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THE FLOW OF SOLIDS.

When the metal was pressed througli more than one orifice inthe die, it was observed that the jets nearesfc the centre wererather larger than those near to the sides of the cylinder, thelesser effect being due to the friction of the sides. This differ-ence in pressure on different parts of a solid mass explains thedisplacements that take place in the inferior of the mass.

The experiinents established that the pressures exerted on thesurface of a solid body are transmitted throughout the wholeinterior of its mass, and tend to produce in it a flow whichis propagated from particle to particle, and which necessarilydevelops itself in the direction where the resistances to theflow are the least; also that the pressures thus transmitteddetermine in a fixed Order the changes of form at each point.Further, these changes of form are attended by a loss of pressurebetween one point and another, similar to, but even greaterthan, that in the case of the flow of liquids.

In the processes of rolling and forging iron, the observationsof M. Tresca have a practical value, as indicating the necessityfor the application of a pressure or blow sufficiently powerfulto reach the interior of the mass in Order to enable the metalto flow, and its fibrous continuity to be preserved.

The object which has to be attained in manipulating wroughtiron under a forging, bending, or other tool, is to dispose thefibres in the direction conforming to the purpose to which theiron is to be applied. Such disposition of the fibres or threadsin uniformly continuous lines ensures the strengtli of the massbeing preserved, whereas if the application of a blow results ina disturbance of this arrangement of the fibres (producing, as itwere, eddies in the flow of the particles), the power of resistanceis necessarily lessened.

The application of a squeeze by a hydraulic appliance, insteadof a blow by a steam-hammer, enables the Operation of stampingmetal to be performed with better regard to the preservation ofthe continuity of the particles. The shapes for the dies at thevarious stages of the work can be considered with reference tothe natural tendency of the metal to flow in the direction of the