John Stevens Henslow

6 February 1796 – 16 May 1861
John Stevens Henslow by Thomas Herbert Maguire, 1851.

Image: John Stevens Henslow by Thomas Herbert Maguire, 1851.

John Stevens Henslow was a naturalist, a Cambridge academic, most remembered as a friend and mentor of Charles Darwin, inspiring him with a passion for natural history, proposing him to sail on the HMS Beagle as the naturalist on its five-year voyage, and promoting Darwin’s work as he developed his theory of evolution. Within Cambridge, he was the driving force behind setting up the Botanic Garden in its current location, and was also notable as one of the founders (together with Adam Sedgwick and Edward Clarke) of the Cambridge Philosophical Society in 1819.

Henslow and Cambridge University
Henslow came as an undergraduate student to St John’s College in 1814. He had been passionately interested in natural history as a child but at that time the Cambridge degree was mainly devoted to mathematics; there were no degrees specialising in the sciences and attendance at any lectures in these subjects was entirely voluntary.  A Cambridge degree was seen mainly as a ticket to a career in the Church, and most College Fellows and University Professors were ordained. Henslow was ranked 16th in his Tripos examinations in 1818, which was not good enough for him to immediately move to a Fellowship in the University. However, he chose to remain in Cambridge, furthering his studies in natural history, collecting specimens in the field which he meticulously sorted and analysed. He very soon became involved in teaching and was able to start passing on his enthusiasm and wide knowledge of different aspects of natural history to members of the University. He was an inspirational teacher, using experimental observations and field trips to encourage students to make observations on their own. 

Despite holding only a Bachelor’s degree he became Professor of Mineralogy in 1823, immediately making his mark as an excellent and inspirational lecturer. Botany was however his main interest, and in 1827 he was successful in being elected as Professor of Botany, following the death of Thomas Martyn who had held the Chair for 60 years; he resigned his other Chair soon after. Botany was at a low ebb in Cambridge: no lectures had been given for 30 years. Henslow soon had 60-80 students attending his lectures, including some ladies (who were at that time permitted to attend University teaching only by special arrangement). 

Botanic Garden
The Botanic Garden was a small plot used for growing medicinal plants in the middle of Cambridge in what is now the New Museums Site.  Henslow persuaded the University to purchase 40 acres of farmland to enable the establishment of Cambridge University Botanic Garden on its present site where all kinds of plants including trees could be grown for scientific study. The garden opened in 1846, providing the foundation for serious experimental botany which endures today as part of Henslow’s legacy. 

It was largely due to Henslow that the Natural Sciences Tripos was introduced in 1851, after many years of battling against the University authorities. Initially qualifying for the BA only in conjunction with another Tripos, it was another decade before the Natural Sciences Tripos stood alone. Henslow examined the first candidates in botany only weeks before his death.

Darwin and Henslow
As a student in Cambridge in 1828 Charles Darwin was studying for his bachelor’s degree, following the required courses in mathematics, theology and classics diligently enough to pass the examination but without enthusiasm. Like Henslow, natural history had been an over-riding interest for him from an early age, and at Cambridge Darwin devoted as much time as he could to collecting and studying insects and plants, on his own. Following advice from his brother Erasmus (who had preceded him as an undergraduate), Darwin joined Henslow’s botany course in Cambridge and became a regular attender on his botanical and geological field excursions as well as the weekly informal gatherings at his own home. A great friendship grew up between the two, and in his final undergraduate years Darwin became known as ‘the man who walks with Henslow’, frequently accompanying him in his natural history forays into the Cambridge countryside. 

In 1831 Henslow was invited to take the post of naturalist on the HMS Beagle which was due to undertake a two-year geographical and scientific survey of South America. His wife was unwilling to let him go, and Henslow instead recommended Charles Darwin, whose theory of natural selection developed out of this transformational experience. As he started gathering specimens and observing the geology and natural history of South America, it was natural that Darwin should turn to Henslow for guidance and discussion. Henslow took charge of the specimens that Darwin sent home during the voyage and the two corresponded regularly, discussing his findings and puzzling over their meaning. Henslow regarded his observations as sufficiently important that he read extracts from Darwin’s letters at a meeting of the Cambridge Philosophical Society in 1835, and followed this with a publication. Henslow continued to present and publish Darwin’s work through this route in the following years.

In his autobiography, Darwin states that the relationship with Henslow was ‘a circumstance which influenced my whole career more than any other’.

Founding of the Cambridge Philosophical Society
The idea of founding a society to promote research was conceived on a geological expedition to the Isle of Wight in the spring of 1819. Henslow, a fresh graduate, had accompanied Adam Sedgwick, the newly-appointed Woodwardian Professor of Geology, and they worked together to gather geological specimens and fossil shells, developing the techniques of field geology and trying to understand how the rocks had evolved. Geology was a new science that was evolving rapidly, but even by contemporary standards Sedgwick knew very little about it and was eager to learn everything he could. The research that Sedgwick and Henslow were doing was exciting and clearly of significance, but they realised that there was no forum in Cambridge for presenting their work. There was little scientific research in Cambridge, or indeed in the rest of England, and such activity as there was took place in private scientific societies. Rather than trying to introduce change into the University, they  conceived the idea of founding their own society, based in Cambridge and drawing on its talents, but able to act independently. Over the summer they prepared the ground by writing to friends and colleagues in Cambridge end elsewhere outlining their ideas. In the autumn they set to work, enlisting the help of Edward Daniel Clarke, Professor of Mineralogy, a talented and enthusiastic teacher who knew his way around the University and had a track record of making things happen.

In a remarkably short time, the Cambridge Philosophical Society was founded: for the purpose of promoting Scientific Enquiries and of facilitating the communication of facts connected with the advancement of Philosophy. The term science was not in currency, and the umbrella term of Natural Philosophy was used to describe experimental subjects.

The constitution was agreed on 19 November 1819 by the nine members of a committee drawn from different disciplines across the University including geology, mineralogy, anatomy, chemistry, astronomy and mathematics. The first papers were presented at a meeting in February 1920. The pattern of fortnightly meetings was established, and endures to this day. 

Publication of its own journal followed in 1821, Transactions of the Cambridge Philosophical Society, now divided into Mathematical Proceedings and Biological Reviews. A museum was created, the collections now dispersed elsewhere, and a library founded. This became the Scientific Periodicals Library, the biggest collection of scientific books and journals in Cambridge, and was assimilated into the University Library in the 1970s.

The Cambridge Philosophical Society was central to revitalising interest in research and teaching of science and mathematics in Cambridge at this time. From there its influence quickly spread to other parts of England, and abroad. 

Henslow at Hitcham
As was common in Cambridge, Henslow was ordained in 1824, soon after graduating, and gained some income by acting as the curate of Little St Mary’s Church. In 1833 he was appointed vicar of Cholsey-cum-Moulsford in Oxfordshire, but continued to live and work in Cambridge during University terms, appointing a curate to take on his duties in the parish. In 1837 however he was appointed to a living at Hitcham in Suffolk, 45 miles from Cambridge, a post that was well-paid and came with a vicarage. He moved there with his family in 1839 and  devoted increasing amounts of time and energy to improving the lives and wellbeing of his parishioners. He was very aware of the importance of education, and used his experience and teaching skills to provide resources in the village. He raised funds to found a village school for educating the children of the poor, and taught botany there himself as a core element of the curriculum. The poverty of this rural community was a great concern to him, and he worked tirelessly to improve the understanding and practice of agriculture through adult education at the Hitcham Labourers’ and Mechanics’ Society. In the course of this he noted that coprolites found locally could have value as fertiliser, leading to the establishment of the phosphate industry in Suffolk and Cambridgeshire. Through all this time, until his death in 1861, he continued to hold his Chair at Cambridge, teaching and examining and taking part in University activities, but his heart was elsewhere and his influence in Cambridge declined.

He died at Hitcham in 1861 aged 65 and is buried in the churchyard there; his portrait hangs in the church. Following his death, Charles Darwin wrote of him: “I believe a better man never walked this earth”.


The Spirit of Enquiry, Susannah Gibson. Oxford University Press, (2019)
The correspondence of Charles Darwin, Volume 1 1821-1836. Cambridge University Press (1985)
Darwin and Henslow, The Growth of an Idea. Letters 1831-1860, edited by Nora Barlow. University of California Press (1967)

Virtual tour of an exhibition about Henslow

History of Cambridge Botanic Garden

Article by Kim Smith in Bury and West Suffolk Magazines

Henslow as Rector of Hitcham, by David Turner (2017)

Wiki article

Society Timeline

  1. 1819

    Cambridge Philosophical Society Founded

  2. 1846

    New Botanic Garden opens

  3. 1848

    New Fitzwilliam Museum building opens

  4. 1851

    Natural Sciences Tripos starts

  5. 1874

    Cavendish laboratory opens

  6. 1884

    Balfour laboratory for women opens

  7. 1914

    Women first eligible as honorary fellows of CPS

    Marie Curie
    Marie Curie
  8. 1929

    Women eligible to be full fellows of CPS

  9. 1948

    Women first awarded degrees

  10. 1967

    Philosophical Library becomes Scientific Periodicals Library

  11. 2010

    Henslow Fellowship scheme launched

  12. 2019

    Society’s Bicentenary

    Blue Plaque, Saints Passage, Cambridge
    Blue Plaque, Saints Passage, Cambridge


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