248 EIGHTH REPORT — 1838. 



would have, in a greater or less degree, the same effect upon the 

 air as the bow of a ship has upon the water through which it 

 is carried. 



The second is, that under such circumstances the moving 

 power acts from behind against the resistance, in the same man- 

 ner as an engine acts when used to push the train from behind 

 instead of drawing it ; that thereby the coaches composing- the 

 train are thrown out of square, and tlie resistance from flange 

 friction, and other causes consequent on such derangement, is 

 increased, and is the main cause of the excessive amount of re- 

 sistance whicli has been found in these experiments. 



To the first of these objections it may be answered, that the 

 engine and tender placed in front of the train increase the 

 amount of the transverse section by which the air is displaced 

 in the motion of the train ; the tire-box and ash-pit extend 

 nearly to the ground, and fill a space which is left almost open 

 in the absence of the engine ; the chimney rises above the roof 

 of the carriage and produces a resistance which has no existence 

 in the absence of the engine ; the head of the engine is usually 

 flat, and so far as it is concerned produces as much resistance 

 as an equal extent of flat surface upon the foremost end of 

 the coach. The tender which follows the enghie presents a 

 concave form to the air, a form considerably more adapted to 

 produce a resistance than the flat end of the carriage which it 

 intercepts. 



Up to the period of writing this report no opportunity has 

 been presented to the committee of ascertaining the force due 

 to this objection by direct experiment ; but it is intended to 

 place an engine and tender in front of a train, disconnecting 

 the working machinery, -so that the engine shall have no other 

 resistance than a coach of equal weight and similar construction, 

 and to repeat the experiment with the engine and tender so 

 placed. It will then appear how far the resistance will be mo- 

 dified by the form of the engine dividing the air in front. 



To the second objection it may be ansvvered, that the case of 

 the train moving by gravity down an inclined plane is not analo- 

 gous to that of an engine pushing a train behind. In the latter 

 case the whole power of the impelling force acts against the end 

 of the last carriage, Avhile the resistances which it has to overcome 

 have their position in the moving parts of each individual car- 

 riage, and in the frontage exposed to the resistance of the air. 

 But in the case of a train descending an inclined plane by gravity 

 neither the whole moving force nor any part of it acts against 

 the back of the hindmost carriage : the moving force, being the 

 gravitation of the matter composing the several carriages, will 



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