The Philadelphia Orchestra was rehearsing Stravinsky’s Rite of Spring with incoming music director Christoph Eschenbach yesterday in its beautiful new concert hall, when strobe lights began to flash and dust started to drift down from above. Then, the downpour began. A high-powered sprinkler system, set off by construction work elsewhere in the building, engaged, and showered the musicians, their instruments (many valued at hundreds of thousands of dollars,) and the new stage with enough water to fill the $75,000 Steinway grand that sat on the stage. The extent of the damage is not yet known, but most musicians managed to shield their instruments from severe damage.