20 REPORT— 1882. 



advantages nslially claimed for the open fireplace are, that it is cliecrful, 

 * 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 transpai'ent air without warming it, and imparts heat only 

 to the solid walls, floor, and fui'niture of the room, which are thus con- 

 stituted the heating surfaces of the comparatively cool air of the apart- 

 ments 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 apartment 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 efiect from heat, gaseous fuel also 

 pi'esents most striking advantages, as will appear from the following con. 

 sideration. 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 efiect into heat involves no losses, except 

 those resulting from imperfect installation, and these may be so completely 

 avoided that Dr. Joule was able by this method to determine the equivalent 

 values of the two forms of energy. But in attempting the inverse operation, 

 of efi"ecting the conversion of heat into mechanical energy, we find our- 

 selves confronted by the second law of thermo-dynamics, which says, that 

 whenever a given amount of heat is converted into mechanical efiect, 

 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 efiect, depends ui3on the diS'erence of tem- 

 perature between the boiler and condenser. The boiler pressure is 

 limited, however, by considerations of safety and convenience of con- 

 struction, and the range of working temperature rarely exceeds 120° C. 

 except in the engines constructed by Mr. Perkins, in which a range 

 of 160° C, or an expansive action commencing at 14 atmospheres, 

 has been adopted with considerable success, as appears from an able 

 report on this engine by Sir Fredei-ick Bramwell. To obtain more ad- 

 vantageous primary conditions we have to turn to the caloric or gas engine, 



because m them the coefficient of efiiciency expressed by ■ may be 



greatly increased. This value would reach a maximum if the initial 



