EXPLANATION OF THE PLATES. 351 



There will, I think, be some advantage in making the pistons act together, 

 becavise the effect will be as great as by dividing it, supposing both methods to be 

 perfect ; and in acting together, there would be less interference of the motion of 

 the one with that of the other. The slide would be best moved from curved teeth 

 on the beams. See art. 481. 



For the proportions and construction of the boiler, see art. 244, 227, 278, and 

 522 526; for the engines, see art. 271 380; and for the power required, see 

 art. 590. 



