(Bessel) (Legendre) . . (Hankel) . (Laplace) ∆V = 0 (x, y, z) n (r, θ, ϕ) rn fn(θ, ϕ) . fn(θ, ϕ) n fn(θ, ϕ) z = cos θ z θ ϕ 0 n ν . Pν(z), Qν(z) (Fourier) (Fourier Bessel) . . V ρ(x, y, z) ∆V = 4πGρ G : . (Poisson) . ρ = 0 V ∆V = 0 . . t (x, y, z) T(x, y, z, t) T ∂T ∂t = κ∆T κ . . ∂T/∂t = 0 ∆T = 0 . . . . i 1 1 1.1 . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.2 . . . . . . . . . . . . . .