514 



MEMOIR OF DANIEL TREADWELL. 



IV. Curves, — One of the questions of considerable importance in the econonry of railroads which has 

 yet remained undetermined, is presented in the resistance produced by passing the loads over the curves 

 in the road, made in horizontal planes, as compared with moving in straight lines upon the same planes. 

 The Worcester road contains no level curve of sufficient length to 3'ield any experiments for solving this 

 question. I often made direct observations, however, upon the dynamometer, as the trains passed the 

 short level curves, and I was seldom able to perceive any sensible increase of the draft over that required 

 for the same train upon the straight parts of the road. 



A single experiment was tried on a part of the road three miles in length, and made up of a series of 

 curves. To find the resistance produced by the curve alone we may take the resistance due to the com- 

 mon friction on the level and straight railway as shown by these experiments, and the resistance due to 

 elevating the load as shown by calculation, and the sum, whatever it maj r be, which is required to 

 make them equal to the actual and observed resistance ma}' be taken as the resistance due to the curves. 

 The results from this experiment foiled to show any essential resistance from the curves hy the method 

 followed, and yet it is evident that the cars pass more freely upon the straight than upon the curved 

 pints of a railway. ... I think that we may conclude that the resistance from a curve of 2,000 ft. radius 

 is not greater than s^^th part of the load, or an elevation of two feet in a mile. With curves of a smaller 

 radius the resistance is increased probably in a much more rapid proportion than that of the reduction of 

 the radius. 



A more important objection to curves than that of their increasing the resistance, however, is found 

 in this : that as they generally pass round hills or through deep cuts, it is impossible for the engineer 

 when upon them to see whether the road is clear and passable for mam* rods before him. Hence he 

 must either run very slowly, or be in constant danger of accident. This danger is so great that it is 

 always advisable to obtain for all railways straight lines, if possible, even if at the disadvantage of hav- 

 ing them of such ascents as shall yield resistances many times greater than would be given by the curves 

 for which they have been substituted.* 



V. Experiments to determine the Resistance of Cars mounted upon Gudgeons of different Sizes, when 



running upon Railroads. 



Saturday, October 29th, run with the engine Meteor twice to Newton Corner, drawing each time two 



cars, as follows : 



Experiment Xo. 1. 1 car carrying apparatus and two persons; gudgeons 1| inches in diameter, weight, 4,670 lb. 



1 car loaded with iron; gudgeons 3 inches in diameter, weight 11,150 



15,820 lb. 

 Experiment No. 2. 1 car carrying apparatus as in experiment No. 1 (the same car and load was used 



for the apparatus in all the experiments), weight . . 4,670 1b. 



1 car loaded with stone and iron; gudgeons \\ inches in diameter, weight . . . 9,210 



13,880 lb. 



The wheels of all the cars used are three feet in diameter. The weights named are those of the cars 



1 their loads. 



© 



* The effect of curves contains many factors, — the relative height of the inner and outer rails, the form of the tread of the 

 wheels, the length of the train independent of the load, and the velocity. It is still a subject of discussion with civil engineers. 

 The practical objection to curves as regards safety is fully acknowledged, even when the road is worked with the aid of the 



J t _ 1 "% r ^T XT' ~T* *•».«« * 1 _ 



earn 



_ m Mr. N. ST. Forney, in his book on Locomotives, says (1886): "It may be stated that the most recent experiments 

 have shown that the resistance of good American cars does not exceed 6 lb. per ton of 2,000 lb. at very slow speed on a straight 

 and level track. With reference to the influence of speed on the resistance, it must be admitted that our knowledge is very in- 

 exact, and probably the law or laws which govern it is not well understood. Our knowledge of the resistance due to curves is 

 also in a very unsatisfactory condition, but the most reliable information we hare indicates that the resistance is equal to about 

 half a pound per ton of 2,000 lb. per degree of curvatm. ." Mr. Treadwell's experiments with a speed of 15 miles an hour, a 

 curve of 2,000 feet radius (3°) treated by the methods now adopted, would give a resistance of 8.5 lb. to the ton of 2,240 lb., 

 substantially the same as that obtained from recent exj rimejits. — W. 



