The diagrams from the Great Eastern engines were, on the whole, the best which were taken by us. On one of these trips I was able to get the accompanying most interesting pair of diagrams, which were published by me in the appendix to my treatise on the Indicator. One of them was taken at the speed of 50 revolutions per minute, and the other at the speed of 260 revolutions per minute, running in the same notch with wide-open throttle. The steam pressure was higher at the rapid speed. They afford many subjects of study, and show the perfect action of the indicator as at first turned out, at this great speed. I learned afterwards that the almost entire freedom from vibration at the most rapid speed was due to the gradual manner in which the pressure fell from the beginning of the stroke. This fall of pressure before the cut-off I fancy was caused largely by a small steam-pipe. Our last diagrams were taken from a locomotive on the London and Northwestern, by the same four operators as on the Great Eastern trips. We ran from London to Manchester. On our return trip Mr. Webb joined us at Crewe, and accompanied us to London. I am sorry to say that in one respect the revelation of the indicator here was almost inconceivably bad. Mr. Ramsbottom did not protect his cylinders, but painted these and the steam-chests black, and in this condition sent them rushing through the moist air of England. If the steam cooled by “Mr. Beattie’s refrigerators” was wet, that in Mr. Ramsbottom’s cylinders seemed to be all water. A jet of hot water was always sent up from each of the holes in the cover of the spring case to a height of between one and two feet. We had much trouble to protect ourselves from it, and it nearly always drenched the diagram. I never saw this phenomenon before or since. I have seen the steam blow from the indicator cocks white with water when the indicators were removed. But I never saw water spurt through the spring-case cover, except in this instance. Truly, we said to each other, Mr. Ramsbottom has abundant use for his trough and scoop to keep water in his tanks. It was on this trip that I observed how enormously the motion of a black surface increased the power of the surrounding air to abstract heat from it. While we were running at speed I many times laid my hand on the smoke-box door without experiencing any sensation of warmth. I wondered at this, for I knew that a torrent of fire issuing from the tubes was impinging against the opposite surface of this quarter-inch iron plate. In approaching Rugby Junction I observed that the speed had not slackened very much when I could not touch this door, and when we stopped, although the draft had mostly ceased, I could not come near it for the heat. At the full velocity with which the air blew against this door the capacity of the air to absorb heat evidently exceeded the conducting power of the metal. [Illustration: W. H. MAW] CHAPTER IX