1929 reproduction; lower-right inscription read as Claude Monet 71sha256 9c11fb708a97742365e41079311b2a99d931246815cc93c8b00d79275e7eb04e

The numbers on this page, as JSONThe method card, as JSON