408 Mechanles, -Physic#, and Chemistry.

as great ~ resistance as like bars subjected to a like defleetlon by sta- tical weight.

Of two bars subjected to a deflection equal to that carried by half of their statical breaking weight, one broke with 28,602 depressions, and the other bore 30,000 and did not appear weakened to resist sta- tical pressure.

Of a number of bars subjected to a vibratory depression, equal to the deflection due to a load of one-third of their statical breaking weight, one broke at 51,538 depressions, and one bore 100,000 with- out any apparent diminution of resistance.

Of three bars subjected to a like character of depression, equal to the deflection due to a load of one-half of their statical breaking weight, they broke at 490,617, and 900 depressions respectively.

Hence, cast iron bars will not bear the continual applications of one- third of their breaking weight.

A bar of wrought iron, 2 inches square and 9 feet in length between its supports, was subjected to 100,000 vibratory depressions, each equal to the deflection due to a load of five-ninths of that which per- manently injured a similar bar, and their depressions only produced a permanent set of "015 inch.

Three wrought iron bars were subjected to 10,000 vibratory depres- sions, depressing them through one-third, two-thirds, and five-sixths of an inch respectively, without receiving any perceptible permanent set.

A_ bar of wrought iron depressed through one inch received a set of • 06 inch, and one depressed 300 times through two inches received a set of 1"08 inch.

The greatest deflection which did not produce any permanent set was due to rather more than one-half the statical weight~ which per- manently injured it.

A wrought iron box girder, 6 X 6 inches and 9 feet in length, was subjected to vibratory depressions, and a strain corresponding to 3752 lbs. repeated 43,370 times, did not produce any appreciable effect on the rivets.

3~oom for Improvement in the 8team .Engine. From the London Engineer, No. 252.

The unit of heat is that which is sufficient to raise the temperature of one pound of water by 1 deg. of Fah. The unit of work is the raising of one pound weight through a vertical height of one foot-- called a foot pound. Tile experiments of Mr. Joule, of Manchester, indicated that if the whole of the heat could be rendered available, a unit of heat would raise 772 pounds 1 ft. high ; in other words, a unit of heat is equal to 772 footTounds. This is called Joule's equivalent. A pound of charcoal will raise 78"15 pounds of water 180 dog., which is equal to 14,067 units of heat. This multiplied by 772, gives 10,- 859,724 foot-pounds, which is equal to the production of 5½ horse pow- er from the combustion of 1 lb. of charcoal per hour. As the best en- gines consume nearly 2 lbs. of coal per horse power per hour, it follows that about only one-tenth part of the gross power of the fuel is utilized.