Before his untimely death from typhoid, William Spottiswoode (1825-83) had served as president of the London Mathematical Society, the British Association, and the Royal Society. In addition to publishing widely in mathematics and the experimental physical sciences, he restored the fortunes of his family printing firm, Eyre and Spottiswoode, the Queen's printers. An enthusiast for the popularisation of science, he lectured to large audiences at the Royal Institution, the South Kensington College of Science, and at British Association meetings. He also gave scientific talks at the school set up for the employees of his family firm. This illustrated 1874 work is based on these talks, and provides an introduction to 'this beautiful branch of optics'. Spottiswoode covers methods of polarisation, and the contemporary theory accounting for these effects. He describes various experiments, and explains how polarisation causes patterns and colours to appear in light.