The phenomena observed by M. M. Clement and Désormes, respecting a flat plate being sustained by escaping air instead of being forced away by it, will not have a sensible effect on the escape of steam by a safety valve, if it produces any; for it appears, from some trials I have made, that the plate must be considerably larger than the aperture to produce the effect, and this is not the case in those valves. M. Hachette's illustration and explanation of the phenomena, has been given by Mr. Brande, in his New Series of the Quarterly Journal of Science, Vol. II. p. 193.

Page 333, (art. 660.) I am indebted to Mr. Edward Deas Thomson, who has just returned from America, for the following account of one of the latest and the best boats they have constructed in the United States. "The • North America,' built by Kemble and Co. of New York, under the direction of Mr. Stevens, the owner,

The usual force of the steam is nine inches of mercury above the atmosphere, the extreme force fourteen inches, and the two engines consume two cords of wood per hour. The passage from New York to Albany is about 160 miles, and is performed at an average in twelve hours, with a consumption of twenty-five cords of wood. The boilers are placed before, and the machinery abaft the paddle wheels.”

I find by Bull's Essay on Fuel (Philadelphia 1827,) that a cord of wood weighs about 3826 lbs; and as the engines are of eighty-five horses' power, this gives forty-five pounds of wood per hour for each horse power. The ratio of coal to wood is (art. 190,) 8.22 to 22-6, according to which the equivalent quantity of coal would be 16.4 pounds.