The sixth chapter of Charles Darwin’s Origin of Species is called “Difficulties of the Theory.” In that part of his work, Darwin reveals some possible objections to his theory and attempts to provide an answer to all of them. Such a chapter was part of the first edition of the Origin of Species; therefore, the difficulties described were not reactions derived from the publication of the book. Instead, friends like Charles Lyell have probably presented some of them. Others can be (...) found in works published before Darwin’s work, such as Natural Theology by William Paley, which argued for creationism and introduced arguments against any natural explanation of the origin of species. Many other problems dealt with in the sixth chapter were born, however, from Darwin’s own internal dialogue, his own initial doubts concerning the theory, and his anticipation of criticism, as one can gather from his manuscripts. This paper describes the main difficulties shown in the sixth chapter of the Origin of Species, providing a more detailed exposition of a few topics, and analyzing Darwin’s defense, in those cases. It also discusses some of the weak points in Darwin’s line of reasoning from a diachronic point of view. (shrink)

The focus of this paper is one of James Prescott Joule’s scientific contributions: the laws of heat production by electric currents in conductors. In 1841, the 22 years old Joule published a paper with the title “On the heat evolved by metallic conductors of electricity, and in the cells of a battery during electrolysis” where he presented an experimental study of that phenomenon and proposed two laws that were allegedly supported by his trials. On closer inspection, both his laboratory work (...) and his inferences can be challenged. The emphasis of this article is an attempt to understand Joule’s experimental undertaking, its highpoints and shortcomings, by a detailed analysis of this specific episode and by studying the precedents of his work and subsequent advancements. It is possible to point out several serious deficiencies of that investigation, and Joule’s contemporaries, such as Edmond Becquerel and Heinrich Lenz, did criticize some of his flaws and undertook new experiments to provide a sound basis for those laws. Besides providing a historical examination of that specific episode, this article uses this case study to tackle some features of the nature of science that may contribute to scientific education. (shrink)