486 ROBERT STEPHENSON'S NARRATIVE. APPENDIX. 



criterion of what the adhesion would be on an edge-rail, my 

 father felt sure that there was no essential difference between 

 the one and the other. 



" The construction of my father's first engine was very much 

 after the same plan as that made by Mr. Blenkinsop ; but the 

 combined power of the two cylinders was communicated to the 

 wheels which supported the engine on the rail instead of to 

 the cog-wheel, which, in Mr. Blenkinsop's engine, acted on 

 a cogged-rail independently of the four supporting wheels. 

 This engine was completed and tried upon the Killingworth 

 railway on the 25th July, 1814. It performed its duties with 

 comparative success; but, having to compete with horses, was 

 considered barely economical. At the end of the year, how- 

 ever, the steam-power and horse-power were found to be very 

 nearly on a par with each other in regard to cost. A few 

 months of experience and careful observation upon the opera- 

 tion of this engine convinced my father that the complication 

 arising out of the action of the two cylinders being combined 

 by spur-wheels would prevent their coming into practical appli- 

 cation. He then directed his attention to an entire change in 

 the construction and mechanical arrangements, and in the fol- 

 lowing year took out a patent, dated February 28th, 1815, for 

 an engine which combined in a remarkable degree the essential 

 requisites of an economical locomotive that is to say, few 

 parts, simplicity in their action, and great simplicity in the 

 mode by which the power was communicated to the wheels sup- 

 porting the engine. 



" This second engine consisted as before of two vertical cylin- 

 ders, which communicated directly with each pair of the four 

 wheels that supported the engine by a cross-head and a pair of 

 connecting rods ; but in attempting to establish a direct com- 

 munication between the cylinders and the wheels that rolled 

 upon the rails, considerable .difficulties presented themselves. 

 The ordinary joints could not be employed to unite the engine, 

 which was a rigid mass, with the wheels rolling upon the irre- 

 gular surface of the rails ; for it was evident that the two rails 

 of the line of railway could not always be maintained at the 

 same level with respect to each other that one wheel at the 

 end of the axle might be depressed into a part of the line which 

 had subsided, whilst the other would be elevated. In such a 

 position of the axle and wheels it was clear that a rigid com- 

 munication between the cross-head and the wheels was im- 



