Abstract: A rain gauge having a collecting funnel and a discharged nozzle is provided with a detector for detecting the abstraction of a filter at the input of the nozzle. The detector comprises a light source disposed on an upper portion of said funnel and illuminating the bottom of the funnel above the filter. A sensor located outside of the funnel and nozzle, detects light which is reflected and diffused by the inner surface of the funnel and which passed through the filter and along the nozzle. The sensor is offset laterally with respect to the nozzle. An electronic box is connected to the source for causing the source to emit light pulses at regular time intervals and is connected to the sensor for detecting those output signals of the sensor which exceed a predetermined threshold.