and the Economy of Fuel. 67 



experiments made at different times and in different 

 seasons of the year, as the temperature of the water 

 in the boiler when the fire is lighted under it is seldom 

 the same in any two experiments, and as the boiling 

 heat varies with the variations of the pressure of the 

 atmosphere, or of the height of the mercury in the 

 barometer, it became necessary to make proper allow- 

 ances for these differences. This I thought could best 

 be done by determining, by computation, from the 

 number of degrees the water was actually heated, and 

 the quantity of fuel consumed in heating it that num- 

 ber of degrees, how much fuel would have been 

 required to have- it heated 180 degrees, or from the 

 point of freezing to that of boiling water (the boiling 

 point being taken equal to the temperature indicated 

 by 212 of Fahrenheit's thermometer, which is the 

 boiling point under the mean pressure of the atmos- 

 phere at the surface of the sea). Then, by dividing 

 the weight of the water used in the experiment (ex- 

 pressed in pounds) by the weight of the fuel expressed 

 in pounds necessary to heat it 180 degrees, or from 

 the temperature of freezing to that of boiling water; 

 this gives the number of pounds of ice-cold water 

 which (according to the result of the given experi- 

 ment) might have been made to boil, with the heat 

 generated in the combustion of i Ib. of the fuel, under 

 the mean pressure of the atmosphere at the level of the 

 surface of the sea. 



The city of Munich, where all the experiments were 

 made of which I am about to give an account, being 

 situated almost in the centre of Germany, lies very high 

 above the level of the sea. The mean height of the 

 mercury in the barometer is only about 28 English 



