266 Meeltanics, t)hyslc,, and Chemistry.

]TIere it may be noticed that the difference between the steel plates of series C, and the iron plates of series A, is not considerable, though ia all others the steel plates exhibit a superiority in statical resistance.

(To be Continued.)

J[e~rdenlng Iron and Steel. ~'rom t]w London Builder, .No. 1015.

Mr. E. Partridge, of tile Patent Axle Works, Smethwlck, !las pro- visionally specified an invention which consists in first heating the ar- ticle to be hardened in a bath of lead or other suitable molten metals, or in a retort, so as to be protected from the direct action of fire. Irt applying to it, either in the bath or retort, or immediately on its with- drawal therefrom, a composition presently to be described, either in powder or liquid, in some cases the article is returned to the bath or retort after such application. In preparing the composition, he takes prussiate of potash or other substance containing cyanogen, or pos- sessing like chemical properties, and reduces it to powder. He mixes ~vith it powdered nitre and common salt, and sets fire to the composition; t i e takes the resulting ashes or substance remaining after the firing, and pew.tiers it. Tlle powder liquefies under heat, and he uses it alone or mixed with charcoal (animal or vegetable), or ott~er suitable form of carbon; or he liquefies the powder by dissolving it in liquid ammoni~ or other suitable solvent, and applies it to the articles to be hardened in a liquid state.

.Lecture on Torce. ]By Prof. TYNDALL, at the Royal Institution. From tile Lomlon Mechanics' Magazine, July, 1862.

The existence of the International Exhibition suggested to our hon- orary Secretary the idea of devoting the Friday evenings after Easter of the present )'ear to discourses oil the various agencies on which the material strength of England is based. I te wished to make iron, coal, cotton, and kindred matters, the subject of these discourses; opening the series by a discourse on the Great Exhibition itself; and he wish- ed me to finish the series by a discourse on " F o r c e " in general. F o r some months I thought over the ~ubject at intervals, and had devised a plan of dealing with it ; but three weeks ago I was induced to swerve from this plan, for reasons which shall be made known towards the conclusion of the discourse.

We all have ideas more or less distinct regarding force ; we know in ,~ general way what muscular force means, and each of us would less willingly accept a blow Dora a pugilist than have his ears boxed by a ]ady. But these general ideas are not now sufficient for us ; we must learn how to express numerically the exact mechanical value of the two blows; this is the first point to be cleared up.

A sphere of lead weighing i lb. was suspended at a height of 16 ft. above the theatre floor. I t was liberated, and fell by gravity. Tha~