LOCOMOnVE ENGINE AND EAILTVAY GRADIENTS. 153 



taking the mean of Lardner's, Wood's, and Pambour's 

 experiments, it will be found to approximate to nearly 

 6 lbs. per ton : and, in the absence of more detailed and 

 more extended experiments, it will not be improper to cal- 

 culate the forces necessary for ascending steep gradients on 

 the supposition of 6 lbs. per ton being the resisting force 

 per ton of a railway carriage. 



Lastly. The resistance of the air, which is again variously 

 estimated. 



By Pambour, the resistances are given on every square 

 foot of surface, as follows :— 



At 20 miles aa hour 107 lbs. 



22 „ ,y ....i, ...... ..,.., x'oO ,f 



24 „ „ 1-65 „ 



26 „- „ 1-82 „ 



28 „ ,) ......... ^ 2"11 ,f .. 



30 "„ „ 2-42 ,* „ 



32 „ „ 2-75 „t. 



84 ,/ „ 311 ^.. 



36 „ „ 3-48 „ . 



38 „ „ .... 3'88 „ 



40 „ „ 4-30 „ 



42 „ „ 4-74,, 



44 „ „ 5-20 „ 



46 „ „ 5-69 „ 



48 „ „ 619 „ 



50 >. » 6-72 „ 



Mr. Woods makes the resistance, on a calm day, at a 

 velocity of 33 miles an hour, equal to ^ of the whole 

 weight, or 25'16 lbs. per ton; and taking 6 lbs. for friction, 

 we then have 25*16 — 6 n: 19 lbs. per ton for the resis- 

 tance of the air at 33 miles an hour. 



In Pambour, we have at 33 miles a resistance of 2*93 lbs. 

 per square foot ; and, supposing the area of surface exposed 

 to the action of the atmosphere to be 40 feet, it then fol- 

 lows, that 40 X 2-93 =: 117-2 lbs., the resistance of the air 



X 



