Award of Medals, ^-c, at Kilburn. 
753 
For the drawings of the engine I am indebted to Mr. Maw, the 
editor of ' Engineering,' who has kindlv lent the Society 
the electro ; whilst for that of the valve gear I am indebted to 
the editor of the ' Engineer ' for a similar drawing to that which 
appeared in the issue of June 20th (Figs. 45 and 46). 
Fig. 46. — Vahe-gear of TredthicVg Steam-engine. 
16- > 
By way of explanation it may be stated, that the cylinder is placed in the 
boiler, and is thus surrounded by a powerful steam-jacket, which is of great 
importance, as it is open at the top, and the cold air, which must of necessity 
enter with the piston in its downward descent, would otherwise cause con- 
siderable condensation. The piston was worked entirely by steam admitted 
below, forcing it up, whilst its descent was due to the balance-weight 
attached to an enormous fly-wheel. Instead of a slide-valve for the admission 
and emission of the steam, Trevithick used a two-way cock in a three-way 
shelL The cock is kept tight by a bent spring, the action of the spring being 
adjustable by means of vice-screws. This is shown in the second figure. 
The lever of the cock is acted on by a long crooked spring bolted to the 
framing, and this spring keeps a bowl 5 inches, in diameter continually pressed 
against a cam-plate fixed on the crank-shaft. ITie necessary action on the 
steam-cock is brought about by the influence of the cam on the bowl acting 
on the spring, and the only way of stopping the engine consists in putting a 
wooden wedge or scotch between the bowl-lever and a piece of iron screwed 
to the frame for that purpose. This scotch must be sUpped in when the 
exhaust-port is open and the steam-port closed. The bowl is thus prevented 
from following the cam, and the engine is stopped. The only way to regulate 
the speed is by altering the pressure of steam, and the slight adjustment of 
VOL. XV. — S. 8. 3 E 
