THE FRICTIONAL EFFECT OF RAILWAY TRAINS 



UPON THE AIR.* 



Francis E. Nipher. 



The effect of any medium in retarding a body moving 

 through it, has been very carefully studied in connection with 

 moving ships and trains of railway cars, and in various other 

 ways. In train resistance it is well known that the effect 

 of the air is made up of end effects, and of side effects. The 

 end effects are the result of the compression at the head end 

 and the rarefaction at the rear end. These retarding effects 

 are independent of the length of the train. The side effects 

 are due to the viscocity of the air. They are in the nature of 

 a shear. The resistance to the train due to this cause, is 

 directly proportional to the length of the train. 



That the air in contact with the sides of a train has an 

 appreciable effect in resisting its motion, carries with it as a 

 necessary consequence, the dragging of air along with the 

 sides of the train. This phenomenon is well known. It has 

 lonor been known as a source of danger in connection with 

 fast trains. At least eighteen years ago the writer witnessed 

 with some surprise the frantic efforts of a station agent of 

 the New York Central Railroad to drive everybody from the 

 platform to the interior of the station building. The fast 

 train from New York was due, and it soon passed at full 

 speed. I declined to leave the platform, and discovered the 

 reason for his behavior when the train passed. The draught 

 of air which accompanied the train was sufficient to cause 

 serious alarm. The agent afterwards explained to me that 

 serious results might follow such imprudence as I had shown. 



* Presented, and read by title, at the meeting of The Academy of Science 

 of St. Louis, of October 16th, 1900. 



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