258 



REPORT — 1841. 



In like manner, the excess at 29*3 1 miles per hour is 7*2.5lbs., and at 33"58 

 miles, lO'^Slbs. per ton, in a train of six carriages. 



So in a train of four carriages, at 22*8 miles, the excess is 4*65 lbs.; at 34*88 

 miles, 9'181bs.; and at 37'34 miles, 13*46 lbs. per ton. 



In a train of three carriages, at 22*5 miles, the excess is 2*22 lbs. ; at 26*16 

 miles, 6*07 lbs.; and at 29*60 miles per hour, 10*26 lbs. per ton. 



The trains of four and eight carriages respectively, showed an excess of 

 about half a pound only, but their motion was in some degree affected by 

 the wind. 



The excess of resistance per unit of the load increases as the size of the 

 train diminishes, though not in the same proportion. This consequence would 

 naturally be expected from the circumstance of an equal frontage being ex- 

 posed to the air, whether the train consist, for instance, of three or eight car- 

 riages. Whatever resistance may be occasioned by the atmosphere acting on 

 that frontage would in the one case be divided over three, and in the other 

 over eight carriages. The fact of its not increasing in the same proportion 

 pi'oves that the train is subject to a resistance independent both of friction 

 and mere frontage, and that in fact many complicated causes conspire to pro- 

 duce the entire resistance. 



At the speed of 29 to 30 miles per hour there is a group of experiments 

 made with three, six and eight coaches, which seems best to exhibit the effect 

 alluded to. The increase of the train from three to six coaches, diminishes 

 the excess per ton about 3 lbs., and increases the total excess of resistance in 

 the proportion of 1 to 1^, not as 1 : 2, which is the proportion of the loads. 



We do not, however, consider the observations to be as yet sufficiently nu- 

 merous to warrant the foundation of any specific theory of resistance. The 

 number of experiments in each group is extremely limited ; some of the cir- 

 cumstances influencing the results, as for instance the wind, are not to be 

 estimated, and therefore we deem it wiser to abstain from entering into the 

 mathematical consideration of the laws which regulate the motion of solid 

 bodies through a fluid medium until we can procure a mean from a large col- 

 lection of groups of facts similar to those of which we have just afforded a 

 specimen, otherwise we shall be in danger of having our inferences over- 

 turned by succeeding experiments, and discredit thrown upon the character 

 pf our inquiries. 



