26 ANNUAL OF SCIENTIFIC DISCOVERT. 



" The new system of reversing steam has been, until recently, 

 limited to the use of a mixtun^ of steam and water. The ena;!- 

 neers to wiiom I had entrusted the task of making the first trials 

 followed my instructions with some apprehension, endeavoring as 

 much as j)ossible to avoid the injeetion of water into the cylinders. 

 The result has been that, even now, in Spain, where these lirst 

 trials were made, the use of counter-pressure steam has not had 

 the success which it has had elsewhere. In France, the part 

 played by tiie water was better understood; it has been abun- 

 ilanlly injected, and the results have been most satisfactory ; but 

 up to the moment when I iiad an opportunity of personally ex- 

 perimenting, in order to verify the correctness of my first concep- 

 tions, steam was universally considered as a necessary agent, and 

 was used in a greater or less proportion. It was supposed that 

 its function was to till the cylinders during the period of aspira- 

 tion, aiul that it served as the vehicle for the water which was 

 shut in with it, behind the piston, at the moment the period of 

 cushioning and foreing back commenced. It was supposed that 

 the water led from the boiler was applied directly to the absorp- 

 tion of heat. 



" I have shown that the water is converted into steam from the 

 moment that it enters the cyliniler, even during the period oi' as- 

 Ijirulion, and the conclusion is that not only is it not required to 

 take steam directly from the boiler, but that the addition of steam 

 to the water, beyond a certain limit, might become prc\judicial. 



" In every case the substitution of steam for, or the addition of 

 steam to, water results in a discharge of a less moist steam 

 from the cylinders into the boiler, and jt is the same with the 

 steam in the exhaust-pipe used for aspiration. The ruljbing sur- 

 faces aie therefore drier, and the friction greater. The more the 

 proportion of steam is increased, the more these cft'ects become 

 seiK<il)le. At last the steam actually diverts the water indispen- 

 s;).l)le for the absorption ot the heat, although large quantities of 

 steam escape l)y tlie funnel, anil although no gases from the 

 smoke-box get into the cylinders. 



*' The intervention of steam durinjjthe workins with inverse ad- 

 mission, unless required for some particular purpose, which- I 

 shall point out presently, is always more or less prejudicial. The 

 rule, in fact, should be, to add the least possible quantity of steam 

 to the water. The wet steam, on the water issuing from the 

 boih.'r, gives this minimum proportion. 



'• The apparatus to be fitted to the locomotive, to admit of work- 

 ing counter-pressure steam as a brake, is as simple as the princi- 

 ple itself. It consists of a tube of an inch to an inch and a quarter 

 in diameter, — one inch diameter is very convenient, — wliich com- 

 municates between the boiler and the exhaust- i)ipe, and a dis- 

 tributing cock by which the driver regulates the supply. If, as I 

 advise, although it is not indispensable, it is desired to hav(> the 

 power of inj<!cting watcu' and steam alternately or simultaneously, 

 a second cock is j)lac»'d, with a sliort tube as a branch from the 

 first, at a short distance from its origin. The one tube enters 



