In summer 2018, I was the sole Undergraduate Research Assistant for a project entitled ‘The Fever Tree’. This initiative, jointly run by Dr Marc Etherington (Physics) and Dr David Lowther (History) at Durham University and sponsored by the Hatfield Trust, aimed to understand the changing interest in quinine and divergent routes of study throughout the nineteenth and twentieth centuries.

My main responsibility during this internship was to transcribe nineteenth-century scientific correspondence. The aim was to analyse how the study of quinine – a compound derived from the bark of the cinchona tree and the key component of tonic water – changed over time, ultimately resulting in quinine’s reputation as a valuable antimalarial and fluorescence standard.


Cinchona of St Lucia: plate 19 from ‘An account of a new species of the Bark-tree, found in the Island of St Lucia’ by George Davidson, Philosophical Transactions of the Royal Society, vol.74 part 2 (1784), pp.452-456.


I arrived at the Royal Society Library carrying a list of documents to find and photograph for further study. There was a wonderfully studious atmosphere in the reading room – mostly silent, with the occasional frustrated groan when somebody couldn’t decipher a particular word! Others would then chip in to help figure out what was written, testament to the collegial atmosphere. I would like to thank Louisiane Ferlier, who enabled my visit and has been incredibly supportive of the project.

My transcriptions mainly focused on the writings of English polymath Sir John Herschel (1792-1871), Irish physicist Sir George Stokes (1819-1903), and Scottish science writer Mary Somerville (1780-1872), and the emergent network of scientists pieced together via correspondence. This tracing of networks and identifying incidental figures is in vogue, as I learnt at the European Society for the History of Science (ESHS) biennial conference. This addressed the recently-released website Epsilon (‘A collaborative digital framework for nineteenth-century letters of science’), which aims to gather together the correspondence of bigger names such as Darwin, while enabling archivists to discover those in relative obscurity.

In 1845, Sir John Herschel was the first to discover and describe the fluorescent properties of quinine. In his experiments, Herschel transmitted a beam of sunlight through a solution of sulphate of quinine and found that a vivid blue colour appeared at the surface of the transparent liquid, but only in the layer of liquid next to the surface by which the light entered. Herschel named this phenomenon ‘epipolic dispersion’.


Portrait of George Gabriel Stokes by Hubert von Herkomer, 1891 © The Royal Society


This work served as the inspiration for Sir George Stokes, who described the concept of fluorescence in great detail as part of his 1852 treatise ‘On the change of refrangibility of light’, featuring studies on quinine sulphate and published in the Philosophical Transactions of the Royal Society. Stokes used a prism to disperse the solar spectrum and illuminate a solution of quinine, noticing that there was no effect until the solution was placed in the ultraviolet region, leading to the discovery of the eponymous Stokes shift.


Sculpture bust of Mary Somerville by Francis Legatt Chantrey, 1840 © The Royal Society


Mary Somerville overcame many of the barriers to women in the academic sphere of the nineteenth century and was a close family friend of Herschel’s; the two communicated frequently. There is, though, a gap in correspondence between 1831 and 1843, presumably because Somerville relocated to Italy. This is unfortunate, given that Herschel published his quinine findings in 1845 – correspondence might have given more insight. However, Somerville’s work On the Molecular and Microscopic Sciences does contain detailed discussion surrounding Herschel’s findings. Herschel also urged Mary to observe astronomical phenomena, but she was unable to do so as the Jesuit-founded Collegio Romano refused to admit women to its observatory. Incidentally, the Jesuits were instrumental in bringing cinchona bark to Europe from South America.

It appears that Herschel was content to allow others to take over following his initial discovery. It is this fact that renders tracing studies on quinine so challenging, as the network became incredibly broad. Stokes outlived Herschel by a few decades and so can be considered a ‘bridge’ between the nineteenth and twentieth centuries. However, both Herschel and Stokes moved away from the study of quinine fluorescence in their later years. The major question here, which remains largely unanswered, is: who ‘picked up’ the study of quinine? The path taken by quinine – in the lead up to its being used to alleviate the suffering of soldiers in early twentieth-century combat – remains decidedly unclear.

I delivered a well-attended talk at Hatfield College on the main findings of my project, featuring both a Q&A section and a live demonstration of quinine fluorescence… as well as complementary gin and tonic! I am told that my 150+ transcriptions may well be uploaded as part of a trial period of the Epsilon project. I have benefitted hugely from this internship in terms of my own personal and academic development, so it would be fantastic to contribute directly to future projects.

In 1852, Stokes wrote to Herschel: ‘your ‘epipolic’ dispersion has given me the clue to a most extensive field of research…’. It likewise gave me an insight into my own aspirations: as of September 2019, I am studying for an MSc in Medical Anthropology.