256 APPENDIX B. 



has often led to grave errors. Engines originally 

 well conceived have deteriorated in the hands of 

 unskilful' builders, who, wishing to introduce in 

 them improvements of little value, have neglected 

 the capital considerations which they did not know 

 enough to appreciate. 



NOTE H. The advantage in substituting two 

 cylinders for one is evident. In a single cylinder 

 the impulsion of the piston would be extremely 

 variable from the beginning to the end of the 

 stroke. It would be necessary for all the parts by 

 which the motion is transmitted to be of sufficient 

 strength to resist the first impulsion, and perfectly 

 fitted to avoid the abrupt movements which would 

 greatly injure and soon destroy them. It would 

 be especially on the working beam, on the 

 supports, on the crank, on the connecting-rod, 

 and on the first gear-wheels that the unequal 

 effort would be felt, and would produce the 

 most injurious effects. It would be necessary 

 that the steam-cylinder should be both sufficiently 

 strong to sustain the highest pressure, and with 

 a large enough capacity to contain the steam 

 after its expansion of volume, while in using two 

 successive cylinders it is only necessary to have 

 the first sufficiently strong and of medium ca- 

 pacity, which is not at all difficult, and to have 



