WILLIAM SIEMENS, F.R.S. 341 



stove. Tin- advantages usually claimed for the open fireplace are, 

 that it is cheerful, 'pokable,' and conducive to ventilation, but to 

 these may be added another of even greater importance, viz., that 

 the radiant heat which it emits passes through the transparent air 

 without wanning it, and imparts heat only to the solid walls, floor, 

 and furniture of the room, which are thus constituted the heating 

 surfaces of the comparatively cool air of the apartments in 

 contact with them. In the case of stoves the heated air of the 

 room causes deposit of moisture upon the walls in heating them, 

 and gives rise to mildew and germs injurious to health. It is, I 

 think, owing to this circumstance that upon entering an apart- 

 ment one can immediately perceive whether or not it is heated by 

 an open fireplace ; nor is the unpleasant sensation due to stove- 

 heating, completely removed by mechanical ventilation ; there is, 

 moreover, no good reason why an open fireplace should not 

 be made as economical and smokeless as a stove or hot-water 

 apparatus. 



In the production of mechanical effect from heat, gaseous fuel 

 also presents most striking advantages, as will appear from the 

 following consideration. When we have to deal with the question 

 of converting mechanical into electrical effect, or vice versa, by 

 means of the dynamo-electrical machine, we have only to consider 

 what are the equivalent values of the two forms of energy, and 

 what precautions are necessary to avoid losses by the electrical 

 resistance of conductors and by friction. The transformation 

 of mechanical effect into heat involves no losses, except those 

 resulting from imperfect installation, and these may be so com- 

 pletely avoided that Dr. Joule was able by this method to deter- 

 mine the equivalent values of the two forms of energy. But in 

 attempting the inverse operation, of effecting the conversion of 

 heat into mechanical energy, we find ourselves confronted by the 

 second law of thermo- dynamics, which says, that whenever a given 

 amount of heat is converted into mechanical effect, another but 

 variable amount descends from a higher to a lower potential, and 

 is thus rendered unavailable. 



In the condensing steam engine this waste heat comprises that 

 communicated to the condensing water, whilst the useful heat, or 

 that converted into mechanical effect, depends upon the difference 



