1. H.C. Sorby, Journal, Iron and Steel Institute, No. 1, 1886, p. 140
2. F. Osmond, Journal, Iron and Steel Institute No. l, 1890, p. 38
3. Tschernoff, Imperial Technical Society, 1868
4. Arnold and McWilliam, Journal, Iron and Steel Institute, No. 2, 1905, p. 27
5. C. Benedicks, Journal, Iron and Steel Institute No. 2, 1905, p. 352