John Murray (1785-1851), a writer and lecturer on many different scientific topics, published this collection of essays, on what might be called the physics of biology, in 1826. The first essay, on the luminosity of glow-worms, begins with an extensive discussion of the beauty and effects of light, and the various ways of creating it, before considering the various theories of light and optics current at the time. Supplied with specimens from Sweeney Hall in Shropshire, where they flourished, he performed various experiments on the 'luminous spherulae' which were the source of the glow-worm's light, trying to establish their chemical composition, and the time they would remain glowing in different media and temperatures. The same attention to detail and ingenious analysis are shown in the other studies, on the luminosity of the sea, the strength and lightness of spider webs, the chameleon's colour changes, and 'the torpidity of the tortoise'.