354 THE CANADIAN NATURALIST. [Vol. X. 



is luminous ; the hot products of combustion carry off at least 

 four times as much energy as is radiated, so that no more 

 than one-hundredth part of the heat evolved in combustion 

 is converted into light. This proportion could be improved, 

 however, by increasing the temperature of combustion, which 

 may be effected either by intensified air-current or by regenera- 

 tive action. Supposing that the heat of the products of com- 

 bustion could be communicated to metallic surfaces, and be 

 transferred by conduction or otherwise to the atmospheric air 

 supporting combustion in the flame, we should be able to increase 

 the temperature accumulatively to any point within the limit of 

 dissociation ; this limit may be fixed at about 2300"^ C, and can- 

 not be very much below that of the electric arc. At such a temper- 

 ature the proportion of luminous rays to the total heat produced 

 in combustion would be more than doubled, and the brilliancy of 

 the light would at the same time be greatly increased. Thus 

 improved, gas-lighting may continue its rivalry with electric 

 lighting both as regards economy and brilliancy, and such rivalry 

 must necessarily result in great public advantage. 



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 ques- 

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

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

 sider 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 result- 

 ing from imperfect installation, and these may be co completely 

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

 equivalent values of the two forms of energy. But in attempt- 

 ing 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 differ- 

 ence of temperature between the boiler and condenser. The 



