The sixth weighty tome of John Tyndall's voluminous correspondence follows the pattern set for the previous volumes by the general editors of the series, James Elwick, Roland Jackson, Bernard Lightman and Michael S. Reidy, namely a helpful introduction to the 302 letters printed in the present volume; timelines of Tyndall's life overall (1822–93) and, in greater detail, between November 1856 and March 1859 when the letters were written or received; and a thirty-one-page register of the names and biographies of people who are mentioned three or more times in the letters included in this volume. A comprehensive index of names and topics concludes the volume, and all the letters are cross-referenced within and between the volumes published to date.

The editing (shared between four scholars from Canada, the USA, England and Ireland for greater speed of production) is meticulous and helpful in dating undated letters and identifying people and places, publications, literary references and any scientific concepts or experiments discussed in the letters. The editors occasionally nod, as when Mrs Louisa Tyndall's transcription of letter 1401 by Mrs Juliet Pollock is printed as referring to a ‘Mrs Crosser's Memorial of her Husband’ instead of to Cornelia Crosse's biography of her electrician husband; and no man of science, let alone Edwin Lankester, was president of the British Association for twenty-five years (letter 1488), whatever Wikipedia may say. Because the Royal Institution has been celebrating the bicentennial of Tyndall's birth this year (2020) in COVID-muted form, it is interesting to find further confirmation in one of Tyndall's own letters (item 1366) that he was probably born in 1822, not 1820.

What of the subject matter? By November 1856 Tyndall had been professor of natural philosophy at the Royal Institution for three years and a fellow of the Royal Society for four years. His scientific interest had moved from diamagnetism to the problem of glaciation as a result of a trip to Switzerland in the summer of 1856. He returned to the Swiss Alps in the summers of 1857 and 1858 in order to gather further evidence for his theory of the cause of glaciation which opposed that of his Scottish competitor, James David Forbes. The editorial introduction (and a helpful map of places in the Alps) provides both an excellent short account of Tyndall's work on the glaciers and of his daring climbing exploits (he climbed Mont Blanc in 1857), and context for the many letters to Faraday and other friends describing his exploits. The volume ends with Tyndall negotiating terms with publishers for his first popular book, The Glaciers of the Alps, which would not appear in print until 1860. The other topics highlighted by the editors’ Introduction provide context for Tyndall's professional activities as a lecturer at the Royal Institution in Albemarle Street and the London Institution in the City of London's Finsbury Square, his activities as an examiner for the Royal Military Academy at Woolwich, and his continuing friendship with French and German scientists whom he had met and worked with as a mature student between 1848 and 1851.

The third, and in many ways the most gripping, of the volume's themes is the editorial discussion of Tyndall's private life. To his most intimate friend, Thomas Archer Hirst, who devastatingly loses his Irish wife to tuberculosis during the course of the present correspondence, Tyndall confesses that he is in love with May Drummond, the eldest of three daughters of the rich widow and literary hostess Maria Drummond. In the eyes of the modern reader of the letters and of Tyndall's unpublished private journals, the affair was farcical. It is obvious, on the one hand, that widow Drummond (who was ten to twelve years older than Tyndall) had her own designs on him as his intellectual equal, and on the other, that Tyndall could not make up his mind which of two daughters he preferred. Both May and Emily Drummond were flirts, testing their late adolescent sexuality with the obliging father figure of Tyndall. Fortunately for science and Victorian culture, Tyndall came to his senses when he confessed to Hirst that marriage into the Drummond family would mean a life of opulent idleness and an endless round of soirées and no time for research, writing or controversy. He was not to marry Louisa Hamilton until 1876, when he was in his fifties and she in her early thirties.

As Geoffrey Cantor and I were struck when editing volume 5, Tyndall seems to have been casually indifferent to the fate of his mother and sister in Ireland. There are only two letters to his mother and none to his sister. Close friends from his previous life in Ireland and as a railway surveyor in Yorkshire have also disappeared from the record. The exceptions are his close friends from his time as a teacher at Queenwood College – Edward Frankland, Heinrich Debus and, especially, his pupil and confidant, Thomas Archer Hirst. His American cousin, Hector Tyndall, is represented by only one outstandingly interesting Whitmanesque letter (item 1311). There are also many delightful vignettes waiting to be mined by historians of Victorian science: Debus's lifelong failure to master the English language, Herbert Spencer's incomprehensible lucubration on ‘the doctrine of ultimate equilibrium’ (item 1593), and Gustav Magnus revealing himself to have been a bit of a sourpuss know-all as well as an outstanding experimentalist, to name but a few. Students of Victorian science and culture will value libraries that purchase this treasure house of correspondence.