All engines of this character must run at a slow speed, for the reason that air does not absorb heat rapidly, and sufficient time must be given to heat up and expand the air, so as to make it effective.
Adhesion Engine.—A curious exhibition of the action of a gas against a solid, is shown in what is called an Adhesion Engine. [Fig. 117] shows its construction. A plurality of disks A are mounted on a shaft B, these disks being slightly separated from each other.
The steam discharge pipe C is flattened at its emission end, as shown at D, so the steam will contact with all the disks. The steam merely contacts with the sides of the disks, the movement of the steam being substantially on the plane of the disks themselves, and the action sets up a rapid rotation, and develops a wonderful amount of power.
It will be understood that the disks are enclosed by a suitable casing, so that the steam is carried around and discharged at a point about three quarters of the distance in the circumference.
This motor is given to illustrate a phase of the subject in the application of a motor fluid, like steam, or heated gases, that shows great possibilities. It also points out a third direction in which an expansive fluid may be used.
Thus the two well-known methods, namely, pressure, and impact forces, may be supplemented by the principle of adhesion, in which the expansive force of a gas, passing alongside of and in contact with a plain surface, may drag along the surface in its train.
Such an exhibition of force has an analogy in nature by what is known as capillary attraction, which shows adhesion. For instance, sap flowing up the pores of trees, or water moving along the fibers of blotting paper, illustrates movement of liquids when brought into contact with solids.