Until fairly recently a common way of doing history of science was to pick up an important strand of contemporary scientific thought and to trace its origin back to the philosophical tangle of the scientific revolution. This approach conveniently by-passed the breakdowns of once useful and pervasive theories, and neglected the long intellectual journeys along devious routes. History of science read like a success story; the pioneers who failed were neither dismissed nor excused; they were simply ignored. The historian knew what he was hunting for and he was careful to limit his search to areas where his quarry was sure to be found. This method, which has been dubbed the precursor-view, stands in contrast—albeit, not in opposition—to the contextual method, which aims at a better understanding of the actual thought-processes of the early scientists. On this second view, history of science must not only account for present theories in the light of past developments, it must also assess old theories in terms of the scientist's conceptual framework, and judge them against the background of the world picture of his age. This may lead the historian down the blind alleys of the past, chasing spurious attempts at explaining the nature of physical reality, but it can clear the ground for a less anachronistic interpretation of the emergence of modern science and the actual process of discovery. History of science acts as a winnowing fork, but we cannot suppose that the discoverer himself always separated the wheat from the chaff, and we must be ever wary of equating the dream with the task.

“Tobias Mayer is universally considered as one of the greatest astronomers not only of the eighteenth century, but of all times and of all countries.” This is how the French astronomer, Jean Delambre, in his posthumously published Histoire de l'astronomie au XVIIIième siècle (Paris, 1827), introduces his readers to the Göttingen professor, whom Leonhard Euler had already recognized in 1760 as “undoubtedly the greatest astronomer in Europe”. Delambre's placing of Mayer in a historical perspective assumes special significance on account of the fact that he had previously written three volumes on ancient and medieval astronomy.

As a historical figure, Lamarck proves a rather difficult subject. His writings give us few explicit leads to his intellectual debts; nor do they present his theories as the outcome of any sustained course of observations or experimental research; and, what is equally frustrating, it is hard to see how his personal development as a scientific theorist was affected by the dramatic political and social upheavals of the period, in which he took an active and lively interest. And so, with his importance for later writers much clearer than his relationship to those of his own and earlier ages, historians have repeatedly interpreted his works as prophetic of doctrines developed more fully by subsequent generations. No less surprisingly, this facile tactic has provoked a reaction; we have been offered Lamarck as a Stoic, a romantic, harking back to Heraclitus.

Heat is the fundamental mechanism in the theory of the earth proposed by James Hutton in 1785. According to Hutton, heat is responsible for the liquefaction of loose debris collected on the ocean floor. Consolidation follows and the newly formed land is raised above the sea by the agency of heat. The expansive nature of heat that causes this elevation of land also accounts for the creation of veins and dykes through the injection of fluid matter into openings in the earth. The activity of heat is intermittent; there are times when it is active, but at other times it is dormant. In another paper I argued that Hutton's concept of this geological heat was an application of his theory of matter in which heat is an immaterial, universally operating force acting in opposition to forces of attraction. This concept of heat was quite different from the popular late eighteenth-century belief that heat was a material substance called caloric. The critics of Hutton repeatedly tried to interpret his heat as if it were caloric. Failing in this they found Hutton a confusion of idle speculation on heat and without theoretical basis. Further, since fire was a major source of caloric and since the already established geological tradition of Vulcanism called for fires within the earth, it was natural that these critics thought of Hutton's theory as being necessarily based on the presence of internal fires and questioned how such fires could exist, disregarding the fact that Hutton rarely mentioned fires and even disclaimed the necessity of fires in the production of heat. The criticisms concerning heat fall into several major groups of which the source of heat in only one. The others include the formation of the whinstone of Scotland and the crystallization of rock in general, the expansive role of heat, the intermittent activity of heat, and the temperature of the earth. Of these the formation of particular kinds of rocks was submitted to experimenal test by Sir James Hall, whose investigations were especially concerned with the effects of the rate of cooling on crystallization and the effects of pressure on the formation of rock. Much of the discussion of Hall's work centred on the experiments, and the theoretical problem about the nature of heat was obscured as a result. It is in the commentary on the other problems noted above that the true situation becomes clear. For this reason a study of these problems is more revealing and constitutes the following.

The most reliable source for a reconstruction of Galileo's progress toward a science of motion is the series of undated fragmentary notes on that subject preserved in Codex A of the Galilean manuscripts at Florence. A gathering of such fragments was published by Favaro in the National Edition of Galileo's works, following the Discorsi. The more sophisticated fragments are clearly associated with the composition of that work, and show a definite and consistent understanding of acceleration. Eliminating those, it will be found that the earlier notes fall into recognizable groups. First, there are some that refer to “moment of gravity”, or to the impetus of a body along a line of descent, and are associated with the discussion of inclined planes in De motu. Second, some refer to descent along arcs and chords of circles, associated with Galileo's letter of 29 November 1602 to Guido Ubaldo. These first two groups of notes do not explicitly refer to accelerated motion, and should not be assumed to do so implicity, where such an assumption can be avoided.

For French chemistry the early 1770's were lively years of discovery and controversy. Two neglected areas of research were opened up in 1772 with the publication of the Digressions académiques by Louis-Bernard Guyton de Morveau and with the first knowledge of later British pneumatic chemistry. Guyton's book established the general fact of weight-gain in metals upon calcination, thereby raising the problem of reconciling this gain with simultaneous loss of phlogiston. The spread of pneumatic chemistry, which proceeded rapidly in 1773, stimulated a renewed interest in the nature of air and its part in chemical composition. It was, of course, Antoine Laurent Lavoisier who perceived a relationship between these two developments—one which he believed would revolutionize the current understanding of chemical processes. In 1772 Lavoisier began the series of investigations which culminated in his Opuscules physiques et chimiques (1774), in which he demonstrated that weight-gain in both calcination and combustion is correlated with absorption of an equal weight of air.

In recent years a number of scholars have argued that Faraday's theories of matter and force were founded on concepts which were derived from Boscovich's Theoria Philosophiae Naturalis (1758). The notion that Faraday's ideas display Boscovichean tendencies is not a new one: it was proposed by several of Faraday's immediate successors and has been noted by more recent commentators. Statements of this kind are not implausible as assertions of a general correspondence between Faraday's views on matter, as expressed in the “Speculation touching Electric Conduction and the Nature of Matter” of 1844, and Boscovich's theory of point atomism, but Professor L. Pearce Williams has made much stronger claims for the dependence of Faraday's ideas on Boscovich's theory of matter. Williams' interpretation has been questioned by recent scholarship, and in this paper I wish to advance an alternative interpretation of Faraday's ideas on electricity and the nature of matter.

Research on thermal “black-body” radiation played an essential role in the origin of the quantum theory at the beginning of the twentieth century. This is a well-known fact, but historians of science up to now have not generally recognized that studies of radiant heat were also important in an earlier episode in the development of modern physics: the transition from caloric theory to thermodynamics. During the period 1830–50, many physicists were led by these studies to accept a “wave theory of heat”, although this theory subsequently faded into obscurity.

Proclaiming Louis Pasteur as the “Founder of Stereochemistry”, the distinguished Scottish chemist, Crum Brown, addressing a late nineteenth-century audience of Edinburgh savants, drew attention—as Pasteur had incessantly done—to the intimate relationship between living organisms and the optical activity of compounds sustaining them. It seemed to Crum Brown “that we must go very much further down in the scale of animate existence than Buridan's ass, before we come to a being incapable of giving practical expression to a distinct preference for one of two objects differing only in being one to the right and the other to the left”. Crum Brown's lecture must have been entertaining, but it was also motivated by a serious desire to do justice to a particular assertion of Pasteur—an assertion which had, moreover, been misunderstood and dismissed by no less a chemical genius than Wilhelm Ostwald. Writing at a time when the majority of his colleagues were stressing the resemblances between inorganic and organic compounds, Pasteur had insisted that he “could not point out the existence of any more profound distinction between the products formed under the influence of life and all others” than that “artificial products have … no molecular asymmetry”. Pasteur was obliged to concede that the chemist might produce enantiomorphic pairs of isomers, but without resorting to a manual separation of crystals he was powerless to imitate Nature's performance, powerless to fabricate by chemical means a separate optical isomer, divorced from its partner. Now it was not only Crum Brown who felt that chemists had brushed aside this proposition of Pasteur. In his 1898 Presidential Address to the chemical section of the British Association, Professor F. R. Japp also complained that the possible vitalistic implications of Pasteur's distinction between natural and artificial products had been misapprehended or tacitly ignored.

The modern corpuscular theory of radiation was born in 1905 when Einstein advanced his light quantum hypothesis; and the steps by which Einstein's hypothesis, after years of profound scepticism, was finally and fully vindicated by Arthur Compton's 1922 scattering experiments constitutes one of the most stimulating chapters in the history of recent physics. To begin to appreciate the complexity of this chapter, however, it is only necessary to emphasize an elementary but very significant point, namely, that while Einstein based his arguments for quanta largely on the behaviour of high-frequency black body radiation or ultra-violet light, Compton experimented with X-rays. A modern physicist accustomed to picturing ultra-violet light and X-radiation as simply two adjacent regions in the electromagnetic spectrum might regard this distinction as hair-splitting. But who in 1905 was sure that X-rays and γ-rays are far more closely related to ultra-violet light than to α-particles, for example ? This only became evident after years of painstaking research, so that moving without elaboration from Einstein's hypothesis to Compton's experiments automatically eliminates from consideration an important segment of history—a segment in which a major role was played by William Henry Bragg.

This paper sets out to examine the changes which took place in Thomas Young's concepts of the ether between 1799 and 1807. During the earlier part of this period he supposed the ether to consist of mutually repelling subtle particles which are attracted to particles of matter. Hence, he considered that the ether is denser within dense bodies than in rare ones. Furthermore, Young proposed that the ether density does not change abruptly at an interface; instead the denser ether extends beyond the geometrical limit of a body to form an atmosphere around it. As this hypothesis of an atmosphere of dense ether surrounding material bodies will be the central subject of this paper, I shall in future refer to it as the ether distribution hypothesis.

Ciliary motion refers to the activity of cilia, which are hairlike structures protruding from the surface of certain epithelial cells widely found in the animal kingdom. The main function of the currents produced by ciliary beating is the moving of fluid and small particles over the ciliated surface. It is now more clearly recognized that the study of cilia is contributing to the fundamental understanding of contractility and in this way is also helping to elucidate the mechanisms associated with muscular contraction, amoeboid and intracellular movements.

In 1864 nine eminent scientists, who had long been intimate friends, formed a dining club in order to prevent their drifting apart due to their various duties, and in order to further the cause of science. The club, which acquired the title of “X Club”, held monthly meetings from October to June, and was extremely active for two decades, but then gradually lessened in vitality. It served as a highly significant fraternity of scientists, and the regular communication which it afforded helped the members to marshall their efforts on behalf of science against what they felt to be the obstructionist activities and ideas of conservative scientists, certain theologians, and non-scientific society figures.

It is a matter of record that Henri Poincaré never responded publicly to Einstein's Special Theory of Relativity (RT). Since almost no private papers of Poincaré are available, his attitude toward Einstein's work and his silence on that score become somewhat of a mystery. It is almost certain that Poincaré knew of Einstein's work in RT. First, he was fluent in German, having learned it as a young man when the Germans occupied his home town of Nancy in 1870. Second, he often reported to the members of the Académie des Sciences on current work in electrodynamics in Germany. It is highly improbable that he would have missed the abstract of Einstein's first paper on RT or the subsequent articles by Einstein on the subject, especially those which were translated into French, since they were in areas directly related to his own interests in theoretical physics.