built and patented, in 1876 a very light steam boiler weighing from 39 to 44 lb. to the horse power, which appears to have been the prototype of some of the light boilers which have since been constructed. It consisted in a series of very thin tubes less than 1/8 in. in internal diameter, through which water circulated very rapidly, and was flashed into steam by the surrounding flame."

This type of boiler, which boils the water instantly, has come to be known as a flash boiler. The engine