I can only imagine that it is an array of nozzles, quite possibly "en quinconce". Like an agricultural harrow or that spiked device the gendarmes put across roads that will puncture all your tyres in one go if you don't stop.

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Note added at 22 mins (2007-04-16 08:10:36 GMT)
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Grid?

The presently accepted test for watertightness of railcars involves locating the railcar in a waterspray booth (such as a car washer), where an ARRAY OF NOZZLES sprays water on the railcar
http://www.freepatentsonline.com/5780722.html

Use a rain facility capable of producing falling rain at the rate specified herein. To produce the rain, use a water distribution device that produces droplets having a diameter range predominantly between 0.5 mm and 4.5 mm. Ensure the rain is dispersed completely over the test item when accompanied by the prescribed wind. A water-soluble dye such as fluorescein may be added to the rainwater to aid in locating and analyzing water leaks. For steady-state rain, use either spray nozzles or the apparatus shown on figure 506.4-1 (with the polyethylene tubing removed), and position the dispenser at a height sufficient to ensure the drops approach terminal velocity. It is not necessary to use de-ionized or distilled water for this test
http://www.dtc.army.mil/pdf/810f-change2.pdf

Problems of State-of-the Art Water-tightness Performance Test Methods ... surface by a GRID of multiple nozzles spaced at a fixed distance between them. ...
tingwall.com/articles/article_06.html