ON RAILWAY CONSTANTS. 219 



In the third column F expresses a favourable wind, A an adverse wind, C 

 nearly calm, CC a dead calm, and S a side wind. 



The last experiment with a train of eight coaches, weighing nearly forty 

 tons, shows that, in a dead calm, the resistance of that train at $\\ miles an 

 hour amounted to the eighty-ninth part of its weight ; whereas the common 

 estimate of the resistance of such a train at that speed has been hitherto about 

 the 250th part of its weight ! This fact alone, were it unconnected with any 

 others, would sufficiently illustrate the enormous extent of error which has 

 prevailed hitherto in such estimations in railway practice. The third expe- 

 riment with eight carriages was made with a side wind, the effect of which is 

 abundantly manifested by the speed expressed in the last column. While 

 the same train, moving with a fair wind down the Madeley plane, had a re- 

 sistance equal to the 177th of its weight, at 26 miles an hour, its resistance 

 with a side wind was of greater amount at 17"7 miles an hour. The relative 

 effects of a fair and adverse wind are likewise exhibited in the third and 

 fourth experiments with six coaches, down the Whiston plane. The velocity, 

 which gives a resistance equal to the 96th part of the load, was 34^ miles an 

 hour with a fair wind, and only 27J with an adverse wind. 



It is evident, from these experiments, that the manner in which the atmo- 

 sphere resists a railway train, whatever it be, depends on the number of 

 coaches forming the train, and that the foremost coaches do not, by clearing 

 a passage for those which succeed them, produce any diminution of the total 

 resistance, which is worthy of attention in practical operations. 



The writer of this Report pointed out long since a probable source of re- 

 sistance, which the results above stated entitle to some attention. 



The wheels of the several carriages produce vortices of air around them, 

 and play in some measure the part of fanners or blowers. A considerable 

 force must be absorbed by so great a number of these wheels moving at 

 such a velocity. In a train of eight carriages we have thirty-two three-feet 

 wheels playing these parts of blowers, and revolving from four to five times 

 in a second. How much force must be expended in maintaining such a 

 motion, it is needless to say. But, besides this, another circumstance was 

 observed. In these experiments, as well as in general railway practice, it is 

 found that an extensive current of air moves beside a train, the current di- 

 minishing in velocity as the distance from the train increases. Immediately 

 contiguous to the side of the coaches the air moves with little less velocity 

 than the coaches themselves. Outside that is another current, moving at a 

 less rate, and beyond that another at a further diminished rate. There is 

 thus a succession of currents, one outside another, exending to a consider- 

 able distance at each side of the train. All the resistance produced by the 

 lateral friction of each of these currents upon each other must be brought 

 to the account of the aggregate resistance to the moving power ; and it is 

 evident that these resistances will depend on the length of the train and the 

 bulk of the coaches which form it. 



The following are the details of other experiments made on various gra- 

 dients, with a view of illustrating the same practical principles. 



