The thermal fluctuations in radiation are described by the Einstein-Fowler relation $〈{\left(\Delta E\right)}^2〉=k{T}^2\left(\frac{\partial 〈E〉}{\partial T}\right)$. Two terms contribute to this fluctuation, a photon shot noise term and an expression predicted by wave theory. In the present experiment the second term has been measured.

• Received 20 June 1960

DOI:https://doi.org/10.1103/PhysRev.120.1551