386 THE SCIENTIFIC PAPERS OP 



and costly, and the duty performed by the 700 of heat is to give 

 them onward motion in the direction of the furnace. The hot 

 gases rising in the uptake represent a column of heated gas at a 

 temperature of 700, at which its density will be about half the 

 density at ordinary temperature. From the uptake they pass 

 through a long tube of sheet iron or steel, and on their journey 

 through this horizontal tube they part with most of their heat, 

 so that when they reach the downtake their temperature has 

 probably fallen from 700 to 200, having parted with 500 of 

 heat by radiation from the tube. The consequence is that the 

 descending column will be of about twice the specific weight of 

 the ascending column, and therefore a continual flow of the gas 

 will take place, ascending on the one side, and descending on the 

 other in forcing its way towards the gas furnace ; by this means 

 the heat apparently lost in the gas is utilized to produce useful 

 mechanical effect. 



But suppose that the gas passed from the producer to the 

 furnace without being allowed to cool, what would be the result ? 

 The gas would enter the regenerative chamber at a temperature 

 not of 200 but of 700 ; it would, in ascending, take up more 

 heat and enter the heating chamber at the temperature previously 

 imparted to the upper ranges of the chequer work by the 

 descending current or product of combustion. The same tem- 

 perature would be attained by the gas if it entered at 200*, the 

 only difference being that the regenerator in the case of the cooled 

 gas would work through a greater range of temperature by 500". 

 But a regenerator will work with the same economy through a 

 greater range as through a less range ; therefore, this heat, if it 

 could be saved, would be of no benefit whatever to the gas 

 furnace. The only difference in result would be that the gases 

 would get less cooled in descending on their way towards the 

 chimney, and that we should have a hot chimney instead of a 

 comparatively cool one. Therefore, no loss to the furnace is in- 

 curred in cooling the gas on its way to the regenerative chambers, 

 and the temperature of the gas is utilized to produce the very 

 essential mechanical effect of urging the gas from the producer to 

 the furnace. 



The economical action of the furnace depends upon the circum- 

 stance that the products of combustion reach the chimney, not at 



