627 When the jockey crouches over the neck of his race-horse, and when Tod Sloan introduced the ãAmerican seat,ã the object in both cases is to relieve the hind-legs of weight, and so leave them free for the work of propulsion. Nevertheless, we must not exaggerate the share taken by the hind-limbs in this latter duty; cf. Stillman, The Horse in Motion, p. 69, 1882.
629 The method of constructing reciprocal diagrams, in which one should represent the outlines of a frame, and the other the system of forces necessary to keep it in equiôÙlibôÙrium, was first indicated in Culmannãs Graphische Statik; it was greatly developed soon afterwards by Macquorn Rankine (Phil. Mag. Feb. 1864, and Applied Mechanics, passim), to whom is mainly due the general application of the principle to engineering practice.
630 Dialogues concerning Two New Sciences (1638): Crew and Salvioãs translation, p. 140 seq.
631 The form and direction of the vertebral spines have been frequently and elaborately described; cf. (e.g.) Gottlieb, H., Die Anticlinie der WirbelsûÊule der SûÊugethiere, Morphol. Jahrb. LXIX, pp. 179ã220, 1915, and many works quoted therein. According to Morita, Ueber die Ursachen der Richtung und Gestalt der thoracalen DornfortsûÊtze der SûÊugethierwirbelsûÊule (ibi cit. p. 201), various changes take place in the direction or inclination of these processes in rabbits, after section of the interspinous ligaments and muscles. These changes seem to be very much what we should expect, on simple mechanical grounds. See also Fischer, O., Theoretische Grundlagen fû¥r eine Mechanik der lebenden KûÑrper, Leipzig, pp. 3, 372, 1906.
632 I owe the first four of these determinations to the kindness of Dr Chalmers Mitchell, who had them made for me at the Zoological Societyãs Gardens; while the great Clydesdale carthorse was weighed for me by a friend in Dundee.