1. G. Sarton, A History of Science, vol. 1., Harvard University Press, Cambridge, Mass. (1952).
2. J. Burnet, Early Greek Philosophy, Adam and Charles Black, London and Edinburgh (1892). p. 115.
3. M. Hesse, Forces and Fields: the concept of action at a distance in the history of physics, Nelson, London (1961), p. 31.
4. Diogenes Laertius, Lives of Eminent Philosophers (trans. R.D. Hicks), The Loeb Classical Library, Heinemann, London (1925), p. 27.
5. G.S. Kirk and J.E. Raven, The Presocratic Philosophers, Cambridge University Press (1971), p. 158.