On wave matrices, and some properties of the wave equation

1—Wave matrices became important in wave theory as the result of the use of them made by Dirac to express the operator of the second order wave equation as the square of a linear one, and hence obtain a first order equation. Thus, p 2 representing the second order operator, the equation p 2 Ψ = 0, may be factorized, and written (∑ E α p α ) (∑ E α p α ) Ψ = 0, (α = 1, 2, . . . , n ), giving the first order equation ∑ E α p α Ψ = 0, (1) if the p α commute with themselves and with the E α , and if the E α are matrix roots of +1 or of —1, which satisfy E α E β = — E β E a (β ≠ α). (2)