284 OF THE APPLICATION [SECT. ix. 



worked ; other sized machines nearly in proportion to their breadth : this supposes 

 the machine to be well made and kept in tolerable order. 



The proper species of engine for farm use is the double engine (art. 414 

 and 419.) with slides, and the whole arranged in the most simple and obvious 

 manner. 1 



589. CORN MILLS. The mean quantity of power required to grind and dress 

 a Winchester bushel of wheat per hour is 31,000 Ibs. raised one foot per minute, 

 and the best velocity for the circumference of a millstone is twenty-three feet per 

 second ; and with this velocity a pair of five feet stones will grind from four to 

 five bushels per hour, according to their condition and the state of the grain : 

 the double expansive engine should be used for this kind of work ; and when 

 working to the best advantage with low pressure steam, it should grind 

 fourteen bushels of wheat for each bushel of coals, and the average should be 

 eleven bushels and a half for one bushel of coals. 2 The same species of engine 

 with strong steam will of course do more work with a given quantity of fuel. 

 (See art. 419.) 



OF THE APPLICATION OF STEAM POWER TO CARRIAGES. 



590. The application of a power within a carriage to move it, is a subject 

 that at an early period engaged the attention of speculative men. Some of their 

 schemes are described by Emerson in his ' Mechanics,' and he gives an example 

 of calculation there (Ex. 20. p. 194.) which seems to be very little understood. 

 The object of it is to determine the power required to move a waggon ; but in fact 

 it simply determines the relation of the forces, the power being the same whether 

 it be in the waggon or out of it, provided it does not add to the weight of the 

 waggon. But power cannot be gained without adding weight; and in steam 

 carriages the whole mass of the engine, with its boiler and fuel and water, has 

 to be moved as well as the load ; and in order to keep the engine as simple and 

 light as possible, and to avoid the weight of water and complexity of a condensing 

 apparatus, high pressure steam is always employed. 



The idea of employing steam as a moving power has been considerably 



1 If an engine be applied for irrigation, it may have the thrashing machine attached when the 

 situation is convenient ; but in that case a double engine should be used. 



2 For 6-5 Ibs. per hour is equal to a horse power, (art. 419.) and a bushel of coals being thirteen 

 times this quantity, it is equal to thirteen horse power per hour ; and 31000 : 33000 : : 13 : 14, 

 nearly. 



