| 摘要 |
It comprises at least one nozzle (2A, 2B) for spraying water, means (3, 15, 17, 18B, 20A) for driving the nozzle to and fro along a predetermined trajectory, and means (31) which supply water to the nozzle and are designed to vary, in a predetermined cyclical manner, the strength of the jet emitted, over at least a part of the said trajectory. <IMAGE>
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