ON RAILWAY CONSTANTS. 



257 



deem it unnecessary to draw therefrom any numerical deductions with refer- 

 ence to the value of resistance. A comparison of the last trial of the train 

 of eight carriages with the first three trials of the same train is well worthy 

 of notice, as illustrating the powerful effects of a side wind. In the first case 

 the mean initial velocity at the top was 24 miles per houi-, and the mean final 

 velocity at the foot, 25"4 miles per hour. Under the influence of a side wind, 

 the initial velocity being 20*07 miles per hour, the final velocity at the foot 

 M'as only 17*69 miles per hour, with the probability of a further retardation 

 had the incline been longer. 



The following Table presents a summary of the calculations we have made 

 of the various amounts of resistance opposed to the different trains, on the lo- 

 calities and under the circumstances assigned. 



One of the important questions which the examination of such a series would 

 suggest is, whether any relation can be traced between the speed and the ex- 

 cess of resistance produced by the speed, and to what extent this excess is mo- 

 dified by altering the size of the train. To enable the reader more readily to 

 perceive what degree of connection subsists, the following table is constructed, 

 presenting, in one column, the speed in miles per hour ; in anothei", the weight 

 and description of the train ; and in a third, the excess of resistance in pounds 

 per ton, or difference between' the total resistance and the resistance due to 

 friction alone, the whole being arranged in the order of increasing speed, group- 

 ing together experiments with trains of unequal sizes when their respective 

 velocities were found nearly equal. 



The excess of resistance, as exhibited in the fourth column, evidently in- 

 creases with the speed. Thus, at 20*54 miles, the excess is 3*31 lbs.; at 25-86 

 miles, 4*25 lbs ; at 29*61 miles, 6*65 lbs. per ton, in a train of eight carriages. 



1841. 



