The aim of this paper is to investigate the notion of need, in this case an entire city's global need for water. This was a notion invented by Paris technicians between 1760 and 1804 in the context of several water supply projects, notably two river diversion schemes, those of the Yvette and the Ourcq, where the concept was much discussed. Different ways of considering the question of need – such as water resources, consumption and use, whether present or future – were strongly related to engineers' or scientists' conceptions of their own work. State engineers claimed they could make objective estimates of future needs with no reference to either value judgements or political intentions, a position which made it possible to keep strong control over the decision in the name of the state. In contrast, a practically trained engineer working outside the state corps claimed that in the case of expertise about the future, estimates would depend strongly on political intentions, norms and ideals, so the government should first give an outline of its intended actions. The paper studies the differences between these two approaches to the concept of need, especially how they articulated knowledge about what is and knowledge about what ought to be, present and future. The paper ends by linking these differences to conceptions of what was supposed to be technical or political in such projects and of what role engineers intended to play in the decision-making process.

In 1823 the astronomer Friedrich Wilhelm Bessel gave notice of an observational error which is now known as the personal equation. Bessel, however, never used this phrase to characterize the finding that when noting the time of a certain event observers show a considerable ‘involuntary constant difference’. From this starting point the paper develops two arguments. First, these involuntary differences subverted the concept of the ‘observing observer’. What had previously been defined as a reference point of trust and precision turned into a source of an error that resisted any wilful intervention. Second, and contrary to later suggestions, Bessel's findings did not initially lead to discussions and measures of permanent control. In everyday astronomical work the influence of such differences could be avoided by comparatively simple means. Taking this into account offers a new perspective both on the history of the personal equation and on the significance of Bessel's findings. Whereas the former has to be read as the history of a rather particular reaction to the phenomenon of constant differences, the latter is connected with a rather fundamental transition in the epistemology of the observer.

This paper examines the debate engendered in ethnological and anthropological circles by Darwin's Origin of Species and its effects. The debate was more about the nature of human diversity than about transmutation. By 1859 many polygenists thought monogenism had been clearly shown to be an antiquated and essentially religious concept. Yet the doctrine of natural selection gave rise to a ‘new monogenism’. Proponents of polygenism such as James Hunt claimed natural selection had finally excluded monogenism, but Thomas Huxley, the most prominent exponent of the new monogenism, claimed it amalgamated the ‘best’ of both polygenism and monogenism. What it did provide was an explanation for the irreversible inequality of races, while it maintained that all humans were of one species. This bolstered belief in the innate superiority of the Caucasians over other peoples. The effect was finally to sever British ethnology from its evangelical monogenist roots. More subtly and surprisingly, it provided support in Church circles for a move away from the ideal of the ‘Native Church’.

While important research on the history of scientific commemorations has been published in recent years, relatively little attention has been paid to the commemoration of invention and inventors. A comparison of the centenaries of James Watt's death in 1919 and of Michael Faraday's discovery of electromagnetic induction in 1931 reveals how the image of the inventor was being refashioned in the early twentieth century. Although shortly after his death Watt had been acclaimed by the Royal Society as a great ‘natural philosopher’, a century later his reputation had been appropriated by the engineering professions and trades. As the title of Dickinson's 1935 biography described him, he was seen primarily as a ‘craftsman and engineer’, not a scientist. With poor publicity, which failed in particular to make any connection between steam power and electricity, the 1919 centenary excited little interest outside engineering circles. Meanwhile, professional scientists, who were seeking financial recognition for the importance of their research in ‘pure’ science, had found a new icon in Michael Faraday. They seized the occasion of the 1931 centenary to reinforce the link between Faraday's scientific research and the wonders of modern electrical technology and thereby to elevate the role of ‘blue-sky’ research over its ‘mere’ application.

The Cambridge school of animal morphology dominated British zoology in the late nineteenth century. Historians have argued that they were very successful until the death of their leader F. M. Balfour in 1882, when the school all but died with him. This paper argues that their initial success came about because their work fitted well with the university in the 1870s and 1880s. They attempted to trace evolutionary trees by studying individual development. To do this they needed access to species they considered primitive. Balfour made use of his social networks to aid the school and to collect the specimens they needed for their work. The school has been portrayed as failing in the 1890s when students rejected dry laboratory-bound studies. However, a new generation of researchers who followed Balfour had to travel extensively if they were to obtain the organisms they needed. International travel was popular amongst zoologists and the Cambridge school developed their own extensive networks. A new breed of adventurer–zoologists arose, but because of the school's tenuous position within the university they were unable to equal Balfour's success.