apparatus for measuring the level of water in an enclosure . it comprises an assembly , which is constituted by a radiation source located in the vicinity of the enclosure wall , and n radiation detectors separated from the radiation source by a path traversing the enclosure and located at different levels on a same vertical line . after amplification , each detector supplies a signal proportional to the intensity of the radiation received . it comprises means for processing the signals supplied by the detectors , said means being constituted by n - 1 dividing circuits , the detectors being connected in pairs to a dividing circuit , which forms the quotient μ 1 / μ i + 1 , the level then being located in the gap between the detectors , for which the quotient μ i / μ i + 1 is maximum .