Measurements are reported of the angular dependence of intensity and spectral width of light scattered quasielastically from three coexistent liquid phase α, β, γ near a tricritical point. From the data, the susceptibilities χ and correlation lengths ξ in each of the phases were calculated. Two predictions from mean‐field theory were tested, namely ’’Griffiths’ first sum rule’’: χα1/2+χγ1/2 =χβ1/2 or ξα+ξγ=ξβ, and ’’Griffiths’ second sum rule’’: χα−1/2+χγ−1/2−χβ−1/2∝ (T−Ttr), or ξα−1+ξγ−1−ξβ−1 ∝ (T−Ttr). The second sum rule is found to hold within the accuracy of our data. The first sum rule is violated for the correlation lengths. It is found to hold for the susceptibilities, but only after the scattered intensities are properly corrected for differences, between phases, in the derivative of the dielectric constant with respect to order parameter. This derivative was obtained from model calculations of Kaufman and Griffiths. The viscosities of the coexisting phases were measured; combined with the spectral width and correlation length data, they confirmed, with no adjustable parameters, Kawasaki’s equation for the Rayleigh linewidth of a critical fluid.