Essays: Scientific, Political, & Speculative; Vol. 2 of 3 / Library Edition (1891), Containing Seven Essays not before Republished, and Various other Additions.

The essays examine the origins and methods of scientific knowledge, arguing that science extends perception through reasoning and progresses from qualitative to quantitative prediction; present a scheme for classifying the sciences and a critique of Comte's philosophy; analyze the nature and discovery of laws and how to weigh evidence; offer a clear account of electricity and engage in methodological debates over tests of truth with replies to critics; and address aesthetics, considering style, beauty, architectural types, gracefulness, personal beauty, the origins and function of music, and the physiology of laughter.