Leibniz's Observations on Hydrology: An Unpublished Letter on the Great Lombardy Flood of 1705

Summary

Although the historical reputation of Gottfried Wilhelm Leibniz (1646–1716) largely rests on his philosophical and mathematical work, it is widely known that he made important contributions to many of the emerging but still inchoate branches of natural science of his day. Among the many scientific papers Leibniz published during his lifetime are ones on the nascent science we now know as hydrology. While Leibniz's other scientific work has become of increasing interest to scholars in recent years, his thinking about hydrology has been neglected, despite being relatively broad in extent, including as it does papers on the ‘raising of vapours’ and the formation of ice, as well as the separation of salt and fresh water. That list can now be extended still further following the discovery of a previously unpublished letter of Leibniz's on the causes of the devastating Lombardy flood of October and November 1705. This letter, which will be the focus of our paper, reveals the depth of Leibniz's understanding of key hydrological processes. In it, he considers various mechanisms for the flood, such as heavy rains on high ground, underwater earthquakes, and a mountain collapse. Over the course of the paper we examine each of these mechanisms in depth, and show that Leibniz was in the vanguard of hydrological thinking. We also show that the letter contains one of the first scholarly attempts to apply aspects of the still-forming notion of the hydrological cycle to account for a flood event.

Acknowledgements

The authors would like to thank two anonymous referees, as well as Stuart Elden, and Daniel J. Cook for their comments on an earlier draft of this paper; Eric Leinberger for construction of Figure 1; Matteo Salmetti for translating passages from the monograph of Daniele Salmelli; Nora Gaedeke and Charlotte Wahl for transcribing Leibniz's reading notes on Mariotte; and Sabine Sellschopp and Julia Weckend for assisting with the translation from old German of Leibniz's remarks on Palissy.

Notes

¹ G. W. Leibniz, ‘Protogaea’, Acta Eruditorum, (1693), 40–2. English translation in D. R. Oldroyd and J. B. Howes, ‘The first published version of Leibniz's Protogaea’, Journal of the Society for the Bibliography of Natural History, 9 (1978), 56–60.

² G. W. Leibniz, ‘Epistola ad autorem dissertationis de figuris animalium quae in lapidibus observantur, et Lithozoorum nomine venire possent’, Miscellanea Berolinensia, 1 (1710), 118–20; English translation in G. W. Leibniz, Shorter Leibniz Texts, translated and edited by Lloyd Strickland (London, 2006), 142–3. Also Leibniz's letter to Fontenelle published in Histoire de l'Académie Royale des Sciences, (1706), 9–11. Rhoda Rappaport has argued that this letter is in fact Fontenelle's abridgement of, and possibly commentary on, the no longer extant letter that Leibniz sent to Fontenelle, the Histoire's editor. However, the manuscript of Leibniz's handwritten draft of this letter to Fontenelle still exists in the Gottfried Wilhelm Leibniz Bibliothek, Hanover (shelf mark LBr 396 Bl. 128), and corresponds almost perfectly with the version published by Fontenelle, indicating that the Frenchman made no abridgements and few if any editorial changes to Leibniz's letter. See Rhoda Rappaport, ‘Leibniz on geology: A newly discovered text’, Studia Leibnitiana, 29 (1997), 6–11.

³ G. W. Leibniz, ‘Historia inventionis phosphori’, Miscellanea Berolinensia, 1 (1710), 91–8; English translation in Acta Germanica: Or the literary Memoirs of Germany, &c. Done from the Latin and High-Dutch by a society of gentlemen (London, 1742), 73–8.

⁴ G. W. Leibniz, ‘Meditatio de separatione salis & aqua dultis, novoque separationum chymicarum genere’, Acta eruditorum, 1 (1682), 386–8; English translation in Acta Germanica, 157–8.

⁵ See for example, Catherine Pécaut, ‘L'oeuvre géologique de Leibniz’, Revue générale des Sciences pures et appliqués, 58 (1951), 282–96; Jacques Roger, ‘Leibniz et la théorie de la terre’, in Leibniz 1646–1716. Aspects de l'homme et de l'oeuvre. Journées Leibniz, organisées au Centre International de Synthese les 28, 29 et 30 mai 1966 (Paris 1968), 137–44; Paolo Rossi, The Dark Abyss of Time: the History of the Earth and the History of Nations from Hooke to Vico (Chicago 1984); Roger Ariew, ‘A new science of geology in the seventeenth century?’ in Revolution and Continuity: Essays in the History and Philosophy of Early Modern Science, eds. Peter Barker and Roger Ariew (Washington: Catholic University of America Press, 1991), 81–92; E. P. Hamm, ‘Knowledge from underground: Leibniz mines the Enlightenment’, Earth Sciences History, 16 (1997), 77–99; Claudine Cohen, ‘Leibniz's Protogaea: Patronage, mining, and the evidence for a history of the Earth’, in Suzanne Marchand and Elizabeth Lunbeck (eds.), Proof and Persuasion: Essays on Authority, Objectivity, and Evidence (Turnhout, 1996), 124–43; Claudine Cohen, ‘An unpublished manuscript by Leibniz (1646–1716) on the nature of ‘fossil objects’’, Bulletin de la Société géologique de France, 169 (1998), 137–42; Stuart Elden, ‘Leibniz and geography: geologist, paleontologist, biologist, historian, political theorist and geopolitician’, Geographica Helvetica, 68 (2013), 81–93.

⁶ The only aspect that has not been ignored is Leibniz's debunking of the divining rod! See Warren Dym, Divining Science: Treasure Hunting and Earth Science in Early Modern Germany (Leiden, 2011), 162ff.

⁷ G. W. Leibniz, ‘De elevatione vaporum, & de corporibus quae ob cavitatem inclusam in äere natare possunt’, Miscellanea Berolinensia, 1 (1710), 123–8; English translation in Acta Germanica, 124–9.

⁸ G. W. Leibniz, ‘De la generation de la glace’, Mémoires pour l'histoire des sciences & des beaux-arts, (September 1701), 201–2.

⁹ P. Salvati, C. Bianchi, M. Rossi, and F. Guzzetti, ‘Societal landslide and flood risk in Italy’, Natural Hazards and Earth System Sciences 10 (2010), 465–83.

¹⁰ The following account is based on descriptions in Guido Alfani, ‘Climate, population and famine in Northern Italy: general tendencies and Malthusian crisis, ca. 1450-1800’, Annales de Démographie Historique 2 (2010), 41, and in Daniele Salmelli, ‘L'alluvione e il freddo: il 1705 e il 1709’, in R. Finzi, ed. Le meteore e il frumento: clima, agricoltura e meteorologia a Bologna nel 1700 (Bologna, Il Mulino, 1986), 17–97, especially 17–26.

¹¹ See for example Sophie's letters to Leibniz concerning the visions and apparent prophecies of Rosamund von der Asseburg, in G. W. Leibniz, Leibniz and the Two Sophies, translated and edited by Lloyd Strickland (Toronto, 2011), 69–74.

¹² Leibniz typically wrote his location at the end of his letters, and from this information we know that he was in Hanover at the time. See for example his letter to Electress Sophie of 31 October 1705, in Leibniz and the Two Sophies, 340.

¹³ Erik Amburger, ‘Einleitung’, in G. W. Leibniz, Sämtliche Schriften und Briefe, erste Reihe, fünfter Band, edited by Deutschen Akademie der Wissenschaften (Berlin, 1954), xxxix. The Sämtliche Schriften und Briefe is the critical edition of Leibniz's writings, in preparation since 1923. There are multiple volumes in eight series. Further references will identify the series number, then volume number, then page number.

¹⁴ Eckhart, ‘Lebensbeschreibung’, Journal zur Kunstgeschichte (1779), 159. Eckhart there records a story that had been oft-told by Leibniz, that during the crossing from Venice to Mesola the boat encountered a bad storm and the Italian crew, fearing for their lives, and believing that their German passenger could not understand them, discussed amongst themselves the possibility of lightening the load by throwing Leibniz overboard and dividing his belongings among themselves. The Lutheran Leibniz, who had overheard the conversation and had picked up enough Italian to understand what was going on, then pulled out a rosary that he had in his pocket and immediately implored God to protect the boat, whereupon the sailors abandoned their plan, believing that to kill a good Catholic, as Leibniz apparently was, would put their souls in jeopardy.

¹⁵ For details, see Amburger. ‘Einleitung’, xxxix-xl. For further information about Leibniz's Italian trip, see André Robinet, Iter Italicum (Mars 1689-Mars 1690) (Firenze, 1988).

¹⁶ G. W. Leibniz, Protogaea; sive, De prima facie telluris et antiquissimae historiae vestigiis in ipsis naturae monumentis dissertatio, edited by Christian Ludwig Scheidt (Göttingen, 1749). However, Leibniz did publish a summary of the work in 1693: G. W. Leibniz, ‘Protogaea’, Acta Eruditorum, (1693), 40–2.

¹⁷ See G. W. Leibniz, Protogaea, translated and edited by Claudine Cohen and Andre Wakefield (Chicago, 2008), 121–9.

¹⁸ Jacob Spon, Histoire de la Ville et de l'Estat de Geneve, depuis les premiers Siecles de la fondation de la Ville jusqu’à present, 2 vols (Lyon, 1682, 2nd ed): II, 239.

¹⁹ [Anon.], Strange and Terrible News, from Holland, and Yarmouth. Being a Perfect Relation, concerning the Inundation of the South Sea; And of its drowning the rich and populous City of Amsterdam; with divers other places in Friesland, Holland, Brabant, and Flanders, and the names of them (London, 1651), 2.

²⁰ [Anon.], A True Relation of the Great and Terrible Inundation of Waters, and over flowing of the Lower-Town of Deptford, on Thursday last, about two of the clock in the Afternoon (1651), 3.

²¹ [Anon.], A True Relation of the Great and Terrible Inundation of Waters, 4.

²² Thucydides, History of the Peloponnesian War, III.89. English translation from Thucydides, The Peloponnesian War, trans. Martin Hammond (Oxford, 2009), 174.

²³ ‘In eighty-nine [the year 1489] there was an earthquake in the sea of Atalia near Rhodes, which opened the sea, that is its bottom; and into this opening such a torrent of water was poured that for more than three hours the bed of the sea lay bare because of the water that had been lost from it; and then it closed to the former level’. Leonardo da Vinci, Notebooks (Oxford, 2008), 287.

²⁴ Jacob Spon (note 18): II, 141.

²⁵ [Anon.], Recit veritable et espouventable du tremblement de terre arrivé à la Pouille le 30 juillet de la presente année 1627. Traduit d'Italien en François, suyvant la lettre envoyée de Naples (le 7 août 1627) (Lyon, 1627), 11.

²⁶ As it happens, two significant earthquakes were reported in Italy in 1705, both land-based and located in the central Appenines; consequently, an associated tsunami is unlikely. Historic earthquakes in Italy: earthquake.usgs.gov/earthquakes/world/?region=Italy

²⁷ Reported in G. H. Eisbacher and J. J. Clague, Destructive Mass Movements in High Mountains: Hazard and Management (Ottawa, 1984), paper 84-16.

²⁸ Recorded on www.planat.ch/en/knowledge-base/chronicle/historical-events (Swiss National Platform for Natural Hazards). Farther back in history, but closer to Lombardy, in 1562 a rockslide off Monte Cremme dammed the river Brenna. On 29–30 May 1565, the dam collapsed and the resulting ‘Biasco flood wave’ killed 500 individuals as it swept the Brenna valley as far as Lago Maggiore. Ibid.

²⁹ Reported in Eisbacher and Clague, op. cit.

³⁰ [Anon], Discours deplorable d'un estrange accident survenu le septiesme Septembre, au Bourg de Plurs en la vallee de Valtoline, sujets des Grisons scis sur la riviere de Maira (Lyon, 1618), 7–8.

³¹ See the plate by Merian Matthaeus, published in Martin Zeiller, Topographia Helvetiae, Rhaetiae et Valesiae (Frankfurt, 1654), which depicts Plurs before and after the landslide.

³² Leibniz, Protogaea, 117. He also refers to it in a later letter to Louis Bourguet (May 1714), LBr 817 Bl. 66-71.

³³ Spon relates a similar incident occurring some years afterwards. He writes that on 21 November 1651, there occurred ‘a great overflowing of the Arve, which swept away almost all of the bridges, and made the Rhône rise up on the side of the lake, to the point that the mills of Geneva turned backwards’. Spon, Histoire de la Ville et de l'Estat de Geneve, II: 244.

³⁴ [Anon], Discours deplorable, 8.

³⁵ See Fausto Guzzetti, Colin P. Stark, Paola Salvati, ‘Evaluation of Flood and Landslide Risk to the Population of Italy’, Environmental Management, 36 (2007), 15–36; P. Salvati et al., op. cit.

³⁶ [Anon.], Newes from Spain:A True Relation of the Lamentable Accidents, caused by the Inundation and rising of Ebro, Lobregat, Cinca and Segre, Rivers of Spaine (London, 1618), page numbers not given. This is an English translation of a pamphlet originally written in Spanish by V. Rejaule, the King's Advocate, and published in Valencia, 1617.

³⁷ The history of hydrology is not well researched. The most comprehensive text is Asit K. Biswas, History of hydrology (Amsterdam, 1970). The discussion immediately below is informed by this book.

³⁸ ‘All rivers run to the sea; yet the sea is not fully unto the place whence the rivers come, thither they return again’. Ecclesiastes 1.7 (King James translation).

³⁹ Elements of both theories can be traced back to classical Greece. Aristotle, whose writings remained authoritative until the time of the European Renaissance, elaborated aspects of both. Similarly, Leonardo da Vinci (1452–1519) expounded both theories (on the same manuscript sheet!), though his writings remained unpublished. Precipitation measurements began to become common in the 18^th century, but it was the mid-19^th century before streamflow measurement became a routine activity.

⁴⁰ Georgius Agricola, De re metallica (Basil, 1556). English translation: De re metallica, trans. Herbert Clark Hoover and Lou Henry Hoover (New York, 1950). This book remained influential for more than a century, and Leibniz knew it well, citing it in various writings.

⁴¹ René Descartes, Discours de la méthode, incorporating an essay Les météores (1637), which contains some elements of a modern approach to evaporation and precipitation. However, he did not connect these phenomena with runoff, expounding instead the subterranean theory.

⁴² Athenasius Kircher, Mundus subterraneus (Amsterdam, 1664). This was the standard textbook of geology of the 17^th century. A fellow Jesuit, Gaspard Schott (1608–1666) allowed that rainfall might feed small streams.

⁴³ Johann Joachim Becher, Chymisches laboratorium (Frankfurt, 1680).

⁴⁴ Bernhardus Varenius, Geographia generalis (Amsterdam, 1650).

⁴⁵ Bernard Palissy, Discours admirables, de la nature des eaux et fontaines, tant naturelles qu'artificielles, des metaux, des sels & salines, des pierres, des terres, du feu et des emaux (Paris, 1580). English translation: The Admirable Discourses of Bernard Palissy, trans. Auréle La Rocque (Urbana, 1957).

⁴⁶ There are other indications that ordinary folk of the fields and hills shared elements of this more sophisticated knowledge. We find in pamphlets of the day testaments such as the following, which clearly demonstrates appreciation of a rainfall-runoff relation: ‘The sixt and last reason why the fens are often drowned, is because there is no Land Eayes to receive the surplussage of the waters which proceed from Raine and Snow falling upon the high Lands adjacent to the Fens, and to carry them into those Rivers or Draines which are next unto them.’ A Briefe Relation discovering plainely the true Causes why the great Levell of Fenns in the severall Counties of Norfolk, Suffolk, Cambridge, Huntington, Northampton, and Lincoln Shires; being three hundred and seven thousand acres of Low-Lands, have been drowned, and made unfruitfull for many yeares past (London, 1642), 6.

⁴⁷ Isaac Voss, Variarum observationum liber (London, 1685).

⁴⁸ Honoré Fabri, Physica (Lyon, 1670), vol. 3.

⁴⁹ Gilbert Burnet, Some Letters, Containing an Account of what Seemed Most Remarkable in Switzerland, Italy & etc. (Rotterdam, 1686), 14.

⁵⁰ De l'origine des fontaines: originally a privately circulated document, published anonymously in 1674, translation by A. LaRocque, Origin of fountains (New York, 1967).

⁵¹ Perrault relied on rather crude precipitation measurements and made first order estimates for the runoff by estimating channel dimensions and flow velocity.

⁵² Edmé Mariotte, Traité du mouvement des eaux et des autres corps fluides (Paris, 1686).

⁵³ The wisdom of God manifested in the works of creation (London, 1691).

⁵⁴ Edmond Halley, ‘An estimate of the quantity of vapour raised out of the sea by the warmth of the sun’, Philosophical Transactions 16 (1687), 366–70; ‘An account of the evaporation of water’, Philosophical Transactions 18 (1694), 183–90.

⁵⁵ It is interesting that all three of these investigators made (and got away with) essentially indefensible assumptions. In the case of Perrault and Mariotte, it was that rainfall at a point adequately indexes water input to a more or less extended region. Furthermore, their streamflow estimates were undoubtedly very poor. In Halley's case, the extension of very limited point measurements to a large part of Earth's surface is inadmissible. They got away with these assumptions because, in both cases, they were comparing one quantity (respectively, runoff or precipitation onto the land) with another, very much larger quantity (respectively rainfall and evaporation from the sea). In the first case, runoff is a small residual difference between rainfall and evaporation; in the second, rainfall onto the land comprises a small part of global evaporation, most of which reprecipitates onto the world ocean. So the undoubted gross biases in their ‘measurements’ disappeared into the magnitude of the unassessed additional term.

⁵⁶ Leibniz was certainly aware of Perrault's book (see Sämtliche Schriften und Briefe, III 2, 407), though there is no evidence that he ever read it.

⁵⁷ Their correspondence largely concerned topics in physics (colours, mechanics, etc.).

⁵⁸ He writes to Bernoulli in 1698: ‘That little book [Traité du movement des eaux] was never published, because the author was prevented by death; yet I do not doubt that it is circulating in the hands of some. If it could be obtained, I would gladly pay the price’. Leibniz to Johann Bernoulli (7/17 June 1698), in Sämtliche Schriften und Briefe, III 7, 795. This means Leibniz had not read Traité du movement des eaux at the time of writing the Protogaea.

⁵⁹ See Leibniz's unpublished notes from 1701 on Mariotte's Traité du movement des eaux, in the manuscript held in the Gottfried Wilhelm Leibniz Bibliothek, Hanover, shelf mark LBr 413, Bl. 69. Leibniz's notes relate to the section of Mariotte's book concerning the origin of winds (pp. 34–73 of the 1686 edition of the Traité). Among the topics that caught Leibniz's attention was Mariotte's explanation of the role of the winds in the November rains in central and southern France.

⁶⁰ Leibniz later recounted to one correspondent how he had witnessed experiments in the presence of Mariotte, and near the end of life—and almost thirty years after Mariotte's passing—he described Mariotte as a friend. For the former, see Leibniz to Simon Foucher (23 May 1687), in Sämtliche Schriften und Briefe, II 2, 203, and for the latter, see Leibniz to Varignon (28 June 1713), in Leibnizens mathematische Schriften, edited by C. I. Gerhardt (Halle, 1859), IV: 193.

⁶¹ There are references in Leibniz's writings to some of the papers Halley published in that journal; for example, he mentions ‘An account of the cause of the change of the variation of the magnetical needle, with an hypothesis of the structure of the internal parts of the earth’, Philosophical Transactions (19/29 October 1692), 563–78. See Leibniz's letter to Huygens (4/14 September 1694), Sämtliche Schriften und Briefe, III 6, 184.

⁶² See Sämtliche Schriften und Briefe I 22, 756.

⁶³ In his diary (Tagebuch) entry for 26 September/6 October 1697 Leibniz wrote ‘There should also be some translation done of Palissy's book’. G. W. Leibniz, Gesammelte Werke aus den Handschriften der Königlichen Bibliothek zu Hannover. Erste Folge, Vierter Band, edited by Georg Heinrich Pertz (Hanover, 1847), 218. Unfortuately it is not clear which of Palissy's books Leibniz had in mind; his access to a number of the royal libraries of Germany means that he had access to all of Palissy's works.

⁶⁴ Brocken, the highest mountain of the Hartz

⁶⁵ Leibniz, Protogaea, 19–21. It is worth noting that Leibniz also had his own first-hand experience to draw on. Much of his work in the Harz mines involved designing and overseeing wind-driven pumps to pump out the water which constantly seeped into the mines, hampering the extraction of silver. At the very least, we may surmise that his experience trying to raise water out of mines is likely to have made him particularly suspicious of the ‘subterranean plumbers’ and their idea of raising water to the mountain tops, if not actually affording him positive data and insights about the natural movement of water.

⁶⁶ Leibniz, Protogaea, 57.

⁶⁷ Biswas, op. cit.

⁶⁸ Transcribed from the manuscript held by the Gottfried Wilhelm Leibniz Bibliothek, Hanover, shelf mark LH VI, 1, Bl. 1–2.

⁶⁹ par | l'une et l'autre | deleted.

⁷⁰ ¶ Des grandes pluyes suffisent | deleted

⁷¹ une | campagne entiere, et les lits des rivieres | deleted.

⁷² endroit | ou l'on passé ordinairement | deleted.

⁷³ septembre | sont allees quelques fois à la hauteur | deleted.

⁷⁴ soupçonnay | qu'il y avoit un tremblement de terre sousmarin joint au vent terrible (α) et que meme ce vent surtout (β) de la terre et cela a esté confirmé par les relations des voyageurs. Mais il n'est | deleted.

⁷⁵ faut | examiner si les inondations ont commence plus bas ou plus haut | deleted.

⁷⁶ determiner | si il en faut attributer la cause de l'abondance | deleted.

⁷⁷ Benedicte Henriette, Duchess of Hanover (1652–1730).

⁷⁸ by | both | deleted.

⁷⁹ combined. | ¶ Substantial rains are sufficient | deleted.

⁸⁰ on | the whole countryside and the river channels | deleted.

⁸¹ September | sometimes went up to | deleted.

⁸² Leibniz is referring here to de la Hire's ‘Observation du barometre, du thermométre, & de la quantité d'eau de pluie & de neige fondue qui est tombée à Paris dans l'Observatoire Royal pendant l'année 1699’, Histoire de l'Academie Royale des Sciences (1700), 6–9, especially 6–7.

⁸³ For further details see Leibniz, Protogaea, 121.

⁸⁴ For further details see Leibniz, Protogaea, 123.

⁸⁵ See Cassiodorus, Variae 12.24.

⁸⁶ Marcus Aemilius Scaurus (c. 168-88BCE), Roman statesman. Leibniz is thinking of the following passage from Strabo's Geography V.1.11. ‘there is also a voyage thence by the Padus down to Ravenna which takes two days and nights. Now a considerable part of Cispadana too used to be covered by marshes (through which Hannibal, on his advance against Tyrrhenia, passed only with difficulty); but Scaurus drained the plains by running navigable canals from the Padus as far as Parma; for near Placentia the Padus is joined by the Trebia, as also before that by several other rivers, and is thus made excessively full. This Scaurus is the man who constructed the Aemilian Way which runs through Pisa and Luna as far as Sabata and thence through Derton’.

⁸⁷ Leibniz may here have in mind one or other of the events recounted in the Protogaea: ‘I will not speak of mountain collapses, like what happened in the canton of Bern, in the Alps of Villach, and in the Rhaetian Alps, where, as our fathers remember, the town of Plüos was smothered, and also in the territory of Firmano, where the so-called Mountain of the Caverns collapsed in 1670’. Leibniz, Protogaea, 117.

⁸⁸ Leibniz made the same reference in the Protogaea: ‘The history of Geneva recounts how winds stopped the flow of the Rhône River, piling its waters into a heap and making it possible to walk across the dry riverbed’. Protogaea, 57. The reference is to what Jacob Spon, the author of the history of Geneva, called ‘an odd thing which occurred in Geneva on Sunday the 19th of January 1645 between seven and ten o’ clock in the morning’. Spon explains: ‘After thunderstorms had raged all night, there arose such a strong wind that in no time at all it drove back the Rhône and the Lake [Geneva] to such an extent that for two hours various people went to the chains on foot and stayed dry, and others crossed from Monnoye to the Island’. Jacob Spon (note 18) : II, 239.

⁸⁹ Leibniz refers to a Mr Worsley in the New Essays (1703–5), describing him as an ‘observant traveller’; see Sämtliche Schriften und Briefe, VI 6, 248. The editors from the Berlin Academy have been unable to identify him, however, and conjecture that he may be the Mr Wichley briefly discussed by Leibniz and Electress Sophie, in an exchange of letters in 1703. See Sämtliche Schriften und Briefe, I 22, 97 and 102.

⁹⁰ suspected | that there was an underwater earthquake together with a terrible wind (α) and that this wind especially (β) over the land, and this has been confirmed by travellers’ accounts. | deleted.

⁹¹ should | investigate whether the inundations begun lower or higher | deleted.

⁹² determine | if the cause of the abundance should be attributed to | deleted.