Quarto. [2], 5pp, [1]. Stitched as issued. Occasional light browning, some slight chipping to leaf margins, ink stamps to title and final blank page of the Plinian Society Edinburgh, a University institution for students with an interest in natural history, of which Charles Darwin was once a member.

A brief lecture delivered at the Royal Society of Edinburgh on 17th December 1827 by chemist and later master of the Royal Mint Thomas Graham (1805-1869). It is 'Graham's Law', first proposed in 1831, that explains the rate of diffusion of a gas - said rate being inversely proportional to the square root of the substances density.