This paper examines the usefulness of the category ‘interest’ in the history of technology through a case study of the failed attempt to introduce atmospheric railway traction in Britain in the 1840s. It argues for a reflective deployment of the term in question, sensitive to contemporary usages. A schematic typology of railway ‘interests’ shows just how various these were. Financial interests, for example, were not the same as professional ones; or an investor might feel the pull of contrary interests, depending on whether she was checking her dividends or taking a train. The history of atmospheric traction demonstrates the interlocking of railway ‘interests’, and their utility in explaining the success or failure of railway technologies. As might be expected, determinism, whether technological or ‘social’, does not answer the case. ‘Interest’ relations are contingent, and so must be understood the failure of the atmospheric railway.

Fleeming Jenkin's swamping argument (1867) is re-examined in relation to subsequent criticisms of its assumptions. Jenkin's original argument purported to show that, under blending inheritance, natural selection could not operate on ‘sports’ or ‘single variations’. A serious flaw in Jenkin's model was exposed in a forgotten paper in 1871. Darwin accepted Jenkin's ‘flawed’ conclusion, though he did not fully understand the argument. Both Jenkin and Darwin regarded the swamping argument as a barrier to evolution within a single lineage. A completely different interpretation of the phrase ‘swamping argument’, first put forward by Romanes in 1886, identified it with the problem of the role of free intercrossing in preventing speciation. The latter problem also underlies current debate about the possibility of sympatric speciation and is as serious under particulate as under blending inheritance. Jenkin's argument depended on the assumption of blending inheritance; when modified to remove the ‘flaw’ in his model, it ceased to present a barrier to the operation of natural selection within a lineage, provided that the mutation rate was high enough to maintain adequate genetic variability under blending.

In this paper I address C. A. Coulson's teaching activities, writing textbooks and delivering popular science lectures, as well as his popular lectures on religion and the ‘scientific’ sermons delivered in his capacity as a lay preacher of the Methodist Church. I will pay particular attention to his thoughts on science. His commitment to forging a way to reconcile science and religion was built upon a reflection on the aims and methods of science within the broader framework of science's role in post-Second World War society. By noting that Coulson valued chemistry, mathematics and science in general, as a kind of religious activity, I argue that he wrote masterful textbooks and delivered popular science lectures as lay sermons. These were activities which Coulson pursued energetically to build a community of science adepts and proselytes. And winning young, and indeed not so young, people to science meant teaching them one of the languages that could be used to reach God. In the same way, I extend my argument to his popular lectures on religion and his ‘scientific’ sermons and claim that they should be viewed as popular science lectures addressed to an audience that was often ignorant, or even suspicious, of science.