A collection of brief lectures and essays presenting and debating contemporary scientific ideas about life and the physical world. Contributors examine the physical basis of living matter, the relation between vital and physical forces, the nature and significance of protoplasm, and the hypothesis of evolution, while also reflecting on experimental methods, atmospheric phenomena, and the role of imagination in research. The pieces combine explanatory exposition, critical rejoinders, and methodological reflection to make scientific theories and controversies accessible to an educated general readership.