This four-volume collection of primary sources examines scientific methodology in Britain during the long nineteenth century. As the physical, biological, human, and social sciences were radically reshaped across the 1800's, so the prevailing understanding of scientific methodology changed with them, making this period one of the most significant in the early development of the philosophy of science in the English-speaking world. This development was driven not only by the reflections of numerous men of science, scattered across their works, but also by the publication of some of the first major treatises in the philosophy of science. These volumes form a valuable complement instruction and learning in nineteenth-century philosophy and the history of science. An understanding of the philosophical and methodological innovations that grounded these epoch-making developments in the sciences is crucial for helping us understand how several generations of scientists interpreted and hoped to justify their own work. These same questions would go on to form a significant part of the foundation for reflection on such issues across the twentieth century and today.