MECHANICS AND USEFUL ARTS. 39 



this amount of torsion, a power equal to 181 cwt. had to be applied to the 

 circumference of the wheel. With axles of five inches diameter, the angle 

 of torsion corresponding- to one inch deflection of the index, was found to 

 be 21 minutes, which required a power of 44 cwt. applied on the circumfer- 

 ence of the wheels of 30! inches diameter. 



Experiments have been made with cars running on six and four wheels, and 

 the results were collected in tables giving the number of miles travelled over 

 by the cars, the weight of the cars with their respective loads, and the largest 

 deflection of the indexes of both the apparatuses for flection and for torsion. 



With axles of 3! inch diameter, made of cast steel, and running under cars 

 with four wheels, and with a weight of 117*6 cwt. on each axle, the largest 

 deflection of the index by flection was 3 1-16 inch, which is equal to a side- 

 draught of 72 cwt. The tension of the extreme fibres of the axle in this 

 case is equal to 252 cwt. per square inch, and the deflection of the wheel 

 from its normal position is equal to 0'287 inches. The average deflection of 

 the index, with covered cars running on four wheels, however, was found 

 to be from 2| to 2| inches, requiring a side-draught of from 54 5-6 to 62f cwt. 



The largest deflection of the apparatus for torsion, in the same case, was 

 found to be 1 7-12 inches, which is equal to a power of 29 11-16 cwt. on the 

 circumference of the wheel, producing a tension of the extreme fibres equal 

 to 52 cwt. per square inch. The average deflection in this case was 1 1-12 

 inches, which is equal to a power of 20^ cwt. on the circumference of the 

 wheels. 



If the tAvo largest forces on flection and torsion act simultaneously, the ex- 

 treme fibres of the axle sustain a power equal to the square root of 352- + 52-, 

 which leaves 257 cwt. per square inch. This shows that the torsion increases 

 but very slightly the tension of the extreme fibres produced by the flection 

 of the axles. 



Such a power would be amply sufficient to produce a considerable bend 

 with wrought-iron axles, where the limit of elastic-it} 7 is approached by a 

 tension of the extreme fibres equal to 180 cwt. to the square inch. 



With axles of five inches diameter, and a load of 153'15 cwt. per axle, the 

 largest deflection produced by flection was 1 15-32 inches, which is equal to a 

 deflection of the circumference of the wheel from its normal position of 9-64 

 inches, and which requires a side-draught of 102 35-64 cwt. The tension of 

 the extreme fibres in this case is equal to 156 cwt. per square inch. 



The largest torsion was produced with a load of 164-25 cwt. per axle. The 

 deflection of the index was equal to 1-16 inch, which requires a power of 46i 

 cwt. on the circumference of the wheel, and the tension of the extreme fibres 

 is equal to 35 cwt. per square inch. 



If an axle is calculated to run 200,000 miles, and the largest deflection takes 

 place once in every ten miles, it (the axle) will break if it cannot be bent 

 20,000 times to this deflection from its normal position. In order to ascertain, 

 therefore, the largest load which an axle it able to carry with safety, it is 

 necessary to ascertain how far, and how often, the axle can be bent. 



Careful experiments made in this respect show that the maximum load of 

 a five-inch wrought-iron axle ought not to exceed 155 cwt.; that of a 4i-inch 

 axle, 113 cwt.; that of a 4-inch axle, 79 cwt.; and that of a 3f-inch axle, 

 70 cwt. 





 SUGGESTIONS RESPECTING KAIL WAY SUPERSTRUCTURE. 



The following excellent remarks on railroad construction, by John C. Traut- 

 wine, C. E. of Philadelphia, are from the Journal of the Franklin Institute: 



