In these letters to Caroline Watts, a young friend and teacher in Durham, England, Spencer writes principally about the teaching of geometry and astronomy. He also comments on current political and literary events in England, including John Bright's defeat, the Corn Laws, and theories about health and religion. There is frequent mention of his brother Thomas Spencer, and his son Herbert Spencer.

Trained at Cambridge, the botanist Charles Baron Clarke (1832-1906) entered the English colonial civil service in 1865 as inspector of schools in Bengal. Over the course of the ensuing twenty-two years, he traveled extensively in Bengal, Assam, Kashmir, Nepal, and Bhutan collecting and meticulously documenting the native flora, constructing a massive herbarium that was eventually given to the Royal Botanical Gardens at Kew. He was author of several monographs and papers on the botany of the English colonies, and at different times in his career turned his pen to discussions of ethnology, education, political economy, and Indian music. For his varied efforts, he was elected a fellow of the Royal Society, the Linnaean Society, and the Geological Society.