573 TEANSAGTIONS OF THE 



To establish the best coal-burning boiler, is now the grand 

 desideratum, of locomotive engineering, ciu-ved, spiral, diagonal, 

 and branched water tubes, combustion chambers, and flues, ver- 

 tical tubes, and fire boxes of innumerable shapes, each develop, 

 with more or less success, some particular doctrine. The great 

 aim is the securing, with limited cost and repairs, an abundant 

 fire surface. The importance of such a change is fully apprecia- 

 ble to those who have seen its results in their own experience. 



It would appear, then, that the perfection of boilers, so long as 

 the water and the fire are separated, must be accomplished by 

 the better application of principles universally known, and at 

 least theoretically established. The importance of each of these 

 principles will contribute to almost incredible advantage in the 

 general result, while success is eminently promising. 



Use, or application, the second brancli of steam engineering, 

 having reference to the engine proper, is far advanced, but still 

 imperfect. Its history is also suggestive. 



The distribution and exhausting of steam, appeared most pro- 

 mising to its early employees, when the closing of a port, and the 

 passing of a centre, were the work of the same instant. But the 

 efficacy of the lap and the lead were soon apprehended and 

 demonstrated. These modifications of motion having amounted 

 to a fixed cut-off, the value of the three changes was found to 

 lie in somewhat opposite directions. An additional valve reme- 

 died this difficulty, and a variable independent cut-off, at first in 

 a separate chest, then on the main valve, completed the improve- 

 ments of this variety. The stationary link afforded a variable 

 cut-off with one valve, and the shifting link, with its variable 

 lead and cut-off, together with unequal steam and exhaust lead, 

 and the widening of ports, was at length almost universally 

 adopted. 



And it may not be inappropriate to remark, that the complica- 

 tion of its motions and principles, and the simplicity and dura- 

 bility of its parts, render the link-motion at once the most beautiful 

 and triumphant of mechanical combinations. 



These changes pomt to the principles which they have so dis- 

 tinctly developed and proved. 



To use steam with the greatest economy, 1st. The boiler pres- 

 sure must be preserved in the cylinder, to the point of cut-off. 

 2d. The exhaust must oppose no resistance to the return stroke. 

 3d. All friction, save that of joints and packing, must be omitted. 

 In detail, these laws should thus appear, viz : ample and smooth 



