IN connexion with an article on “Early Hydraulio Engineering”, in which the work of Clemens Herschel (1842-1930) is referred to, Engineering in its issue for August 2 reproduces a letter from Herschel to the late Dr. Unwin describing his invention of the Venturi Meter. The letter is dated June 5, 1888, and addressed from the hydraulic engineer's office of the Holyoke Water Power Co., Mass. In his letter, Herschel says ho tested a one-inch Venturi Meter, under 210 ft. head: “I am now satisfied that here is a new and pregnant principle to be applied to the art of gauging fluids, inclusive of fluids such as compressed air, illuminating or fuel gases, steam, etc. Further, that the shape of the meter should be trumpet-shaped in both directions; such a meter will measure volumes flowing in oither direction, which in certain localities becomes a useful attribute. . . . And we are but in the beginning of the art of measuring pressures, and differences of pressure. When these shall be delicately measured, the Venturi Meter will have become as delicate in its lower limits of capacity, as any other and it is on this score alone, that it is as yet inferior to some of the volumetric meters.” The letter was found among the papers placed at the disposal of the Unwin Memorial Committee by Miss Unwin.