Nephosthe weather behind the paintings
Skaters crowd a frozen river beside a stepped-gable house with a red and white fence, a pink windmill and an iceboat, with Amsterdam’s church towers on the horizon.
Adam van Breen, Skating on the Frozen Amstel River, 1611. Oil on panel, 44.3 × 66.5 cm. The Lee and Juliet Folger Fund, in honor of Arthur K. Wheelock, Jr., 2010.20.1. Courtesy National Gallery of Art, Washington. CC0.

A study against the weather record

Adam van Breen

Skating on the Frozen Amstel River

1611 · Oil on panel, 44.3 × 66.5 cm · National Gallery of Art, Washington, 2010.20.1 · The Lee and Juliet Folger Fund

Van Breen painted “16011”, read as 1611, on the gable of this house portrait on the ice. Do the Low Countries winter records around that year show the severe winters the NGA links to skating scenes?

6of 9 on KNMI’s documentary scale for the winter of 1610–11: “Cold”, one step below “Severe”. Compiled evidence for the Low Countries, not an observation on the Amstel.

Chilly winters around 1611Painted day unknown

The recordsThe painting at NGA

The Nephos method

How this study was read

The method in full

  1. What is written

    Dated “16011” on the gable of the house, read by NGA as 1611. The catalogue identifies the Amstel just south of Amsterdam and links skating scenes to severe winters; an NGA article places the panel amid chilly winters. The date fixes the making, not the winter shown.

  2. Records of those days

    Not found or not yet searched

    • No thermometer or daily register for Amsterdam in 1610–11 has been found; KNMI’s inventory of Dutch instrumental series starts at the end of the 17th century.
    • No source consulted records ice on the Amstel in a particular week of 1610–11, or dates any session on the panel.
    • Buisman’s descriptive volume for 1575–1700 and the Landsman articles were not consulted; the NGA systematic catalogue entry was.

  3. Each claim tested

    • Were the winters on either side of the date severe? No. KNMI classes 1610–11 and 1611–12 as 6, “Cold”, one step below “Severe”. The last “Very severe” winter before the date was 1607–08.
    • Was the panel made amid a sequence of chilly winters? Yes in this classification: 3 consecutive winters, 1609–10 to 1611–12, are category 6 or colder.
    • Was 1646 colder still? The winter ending in 1646 is 7, “Severe”, one step above 1610–11. The winter that began late in 1646 returns to 6.
    • Did severe winters recur in the first half of the century? 9 of 50 winters in 1601–1650 are “Severe” or harsher, against 16 of 50 in 1651–1700. None in 1601–1650 is milder than “Fairly mild”.
    • What did one observer count? Fabricius’s diary gives 58 frost days for 1610–11, rank 12 of 19 winters, most first; January 1611 alone had 22.

  4. Verdict

    The reconstruction supports a run of chilly winters around the date, as the NGA article says, and a frost spell from late December 1610 into January 1611 in East Frisia. It does not show a severe winter in 1611, and nothing dates the ice in the picture.

    • Partially agreesA sequence of chilly winters around 1611 Three consecutive “Cold” winters in a regional documentary reconstruction; not an observation at Amsterdam.
    • Partially agreesA series of severe winters behind skating scenes Severe winters recur in 1601–1650, but more fall in 1651–1700; weather records cannot test why the scenes sold.
    • UnknownThe painted day and the Amstel’s ice The date fixes the making of the panel. No record links the scene to a particular winter or week.

What this cannot tell you. KNMI C_win: a nine-step documentary classification of the November–March season for the Low Countries, from 1 (extremely mild) to 9 (extremely severe). It is compiled evidence, not an observation at Amsterdam. The classification divides the 284 instrumental winters of 1707–1990 symmetrically around 5; its printed frequencies are reproduced by the file’s own 1707–1990 rows. The reference period itself lies largely within the Little Ice Age. Fabricius frost days are Lenke’s counts from a written diary, including days inferred within frost spells; they are not thermometer readings. The Lenke pages consulted do not state whether diary dates were converted between calendars. A ten-day Julian offset would move the 23 December–26 January spell to about 2 January–5 February. Lenke counts are from Osteel, East Frisia, about 205 km from Amsterdam, and they contributed to the KNMI estimates for 1591–1613. The NGA entry suggests the Zuiderkerk tower may have been revised after its spire was added in 1614, so work on the panel may not be confined to 1611.

Step 1 · The picture and its making

A house portrait on the ice

Van Breen fills the frozen Amstel with fashionable skaters, a boy on a push sled, an orphan with a colf stick and an iceboat under sail. In the NGA catalogue Alexandra Libby identifies the site: the river just south of Amsterdam, with the Nieuwe Kerk, the Oude Kerk and the new Zuiderkerk on the horizon. The mill at right matches a sawmill on Cornelis Danckertsz de Rij’s 1629 map. The house at left, with its stepped gable and painted fence, is identified as the Borssenburg estate. Its owner, the gunpowder maker Abraham Verbeeck, probably commissioned the picture as a portrait of his house in a festive winter setting.

The entry reads the weather in the panel as part of its subject: a bright winter day, with wind carrying chimney smoke, lifting flags and filling the iceboat’s sail. It also calls the house a character in a “carefully orchestrated composition”. The technical summary records reserves left for sections of the house, the windmill and the bridge, so these were planned before the surrounding paint was laid in. Nephos reads it as a studio composition built around a real place, not a record of one afternoon.

“on gable of manor house: 16011”

NGA object record, Inscriptions

“there is no reason to doubt that the painting’s date is 1611”

Libby (2017), note 3, on the unusual “0” inside the date

What the date fixes. A signature date dates the making of the panel, not the winter it shows. The calendar year 1611 touches two winters: November 1610 to March 1611, and the season that began in November 1611. The scene could also draw on earlier winters, on drawings or on the conventions of the genre. The entry adds a further caution: the blue of the Zuiderkerk tower may be a revision made after the spire was added in 1614. Van Breen also dated a second ice scene 1611, now in the Rijksmuseum, signed on an iceboat’s flag. The study therefore asks about the winters around the date. It does not ask which day is shown.

Step 2 · The Low Countries reconstruction

Cold winters around the date, but not severe ones

The record here is KNMI’s winter series for the Low Countries, gathered by J. Buisman and described by A. F. V. van Engelen, Buisman and F. IJnsen. It is compiled evidence, not an observation on the Amstel. Their 2001 chapter explains how each November–March season was scored on three aspects (temperature, duration and intensity of frost) from historical descriptions, then placed in one of nine categories. The categories are defined from the 284 instrumental winters of 1707–1990. For 1591–1613 the chapter lists Fabricius’s East Frisian frost counts among the contributing series.

The winter of 1610–11 is category 6, “Cold”, one step below “Severe”. So is 1611–12. Together with 1609–10 they make 3 consecutive “Cold” winters. The last “Very severe” winter before the date was 1607–08; the next “Severe” one came in 1617–18.

KNMI winter categories for the Low Countries, winters 1594–95 to 1649–50One bar per November–March season, labelled by the year of its January. Height is the documentary category from 1, extremely mild, to 9, extremely severe. Dark bars are severe or harsher, blue bars cold. Flags mark the two winters touching 1611 and the winter ending in 1646. Every value is in the table below.1 · Extremely mild2 · Very mild3 · Mild4 · Fairly mild5 · Normal6 · Cold7 · Severe8 · Very severe9 · Extremely severeWinter 1594–95: category 8, Very severeWinter 1595–96: category 5, NormalWinter 1596–97: category 5, NormalWinter 1597–98: category 6, ColdWinter 1598–99: category 6, ColdWinter 1599–00: category 7, Severe1600Winter 1600–01: category 7, SevereWinter 1601–02: category 6, ColdWinter 1602–03: category 6, ColdWinter 1603–04: category 5, NormalWinter 1604–05: category 4, Fairly mildWinter 1605–06: category 5, NormalWinter 1606–07: category 4, Fairly mildWinter 1607–08: category 8, Very severeWinter 1608–09: category 4, Fairly mildWinter 1609–10: category 6, Cold1610Winter 1610–11: category 6, ColdDated 1611Winter 1611–12: category 6, ColdWinter 1612–13: category 4, Fairly mildWinter 1613–14: category 6, ColdWinter 1614–15: category 6, ColdWinter 1615–16: category 6, ColdWinter 1616–17: category 4, Fairly mildWinter 1617–18: category 7, SevereWinter 1618–19: category 5, NormalWinter 1619–20: category 7, Severe1620Winter 1620–21: category 8, Very severeWinter 1621–22: category 6, ColdWinter 1622–23: category 5, NormalWinter 1623–24: category 7, SevereWinter 1624–25: category 5, NormalWinter 1625–26: category 5, NormalWinter 1626–27: category 6, ColdWinter 1627–28: category 5, NormalWinter 1628–29: category 4, Fairly mildWinter 1629–30: category 4, Fairly mild1630Winter 1630–31: category 5, NormalWinter 1631–32: category 4, Fairly mildWinter 1632–33: category 4, Fairly mildWinter 1633–34: category 6, ColdWinter 1634–35: category 7, SevereWinter 1635–36: category 5, NormalWinter 1636–37: category 5, NormalWinter 1637–38: category 6, ColdWinter 1638–39: category 5, NormalWinter 1639–40: category 5, Normal1640Winter 1640–41: category 6, ColdWinter 1641–42: category 4, Fairly mildWinter 1642–43: category 5, NormalWinter 1643–44: category 6, ColdWinter 1644–45: category 6, ColdWinter 1645–46: category 7, SevereVan Goyen, 1646Winter 1646–47: category 6, ColdWinter 1647–48: category 4, Fairly mildWinter 1648–49: category 7, SevereWinter 1649–50: category 5, Normal1650Year of each winter’s January
Each bar is one November–March season in the Low Countries, labelled by the year of its January. Categories follow Table 2 of van Engelen, Buisman and IJnsen (2001). These are documentary judgements for a region, not measurements at the painted site.

Testing the NGA’s statements. Dagomar Degroot’s 2023 NGA article says Van Breen painted “amid a sequence of chilly winters in the Low Countries”. The reconstruction supports that wording: the run of “Cold” winters is there. He adds that in 1646, when Van Goyen painted his NGA ice scene, “winter was even colder”. The Van Goyen panel is dated 1646 on a boat. The winter ending in 1646 is category 7, “Severe”, one step colder; the season that began late in 1646 returns to 6.

The catalogue entry explains the popularity of skating scenes as “likely in part due to a series of severe winters in the Low Countries”. Severe winters did recur: 9 of the 50 winters in 1601–1650 are “Severe” or harsher, and none is milder than “Fairly mild”. But the next half-century has more: 16 of 50. If the genre was strongest in the first half of the century, its popularity did not simply follow the count of severe winters. Weather records cannot test why buyers wanted these pictures.

Winters by category, counted from the KNMI file. Severe or harsher is 7–9; mild or milder is 1–3. Thermometer rows use De Bilt frost indices.
WintersBasisCountSevere or harsherCold (6)Mild or milderMean category
1551–1600Documents50111525.62
1601–1650Documents5091605.50
1651–1700Documents50161345.72
1707–1990Thermometers2844462455.00
1951–2000Thermometers5059164.34

The 1707–1990 row is the classification’s own reference. Its counts reproduce the chapter’s printed frequencies, a check on how the file is read. That reference period is itself largely within the Little Ice Age, so “Normal” here is not a modern normal. Rows before 1707 rest on documents; later rows rest on thermometer-based frost indices. The change of evidence is a limit on every comparison across 1700.

Every winter in the chart, with the line as stored in the KNMI file
WinterCategoryDefinitionKNMI file line (year, winter, summer, winter °C, summer °C, year °C)
1594–958Very severe1595, 8, 5, -16, 160, 75
1595–965Normal1596, 5, 4, 20, 156, 88
1596–975Normal1597, 5, 3, 20, 153, 86
1597–986Cold1598, 6, 5, 16, 163, 89
1598–996Cold1599, 6, 6, 12, 167, 90
1599–007Severe1600, 7, 3, 1, 151, 77
1600–017Severe1601, 7, 4, -14, 155, 74
1601–026Cold1602, 6, 5, 12, 163, 88
1602–036Cold1603, 6, 6, 8, 166, 88
1603–045Normal1604, 5, 6, 20, 168, 94
1604–054Fairly mild1605, 4, 5, 29, 160, 93
1605–065Normal1606, 5, 4, 23, 155, 89
1606–074Fairly mild1607, 4, 5, 38, 162, 98
1607–088Very severe1608, 8, 4, -20, 159, 73
1608–094Fairly mild1609, 4, 5, 38, 160, 97
1609–106Cold1610, 6, 5, 14, 164, 89
1610–116Cold1611, 6, 5, 14, 162, 88
1611–126Cold1612, 6, 5, 7, 164, 86
1612–134Fairly mild1613, 4, 5, 30, 161, 94
1613–146Cold1614, 6, 3, 12, 150, 81
1614–156Cold1615, 6, 6, 12, 169, 91
1615–166Cold1616, 6, 7, 11, 173, 93
1616–174Fairly mild1617, 4, 3, 38, 152, 93
1617–187Severe1618, 7, 3, 1, 150, 77
1618–195Normal1619, 5, 5, 26, 161, 92
1619–207Severe1620, 7, 5, 2, 160, 82
1620–218Very severe1621, 8, 2, -18, 145, 67
1621–226Cold1622, 6, 4, 12, 158, 85
1622–235Normal1623, 5, 6, 18, 166, 92
1623–247Severe1624, 7, 7, 2, 172, 88
1624–255Normal1625, 5, 4, 18, 158, 87
1625–265Normal1626, 5, 4, 23, 159, 90
1626–276Cold1627, 6, 3, 15, 148, 82
1627–285Normal1628, 5, 1, 19, 140, 79
1628–294Fairly mild1629, 4, 7, 29, 173, 100
1629–304Fairly mild1630, 4, 6, 36, 169, 101
1630–315Normal1631, 5, 7, 24, 173, 98
1631–324Fairly mild1632, 4, 4, 36, 158, 95
1632–334Fairly mild1633, 4, 4, 30, 154, 91
1633–346Cold1634, 6, 5, 5, 160, 84
1634–357Severe1635, 7, 6, -2, 167, 84
1635–365Normal1636, 5, 7, 21, 172, 96
1636–375Normal1637, 5, 7, 27, 175, 100
1637–386Cold1638, 6, 6, 10, 169, 90
1638–395Normal1639, 5, 5, 28, 162, 94
1639–405Normal1640, 5, 5, 17, 162, 89
1640–416Cold1641, 6, 5, 15, 161, 88
1641–424Fairly mild1642, 4, 4, 28, 158, 92
1642–435Normal1643, 5, 5, 26, 164, 94
1643–446Cold1644, 6, 6, 12, 169, 91
1644–456Cold1645, 6, 6, 16, 169, 92
1645–467Severe1646, 7, 7, 1, 171, 87
1646–476Cold1647, 6, 5, 12, 164, 88
1647–484Fairly mild1648, 4, 4, 35, 155, 93
1648–497Severe1649, 7, 3, 3, 152, 79
1649–505Normal1650, 5, 4, 26, 154, 89

The temperature columns are the reconstruction’s estimates, stored without a decimal point; they are not used on this page.

Step 3 · One observer’s winter

A month of frost in East Frisia

The daily weather notes used here are not Dutch. The pastor and astronomer David Fabricius kept a diary at Osteel in East Frisia, about 205 km north-east of Amsterdam. Walter Lenke’s 1968 study for the German weather service counted its frost days month by month. These counts come from written remarks, including days Lenke judged frosty within a frost spell. They are not thermometer readings.

Lenke’s account of the diary has frost from 23 December 1610 to 26 January 1611, broken only by rain on 3 January and 12–14 January, with snow several times. January 1611 has 22 frost days, against a 1593–1612 January mean of 13.3. Only January 1608 has more; 1599 has the same. Milder weather set in on 27 January, and February has 6, fewer than 17 of the 20 Februaries.

“das seit dem 23. XII. andauernde Frostwetter”

the frost weather lasting since 23 December

Lenke (1968), p. 27, on January 1611 in Fabricius’s diary. Translation by Nephos.
Frost days at Osteel by month, October 1610 to April 1611, beside the 1593–1612 monthly meansDark bars are Lenke’s counts of frost days in Fabricius’s diary for each month of the winter 1610–11. Pale bars are Lenke’s printed means for the same month in 1593–1612. January 1611 has 22 frost days against a mean of 13.3; February has 6 against 15.6.0510152025frost daysOctober 1610: 4 frost daysOctober mean, 1593–1612: 3.34October 1610November 1610: 5 frost daysNovember mean, 1593–1612: 6.55November 1610December 1610: 14 frost daysDecember mean, 1593–1612: 14.414December 1610January 1611: 22 frost daysJanuary mean, 1593–1612: 13.322January 1611February 1611: 6 frost daysFebruary mean, 1593–1612: 15.66February 1611March 1611: 2 frost daysMarch mean, 1593–1612: 10.82March 1611April 1611: 5 frost daysApril mean, 1593–1612: 3.35April 1611
Frost days are Lenke’s counts from the diary (Tab. 5 c). The pale bars are his printed means for 1593–1612. The pages consulted do not say whether dates were converted between the Julian and Gregorian calendars; a ten-day offset would move the frost spell to about 2 January–5 February 1611.

Over the whole winter the diary gives 58 frost days, rank 12 of 19 winters, most first, tied with 1601–02. The median is 69. The winter after the date had 80; 1607–08 had 96. So the diary shows a hard January inside an otherwise moderate winter.

Four winters as Lenke tabulated them, beside the KNMI category. Pilgram and Easton are earlier compilations cited by Lenke.
WinterFabricius frost daysPilgramEastonKNMI
1607–08961608 ungemein kalter WinterGrand Hiver8 · Very severe
1609–1070—normal pl. froid6 · Cold
1610–11581611 kalter Wintertiède6 · Cold
1611–12801612 kalter Winternormal pl. froid6 · Cold

The compilations do not agree on 1610–11. Pilgram calls 1611 a cold winter, Easton “tiède” (lukewarm), and KNMI “Cold”. KNMI used Fabricius’s counts for these years, so the diary is not an independent check on its category.

All 19 winters in Lenke’s table
WinterFrost daysPilgramEastonKNMI
1593–94471594 sehr kalter Winter (1595?)normal5 · Normal
1594–9588—très rigoureux8 · Very severe
1595–9653—tiède5 · Normal
1596–9760—normal5 · Normal
1597–9872—normal pl. froid6 · Cold
1598–99691599 kalter Winter (1600?)normal6 · Cold
1599–0086—froid7 · Severe
1600–01991601 große Kältenormal (!!)7 · Severe
1601–0258—tiède6 · Cold
1602–03791603 große Kältefroid6 · Cold
1603–04751604 langer und strenger Wintertiède5 · Normal
1604–0547—normal4 · Fairly mild
1605–06551606 kalter Winterfroid5 · Normal
1606–0735—tiède4 · Fairly mild
1607–08961608 ungemein kalter WinterGrand Hiver8 · Very severe
1608–0938—doux4 · Fairly mild
1609–1070—normal pl. froid6 · Cold
1610–11581611 kalter Wintertiède6 · Cold
1611–12801612 kalter Winternormal pl. froid6 · Cold

Each printed winter total equals the October–May cells of Lenke’s monthly table. One monthly row, 1594, sums to 71 against a printed 72; that year is not used here.

Step 4 · Where the records stop

Cold winters around the date; no day on the ice

The records support part of what the NGA has written. Around 1611 the Low Countries reconstruction has a run of “Cold” winters, as Degroot says. One observer in East Frisia logged a month of frost from late December 1610. Neither source shows a severe winter in 1610–11, and neither can say when the Amstel froze, how long the ice held, or what the sky was like over Borssenburg.

No instrumental record reaches back this far. KNMI’s inventory of early Dutch observations begins with a Leiden series of 1697–1698, and its first long series runs from 1706. No daily register for Amsterdam in 1610–11 was found. The next sources to read are Buisman’s descriptive volume for 1575–1700, cited by KNMI, and Rozemarijn Landsman’s 2011 article on Borssenburg. Neither was consulted for this study.

The panel’s bright day and brisk wind remain the painter’s choices within a commissioned composition. The records establish the kind of winters Van Breen lived through. They do not show that he painted any one of them.

Return to the painting at the National Gallery of Art

Sources

Every source on this page

Winter categories are read from the KNMI file and frost-day counts from a scan-checked transcription of Lenke’s tables, both tied to sha256 fingerprints. The NGA pages were saved as served inside a browser session, because direct requests return 403. Quoted phrases are checked against these texts. A fingerprint preserves the version used; it does not independently validate the historical interpretation.

  1. Alexandra Libby, “Skating on the Frozen Amstel River, 1611,” Dutch Paintings of the Seventeenth Century, NGA online edition (2017)Copyright NGA; brief quotation and paraphrase · retrieved 15 October 2026 · Entry, technical summary and notes 3 and 5; HTML as served, fetched inside a browser session because direct requests return 403sha256 c99c4560879c4e66db820a5a8d926bf372d5758b1d765e26e11b2d4173ffd19d
  2. National Gallery of Art, 2010.20.1: object recordMuseum text; brief quotation · retrieved 15 October 2026 · Inscriptions & Marks; Open Access statement; provenance; HTML fetched inside a browser sessionsha256 eb1371e4bbb3d54e4bb5e4ce7c7a2d59264a135e4b978e2b07c7c209ec4308b7
  3. National Gallery of Art, Open Access PolicyNGA policy text; public-domain images released under CC0 · retrieved 15 October 2026 · Open Access Policy sectionsha256 1f93fe7ce9cb282d15da0dc3473b69abfa47b0df8bf337d3f71896b050b0b7a0
  4. NGA, Skating on the Frozen Amstel River, 2010.20.1, 1600-pixel imageCC0; Courtesy National Gallery of Art, Washington · retrieved 15 October 2026 · IIIF derivative of the primary image listed in NGA open data (openaccess = 1)sha256 94b509721e8cfb809c42cb066d4842d89624fd9fc32d1fc4c56e86a01d2cbb55
  5. Dagomar Degroot, “Painting Climate Change in the 17th Century,” NGA, 10 April 2023Copyright NGA; brief quotation · retrieved 15 October 2026 · Paragraph on Van Breen and Van Goyen; HTML fetched inside a browser sessionsha256 df2c0497eef52a007afcc1a31cb374de034ede6636cf8a0228b3cbfd4c4f5371
  6. National Gallery of Art, 2014.35.1: Jan van Goyen, Ice Scene near a Wooden Observation TowerMuseum text; brief quotation · retrieved 15 October 2026 · Inscriptions & Markssha256 760909555469011717bc2f2cf6303fb628e472511d6baffe9a887cb128a9a3b8
  7. Rijksmuseum, SK-A-2510: Adam van Breen, Landscape with Frozen Canal, Skaters and an Ice-BoatMuseum record; brief quotation · retrieved 15 October 2026 · Inscriptions / markssha256 17f206c49329335802c085029f38ad95b082e1f513829544316416c6c4c283e6
  8. KNMI, Nederland winter-zomer 751–2000 (data gathered by J. Buisman; described by A. F. V. van Engelen, J. Buisman and F. IJnsen)Free use with acknowledgement of the Royal Netherlands Meteorological Institute (KNMI), per the file header · retrieved 15 October 2026 · nederland_wi_zo.dat, column C_winsha256 a5d97caee7d66ce417a41e50e763f203acb007b5774ff9c82fc55d7c2e934e03
  9. KNMI, Klimatologie: Antieke waarnemingenKNMI web page; cited · retrieved 15 October 2026 · Inventory of early Dutch instrumental series and the link to the winter-summer seriessha256 c6b0efdf7a398600cac08e4e80a113355ae3c1e10a7835c6e74a98e7ad604835
  10. van Engelen, Buisman and IJnsen, “A Millennium of Weather, Winds and Water in the Low Countries” (2001), KNMI copyCopyright publisher; KNMI-hosted scan; cited and briefly quoted · retrieved 15 October 2026 · Table 2 and pp. 6–8 (classification, contributing series); p. 21 (winter labelling)sha256 4e5f9fa5283870f5e289bd49cc89640f6382ce2b5830c637354bad57e70403f8
  11. Nephos transcription of Table 2 and method passages from the 2001 chapterNephos transcription; short excerpts of a copyright text · retrieved 15 October 2026 · Committed copy: window-engine/evidence/van-breen-frozen-amstel-1611/sha256 f274faad65f1533716f2b2c65af51078fe782db3081d90bf058e744142432b1f
  12. KNMI publication record for the 2001 chapterKNMI web page; cited · retrieved 15 October 2026 · Abstract and PDF linksha256 1ece1b42a2b4b3c04dfd0db90499b6191c72899765e048717cc299706c9503b4
  13. Walter Lenke, Das Klima Ende des 16. und Anfang des 17. Jahrhunderts … David Fabricius in Ostfriesland, Berichte des Deutschen Wetterdienstes 110 (1968)Deutscher Wetterdienst retro-digitized report; figures cited, short quotation · retrieved 15 October 2026 · pp. 8, 10–12 (observer, frost counting); p. 27 (winter 1610–11); p. 34 (Tab. 5 c, 5 d)sha256 3132f4239795a1bc2fa26de96dad20e0292c91200c452b8f6f391a121f90941d
  14. Lenke (1968), p. 27, text layer extracted with pdftotext 26.04.0Extraction for quotation checks · retrieved 15 October 2026 · Column order in the text layer is interleaved; the quoted phrase is contiguoussha256 baabd7dd819836ca1bfa50a4a958b4a82782f29605f00b4c2bcc8d95b008a31f
  15. Lenke (1968), pp. 7–12, text layer extracted with pdftotext 26.04.0Extraction for quotation checks · retrieved 15 October 2026 · Observation places and frost countingsha256 36d9edcbbefebb5c771772dc635df4158b15c3ac1129a7e64bfeb1e40ac97211
  16. Nephos transcription of Lenke’s Tab. 5 c and 5 d and the 1610–11 narrativeNephos transcription of published counts; short excerpts · retrieved 15 October 2026 · Committed copy: window-engine/evidence/van-breen-frozen-amstel-1611/sha256 4f651f3082a657ebbcaf54f72da966c54430161152d27bb83d7dabcb5372b4fe
  17. OpenStreetMap, Osteel (village boundary point)ODbL 1.0; © OpenStreetMap contributors · retrieved 15 October 2026 · Approximate village point, not Fabricius’s housesha256 90159f80837d14a3cac2ac6a38f5d4d5723a097a2e41d1235a2eabe5f1d95c71
  18. OpenStreetMap, Amsterdam (city point)ODbL 1.0; © OpenStreetMap contributors · retrieved 15 October 2026 · City point; the painted site lies on the Amstel south of the 1611 citysha256 a586872e21d51288d421bf3b8f4cf83b1d646a9175cae061e1d3c6ad132048e2

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