On another page we have published two short letters, both agreeing as to the cause ot the explosion of the Blast Pipe at the Lehigh Crane Iron Works. The annexed letter is from one on the spot, who gives an account of the explosion and the cause, which nearly agrees with the opinions expressed in the two letters on the page spoken of. -MESSRS. EDITORS—The cause of the accident at the Lehigh Crane Iron Works, was on account of leaving a valve open between the tuyeres and the blast pipe, when the engine and furnace had been stopped about 30 or 40 minutes. The iron was run out a little after 8 o'clock, and the accident took place at 9. Gas returned through the valve, was ignited, and exploded. The only safe way to prevent the occurrence of such an accident is to have a pressure of air always against the valve, and to have the valve near the tuyeres. The accident interrupted the works for three weeks ; it was serious, but nothing like what was represented. About 220 tons of iron are made per week. The furnace is near 60 feet high, with an 18 feet bosh. The smallest movement of the bellows will keep back the gas, but when the engine is stopped it is necessary that all communication with the pipe and fires should be closed tight. *. *.