The disk is now moved successively to positions 3, 4, 5, and so on. If we had a measuring device to determine the push against the disk at the various positions, it would be found that there is a point at some distance from the end of the pipe, at which the steam has the greatest striking force, which might be called the focal point.
A blow pipe exhibits this same phase; the hottest point is not at the end of the pipe, but at an area some distance away, called the focal point of heat.
The first feature of value, therefore, is to understand that pressure can be converted into velocity, and that to get a great impact force, the steam must be made to strike the hardest and most effective blow.
When a jet of steam strikes a surface it is diverted or it glances in a direction opposite the angle at which it strikes the object. In directing a jet against the blades of a turbine it is impossible to make it strike squarely against the surface.