Natural Histories and Newton’s Theory of the Tides
Kirsten Walsh writes…
Lately, I’ve been thinking about Newton’s work on the tides. In the Principia Book 3, Newton identified the physical cause of the tides as a combination of forces: the Moon and Sun exert gravitational pulls on the waters of the ocean which, together, cause the sea levels to rise and fall in regular patterns. This theory of the tides has been described as one of the major achievements of Newtonian natural philosophy. Most commentators have focussed on the fact that Newton extended his theory of universal gravitation to offer a physical cause for the tides—effectively reducing the problem of tides to a mathematical problem, the solution of which, in turn, provided ways to establish various physical features of the Moon, and set the study of tides on a new path. But in this post, I want to focus on the considerable amount of empirical evidence concerning tidal phenomena that underwrites this work.
Let’s begin with the fact that, while Newton’s empirical evidence of tidal patterns came from areas such as the eastern section of the Atlantic Ocean, the South Atlantic Sea, and the Chilean and Peruvian shores of the Pacific Ocean, Newton never left England. So where did these observational records come from?
Newton’s data was the result of a collective effort on a massive scale, largely coordinated by the Royal Society. For example, one of the earliest issues of the Philosophical Transactions published ‘Directions for sea-men bound for far voyages, drawn up by Master Rook, late geometry professour of Gresham Colledge’ (1665: 140-143). Mariners were instructed “to keep an exact Diary [of their observations], delivering at their return a fair Copy thereof to the Lord High Admiral of England, his Royal Highness the Duke of York, and another to Trinity-house to be perused by the R. Society”. With respect to the tides, they were asked:
“To remark carefully the Ebbings and Flowings of the Sea, in as many places as they can, together with all the Accidents, Ordinary and Extraordinary, of the Tides; as, their precise time of Ebbing and Flowing in Rivers, at Promontories or Capes; which way their Current runs, what Perpendicular distance there is between the highest Tide and lowest Ebb, during the Spring-Tides and Neap-Tides; what day of the Moons age, and what times of the year, the highest and lowest Tides fall out: And all other considerable Accidents, they can observe in the Tides, cheifly neer Ports, and about Ilands, as in St. Helena’s Iland, and the three Rivers there, at the Bermodas &c.”
This is just one of many such articles published in the early Philosophical Transactions that articulated lists of queries concerning sea travel, on which mariners, sailors and merchants were asked to report. In its first 20 years, the journal published scores of lists of queries relating to the tides, and many more reports responding to such queries. This was Baconian experimental philosophy at its best. The Royal Society used its influence and wide-ranging networks to construct a Baconian natural history of tides: using the method of queries, they gathered observational data on tides from all corners of the globe which was then collated and ordered into tables.
Newton’s engagement with these observational records is revelatory of his attitudes and practices relating to Baconian experimental philosophy. Firstly, especially in his later years, Newton was regarded as openly hostile towards natural histories. However, here we see Newton explicitly and approvingly engaging with natural histories. For example, in his discussion of proposition 24, he drew on observations by Samuel Colepresse and Samuel Sturmy, published in the Philosophical Transactions in 1668, explicitly offered in response to queries put forward to John Wallis and Robert Boyle in 1665:
“Thus it has been found by experience that in winter, morning tides exceed evening tides and that in summer, evening tides exceed morning tides, at Plymouth by a height of about one foot, and at Bristol by a height of fifteen inches, according to the observations of Colepress and Sturmy” (Newton, 1999: 838).
I have argued previously that Newton was more receptive to natural histories than is usually thought. The case of the tides offers additional support for my argument. Newton’s notes and correspondence show that, from as early as 1665, he was heavily engaged in the project of generating a natural history of the tides, although he never contributed data. And eventually, he was able to use these empirical records to theorise about the cause of the tides. This suggests that Newton didn’t object to using natural histories as the basis for theorising. Rather, he objected to treating natural histories as the end goal of the investigation.
Secondly, I have previously discussed the fact that Newton seldomly reported ‘raw data’. The evidence he provided for Phenomenon 1, for example, included calculated average distances, checked against the distances predicted by the theory. Newton’s empirical evidence on the tides, as reported in the Principia, was similarly manipulated and adjusted with reference to his theory. Commentators have largely either condemned or ignored this ‘fudge factor’, but such adjustments are ubiquitous in Newton’s work, suggesting that they were a key aspect of his practice. Newton recognised that ‘raw data’ had limited use: to be useful, data needed to be analysed and interpreted. In short, it needed to be turned into evidence. The Baconians appear to have recognised this: queries guide the collection of data, which is then ordered into tables in order to reveal patterns in the data. As this case makes clear, however, Newton’s theory-mediated manipulation of the data went beyond basic ordering, drawing on causal assumptions to reveal phenomena from the data.
Thirdly, this case emphasises Newton’s science as embedded in rich social, cultural and economic networks. The construction of this natural history of tides was an organised group effort. That Newton had access to data collected from all over the world was the result of hard work from natural philosophers, merchants, mariners and priests who participated in the accumulation, ordering and dissemination of this data. Further, the capacities of that data to be collected itself followed the increasingly global trade networks reaching to and from Europe. Newton’s work on the tides was the very opposite of a solitary effort.
On this blog, we have noted in passing, but not explored in depth, the crucial roles played by travellers’ reports and information networks in Baconian experimental philosophy. Newton’s study of the tides is revelatory of the attitudes and practices of early modern experimental philosophers with respect to such networks. I shall discuss these in my next post.