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Murdoch's Little "Steam Devils"
(Illustration : replica of Model No1 held at Murdoch
House)
Model No3 - 1791
(Piston Diameter-1", Stroke-1 & 1/2" - Slide valves & Double
Acting)
Towards the end of 1786, William Murdoch's work on his first two model-steam
carraiges had become interrupted due to business and family matters. By
then it was also clear that James Watt had no intention of helping William
in his quest for steam-locomotion.
A full five years lapsed before William took interest in his steam-carraiges
again. There is one reference that by the summer of 1791 William had built
another model carraige with a more sophisticated power unit. The reference
comes in a letter from William's son John, to James Watt Jr.
DOCUMENTED EVIDENCE :
 1815,
May - John Murdoch (William's son), writing to James Watt Jnr
In a postscript to the letter
"The model of the steam engine with one inch cylinder that works
double with slide valves was made in August 1791, and it is now at the
foundry"
AUTHORS COMMENT :
This reference of Model No3 quite often confuses it with the models
from 1786 because of it's one inch piston, something which also confused
Boulton Jr who stated to Watt Jr that he had seen it working in 1784 at
Redruth. (Although he was mistaken, it does confirm the earlier existence
of a onch inch model chariot.)
It is unclear if the "foundry" John refers to is the Soho Manufactory
in Birmingham, or Budge's Tucker Mill Foundry in Cornwall. It is thought
to be the latter.
"Old Budge" had previously tried to aquire William's services when his
original 5 year tenure to Watt had expired. Watt's conditional "offer"
of 1784 put paid to that, but it seems that by 1791 the disinterest and
indifference of Boulton and Watt had rekindled the proposed partnership
between Murdoch and Budge.
William Murdoch's work on this particular steam carraige was free of
the "conditions" laid out by James Watt in 1784, any terms of any agreements
long since lapsed, so he was free to do as he wished.
Although it is but a single referrence, it is quite possible that Model
No3 was a larger scale model built to test idea's and methods for a full
scale carraige.
What became of the third model is unknown, but it is unlikely if it
ever survived.
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