1. For an excellent critical survey, including an exhaustive list of references, seeL. G. Suttorp andS. R. de Groot:Physica,39, 84 (1968).
2. L. Rosenfeld:Mem. Acad. Roy. Belg.,18, No. 6 (1940);F. J. Belinfante:Physica,7, 449 (1940).
3. The covariant derivative in the first term of equation (1) is to be taken by holding the tensorsp α,S λμ fixed by parallel propagation. ThusN ¦β =∂N/∂x β −(∂N/∂p μ )Γ αβ μ p α−2(∂N/∂S λμ )Γ αβ [μ S λ]α. Note also that the equations of motion cannot in general be cast in Hamiltonian form, and the extended phase volume (−g)1/2 d4 xdΩ is not conserved. Conventions: space-time signature (+ + + −), Riemann and Ricci tensors defined by 2A λ¦[μν]=A α R αλμν,R λμ=R αλμα, square brackets denote antisymmetrization.
4. W. G. Dixon:Nuovo Cimento,34, 317 (1964);Proc. Roy. Soc., A314, 499 (1970); A319, 509 (1970).
5. J. Madore:Ann. Inst. Henri Poincaré,11, 221 (1969);L. G. Suttorp andS. R. de Groot:Nuovo Cimento,65 A, 245 (1970);H. P. Künzle:Comm. Math. Phys.,27, 23 (1972).