ON RAILWAY CONSTANTS. 



251 



tons. 



The weight of the train, exclusive of wheels and 1 , ^ . 



axles, was equal to J 



The weight subject to rolling motion, viz. the wheels \ „ , 



and axles, was J 



Total 



14.-8 



The radius of the wheels was 18 inches, and the distance from the centre 

 of the wheel to the centre of oscillation was 10 inches. In accordance with 

 these data, the quotient alluded to, page 249, must be corrected by multiply- 

 ing it into the constant number 1*09. 



Three Liverpool and Manchester First-class Carriages. 



At these slow velocities the atmosphere would not offer much resistance, 

 and we may therefore practically consider the resistances assigned to be those 

 of friction alone. One remarkable result will not escape the attention, viz. 

 that the resistance diminishes until the train attains the speed of 7*58 miles per 

 hour, after which it again increases, owing no doubt to the opposition of the 

 air at the higher mean velocity. At 4*32 miles per hour the resistance was 

 6"07 lbs., whereas at 7'58 miles per hour it becomes only 5*60 lbs. per ton, 

 showing a difference of ^ lbs. of a lb. per ton. This fact, it is believed, has 

 hitherto been unnoticed. The cause is owing to a more perfect lubrication 

 of the axles at the higher speed, and depends probably upon the formation 

 of a certain thickness of film of grease between the brass step and the upper 

 surface of the journal which keeps the two surfaces more effectually apart. 

 In consequence of the slow velocity the pressure of the step upon the journal 

 has a longer time to act in effecting the displacement of the fresh grease 

 which has been supplied from the box, and the result is a greater amount of 

 friction. 



We proceed to estimate the friction of the other description of carriages, 

 viz. those belonging to the Grand Junction Company, and which were used 

 in the experiments on the long planes of the Grand Junction Railway. 



On the evening of the 12th of July, 1839, a train of eight second-class 

 Grand Junction carriages, weighing gross iO-lS tons, was brought to the 

 top of the Sutton inclined plane, and allowed to descend from a state of rest 

 from the post numbered 0, as in the previously mentioned instance. The 

 weather was perfectly calm and fine. The carriages had been previously in 

 use throughout the day on the Grand Junction line, and the experiments 

 made with them will be hereafter noticed. It is sufficient to observe, that the 

 friction of these carriages would be reduced to its minimum by the work 

 they had undergone. 



The time of descent from to 22 post was •t'" 34=-25. As a check upon 

 the results, an experiment made with the very same carriages, performed on 

 the 8th July, and recorded in Table No. 6, may be referred to. In that in- 



