James Clerk Maxwell1831–1879- Introductory Lecture on Experimental Physics, Cambridge (October 1871), in The Scientific Papers of James Clerk Maxwell, ed. W. D. Niven (1890; Dover repr. 2003), vol. 2, p. 243
- Letter to Lewis Campbell (9 November 1851), in Lewis Campbell and William Garnett, The Life of James Clerk Maxwell (1882), ch. 6, p. 159
- “On Physical Lines of Force”, Part III (1862)





