Editing Newcomen atmospheric engine (section)

===Automation {{anchor|Humphrey Potter}}===
[[File:Humphrey Potter.png|thumb|Humphry Potter tying his strings.]]
In early versions, the [[valve]]s or ''plugs'' as they were then called, were operated manually by the ''plug man'' but the repetitive action demanded precise timing, making automatic action desirable. This was obtained by means of a ''plug tree'' which was a beam suspended vertically alongside the cylinder from a small arch head by crossed chains, its function being to open and close the valves automatically when the beam reached certain positions, by means of tappets and [[escapement]] mechanisms using weights. On the 1712 engine, the water feed pump was attached to the bottom of the plug tree, but later engines had the pump outside suspended from a separate small arch-head. There is a common legend that in 1713 a ''cock boy'' named Humphrey Potter,<ref>{{Cite web|url=https://archive.org/details/steamenginefami00lardgoog/page/n71|title=The steam engine familiarly explained and illustrated; with an historical sketch of its ...|date=6 May 1851|via=Internet Archive}}</ref> whose duty it was to open and shut the valves of an engine he attended, made the engine self-acting by causing the beam itself to open and close the valves by suitable cords and catches<ref name=EB1911>{{EB1911 |wstitle=Steam Engine |volume=25 |pages=818–850 |first=James Alfred |last=Ewing |inline=1}}</ref> (known as the "potter cord");<ref>
{{cite web
 |url         = http://www.history.rochester.edu/steam/carnegie/ch7.html
 |title       = Chapter 7: Second Patent
 |publisher   = www.history.rochester.edu
 |access-date  = 6 July 2009
 |url-status     = dead
 |archive-url  = http://arquivo.pt/wayback/20090708035343/http://www.history.rochester.edu/steam/carnegie/ch7.html
 |archive-date = 8 July 2009
 |df          = dmy-all
}}
</ref> however the plug tree device (the first form of [[valve gear]]) was very likely established practice before 1715, and is clearly depicted in the earliest known images of Newcomen engines by [[Henry Beighton]] (1717)<ref>
{{cite web
|url=http://www.scienceandsociety.co.uk/results.asp?image=10280720&wwwflag=2&imagepos=4
|title=Science and Society Picture Library – Search
|publisher=www.scienceandsociety.co.uk
|access-date=6 July 2009}}</ref> (believed by Hulse to depict the 1714 Griff colliery engine) and by Thomas Barney (1719) (depicting the 1712 Dudley Castle engine). Because of the very heavy steam demands, the engine had to be periodically stopped and restarted, but even this process was automated by means of a buoy rising and falling in a vertical stand pipe fixed to the boiler. The buoy was attached to the ''scoggen'', a weighted lever that worked a stop blocking the water injection valve shut until more steam had been raised.