1891. The curved-barrel engine (fig. 504.) has the barrel and piston-rods curved so as to form part of a circle, &c. By this construction, the bore of the barrels may be formed in the lathe, and consequently made perfectly true: the piston-rods move exactly in the direction of the axis of the barrels, and, therefore, operate with the least possible friction. For a portable engine this is one of the best. Both these engines would receive great additional power, by adopting the improvements on the syringe by Read (1850.).