model a screw clamp was arranged to secure the 

 guide wheels in position as set. This was done in the 

 case I have referred to when running in an irregular 

 circle; the steam valves were revolving stop-cock plugs 

 driven by bevel gearing from the crank shaft. The 

 throttle valve was an ordinary brass stop-cock, no 

 water feed pump; a funnel and stop-cock on top of 

 the boiler to fill it, a stop-cock in the bottom to 

 empty it. 



The boiler was first filled with hot water to heat it, 

 this was then drawn off and it was again filled with 

 boiling water to a taper screw plug representing a 

 gauge cock. To generate the steam a highly heated 

 round iron rod, nearly filling the copper flue, was 

 thrust into it . . . . 



I have referred to having seen the "Arabian," on its 

 first trial. The intimacy with Davis had been kept 

 up from the time of his first visit to Philadelphia, 

 and before he commenced building the "Arabian" 

 he showed me his drawings. I chanced to be passing 

 through Baltimore and stopped over to see Mr. Davis, 

 and found him at the shops steaming up the 

 "Arabian" for its first trial on the road, and I then 

 rode with him on its open platform, for it was before 

 the day cf cabs. He spent the evening with me in 

 Baltimore, and I have a very distinct recollection 

 of many of the reasons he gave for having adopted 

 the style of engine. 



In the first place he had a light strap railroad to deal 

 with, with many short curves; he must have weight 

 to give adhesion; he must turn the curves without 

 danger of running off, and with the least possible 

 friction; to accomplish this the bearing on the road 

 must be short; three-foot wheels, close together, met 

 this; to carry the weight central, the upright boiler 

 became a necessity. Trucks, if they had been con- 

 ceived cf, had not been successfully tried within his 

 knowledge. Six tons at that time was the utmost 

 admissible weight on four driving wheels; he was 

 more than doubling this, and was afraid to take 

 direct hold cf the driving axle by crank; that no 

 counterbalancing could prevent injurious hammering 

 on the light rails. He believed this was greatly 

 neutralized by the independent crank-shaft; the 

 strain being within the machine, he did not think 

 it would be injuriously transmitted through the 

 cog-wheels. He considered the independent crank- 

 shaft much safer than a carrying axle cranked: the 

 outside connection cf one pair of wheels to the other 

 could be counterbalanced. 



He did not calculate on fast running. That he said 

 was further along. The problem he had to solve 

 was an effective engine on light rails and short 

 curves; the time would come when both these would 

 be remedied. He certainly did produce the first 

 effective engine on the Baltimore and Ohio Railroad, 

 more than answering his own expectations. It for 

 years drew the passenger trains on both the main 

 road and the Washington branch, and was the model 

 from which many others were built, and successfully 

 lifted the company out of a state of great depression. 



No one can overestimate the value of the preserva- 

 tion of early efforts in all branches of mechanical and 

 civil engineering, relics, as landmarks in progress. 

 I cannot better close this paper than by a quotation 

 from a letter recently received from a well-known 

 engineer, W. W. Evans, on the subject of preservation 

 of models; he says: "No one knows the value of 

 models of useful inventions until many years after 

 they are made. John Stevens' first screw propeller, 

 with its engine and boiler as it stands in the Stevens 

 Institute, at Hoboken, 242 is to me a most interesting 

 and invaluable model, and so would be the little loco- 

 motive made by Peter Cooper, if it had been pre- 

 served, as I understand that it actually did more when 

 tried in proportion to weight and dimensions than did 

 the celebrated 'Rocket' of Stephenson, which engine, 

 now standing in the Patent Office in England, 243 I go 

 to see everytime I go to England, and also to see 

 another engine standing by it called 'Puffing Billy,' 

 which engine preceded the 'Rocket,' in time, eight- 

 een years. I take people to see it so they can judge of 

 the improvements we have made in seventy-three 

 years, as 'Puffing Billy' was built in 1812. Its axles 

 have square ends, and the driving wheels are fastened 

 on with wooden wedges; the frame is made of wood, 

 and it is trued up only at such spots where an attach- 

 ment was to be made; it is a 'rummey' looking affair, 

 but it is very interesting to see it and then turn to the 

 very splendid machines of the present day." [63I 



I have heard Mr. B. H. Latrobe say that the 

 "Arabian" never met with but one serious accident, 

 and that caused the death of its designer and construc- 

 tor. It was but a few days after our last evening to- 

 gether that the sad accident occurred. Mr. Davis 

 was treating the workmen of the Mount Clare shops, 



2« Now in the U.S. National Museum. 

 243 Now in the Science Museum, London. 



184 



