MECHANICS AND USEFUL AliTS. 55 



lines of narrow roads, this is the first to our knowledge on a 6 feet gauge, 

 and we doubt whether a train half a mile in length and weighing in toto 

 nearly or quite 1,800 tons has ever before been hauled over a road as crooked 

 as the Delaware River portion of the Erie by a single engine. The smallest 

 radii of curves on the whole line is 955 feet, and the greatest inclination 60 

 feet per mile. The most difficult points of course are those in which curves 

 and grades are combined for long distances or at frequent intervals, and the 

 equation of grades, curves and distances form some of the most perplexing 

 problems ever presented to the civil engineer. The smallest number of cars 

 hauled at any time was 22, and this was where a curve 1,294 feet long and 

 1,146 feet in radius was combined with the maximum grade of 60 feet per 

 mile. The engine, No. 210, which hauled 100 cars at a speed of 6, 8, or even 

 14 miles per hour on levels and up grades of 6 feet per mile, combined with 

 curves hi many instances, as also through curves of 955 feet radius on level 

 points on the Delaware, stuck fairly in the five-degree curve above mentioned, 

 but started again and went through after being pushed about half a rod by 

 another engine ; a fact indicating a very close balance between the power and 

 the resistance. 



Experiments on the resistance opposed to motion on railroads are yet very 

 indefinite, and any data from this experiment may be of some value. The 

 variable elements are so numerous and complex that probably no two experi- 

 ments have ever been made under precisely similar circumstances. Even 

 the wind exerts an influence which is difficult to compute, and it is not yet 

 agreed whether a head or a side wind is most objectionable, as the latter 

 blows out and continually replaces the air contained between the cars. The 

 speed has evidently a very great influence on the resistance of the air, and by 

 more rapidly consuming the steam affects very seriously the ability of the 

 engine to haul with great power. The absolute highest pressure in the 

 boiler of Xo. 210 with this train was 165 Ibs., or 150 above the atmosphere, 

 and probably the average pull on the couplings of the forward car, in the 

 tightest places, was about 15,500 Ibs., or equal to more than one third of the 

 whole weight on the driving-wheels. It is only by a liberal flow of sand 

 upon the rails that the wheels can be prevented from slipping under snch 

 circumstances, and it may be remarked that the wheels, when once slipping, 

 have a most discouraging property of polishing the track. The only safety 

 in a ve"ry severe pull is in a dry, gritty rail, well sprinkled with sharp sand. 

 The engine which was employed in this experiment is a most extraordinary 

 machine, and is perhaps only equaled by three others on the same road, 

 built from the same patterns. The design was by James B. Gregg, Esq., of 

 Susquehanna, and the whole weight is 66,000 Ibs., of which 4,000 Ibs. are 

 supported by the two pairs of driving-wheels, and 26,000 by the truck. It is 

 outside connected, the cylinders being 17 inches in diameter, with 24 inches 

 stroke of piston. The valves are worked by the link motion, and when mov- 

 ing very slowly the steam acts nearly at full pressure for 23|- niches of the 

 stroke. With no means of testing directly the actual pull on the train or 

 even of approximating it by finding the average pressure hi the cylinder when 

 working expansively on level portions, we despair of settling any vexed ques- 



