502 INVENTION OF THE STEAM-BLAST. APPENDIX. 



1814, before the steam-blast was introduced by my father into 

 the chimney, and it was uniformly employed in every subse- 

 quent engine that was built ; but the orifice of the blast-pipe 

 was, I believe, in no instance contracted so as to give a less 

 area than that of the steam-ports. 



" The Stockton and Darlington Kailway was opened in 1825, 

 but as I was absent from England at the time, I cannot state 

 whether the engines constructed in Forth-street or at the 

 factory, for that line, had contracted blast-pipes or not. Shortly 

 after my return from America, I was frequently in the habit, as 

 a matter of business, of visiting the line alluded to, the super- 

 intendence of the locomotive engines being then under Timothy 

 Hackworth, with whom I was constantly in the habit of discussing 

 the remarkable effects produced by the blast in the chimney. It 

 was about that time, I believe, Mr. Hackworth had found that an 

 increased effect was obtained by contracting the orifice of the 

 blast-pipe. Considerable doubt was, however, then entertained 

 whether such contraction would be attended with any actual 

 economy in the working of the engine, for, although the com- 

 bustion was a little more excited, and a more copious amount of 

 steam was generated, it was believed that the negative pressure 

 produced on the piston counterbalanced in a great measure the 

 advantages mentioned. 



" During the construction of the 'Socket ' a series of expe- 

 riments was made with blast-pipes of different diameters, and 

 their efficiency was tested by the amount of vacuum that was 

 formed in the smoke-box. The degree of rarefaction was 

 determined by a glass tube fixed to the bottom of the smoke-box 

 and descending into a bucket of water, the tube being open at 

 both ends. As the rarefaction took place the water would of 

 course rise in the tube, and the height to which it rose above 

 the surface of the water in the bucket was made the measure of 

 the amount of rarefaction. 



" These experiments certainly showed that a considerable 

 increase of draught was obtained by contracting the orifice, and 

 accordingly the two blast-pipes in the ' Rocket ' were contracted 

 slightly below the area of the steam ports, and before she left 

 the factory the water rose in the glass tube three inches above 

 the water in the bucket. 



" I was quite aware at the time that Mr. Hackworth's 

 * Sanspareil ' was being constructed in the same manner, with 



