138 Miscellaneous Intelligence. 
been successfully worked, the pressure of steam is 2100 lbs. the 
square inch, while that of the air is optional, being regulated by a 
density at which the air is employed. 
In the second section, the various causes of waste of heat and ate 
in steam-engines are classified, and the actual efficiency of steam-en- 
gines is compared with their maximum theoretical efficiency, and also 
with the maximum actual efficiency, which may reasonably be supposed 
to be —— = jae steam-engine, by means of any probable mechan- 
ical improve 
The fo lowe ae estimates of the consumption of bituminous coal 
os a cat quality, per horse-power per hour :— 
or a theoretically perfect engine ye ci: between such limits 
temperature as are usual in ngines 1.86 Ibs. 
2. Fora os acting steani-engine ame to the utmost prob- 
EMM on cece cece cree cee n cca caten seer esenesens 2.50. “ 
3. dr a well constructed ~ ae worked ordinary double 
actin ng engine , On an ay £00 © 
to the peesinstion of coal of the athe quality per horse-power per 
hour :— 
Actual Consumption. Oommpien. of a i 
rfect Eng 
ine oe: Feurvia ce ceo lbe. 0.73 ths. 
Engine, weer e 280° * 0.82 
ia is ‘eu vied that an air- ~~ has actually been made to work 
successfully, and to realize an econ my of fuel considerably sper 
limit to which it is probable t ihe economy of double-acting eek: 
engines can ever be brought. Stirling’s engine, as finally improved, 
as pact in its dimensions, easily worked, not liable to get out 0 
order, and consum oil, and required fewer repairs than any 
Stirling’ S air-engine, as com a with a theoretically perfect ait- 
engine, sauee two-thirds of its fuel, and Ericsson’s somewhat more. 
Two obvious and powerful causes of that waste of fuel are traced—l. 
Deficiency i in extentof heating surface. 2. The communication of heat 
the furnace to the working air at those periods of the stroke whe2 
it is not performing work. 
The necessary conclusion is, that the more completely we remove 
those two causes of waste of fuel, the more nearly shall we apnrens 
mate to the theoretical extent of the econom my of the air-engine—an ex 
