LOCOMOTIVE ENGINE. 
419 
Gauges.—L L, (Plates XC. and XCII.,) is a glass gauge for show- fig. 8. 
ing the height of the water in the boiler ; it is shewn detached in 
fig. 8, which is a section through the centre of it to a scale of Sc 
inches to a foot, or three times the size of the engraving. The 
gauge consists of a strong glass tube, A, fig. 8, about three quarters 
of an inch diameter outside, fitted into a brass socket, B B, at top 
and bottom, the joints being made steam-tight by hemp packing, 
put round the glass, and compressed against it by the glands C C, 
which are screwed in round the glass. From each of the socket- 
pieces B, a tube, D, proceeds with a cock in it and a screw on 
the end for fixing it into the fire-box ; and the piece E, containing 
another cock, is screwed into the lower piece, and the plug F into 
the upper piece, affording the means of putting the glass tube down 
into its place. When the two cocks in D D are opened, the water 
of the boiler rises in the glass tube to the same height that it is in 
the boiler, the upper part of the glass being filled with steam, 
the height of the water in it shewing always the level of the 
water in the boiler ; the cocks are for the purpose of stopping 
the communication, when required, from the gauge being out 
of order or otherwise. The cock in the piece D is for the purpose of clearing 
out the gauge, by allowing a stream of water to run through it ; and it is often 
necessary to open it when examining the gauge, in order to get rid of the bubbles 
of steam formed by the rapid ebullition of the water, which sometimes render it 
difficult to ascertain the precise height of the water. The difficulty is also in 
creased by the motion of the engine producing oscillation in the water ; but the 
disturbing effect is much diminished by choking the tube, or making the communica 
tion with the boiler through the tube D very small, so as to impede the motion of 
the water in the tubes. A small plug, G, is screwed in opposite each tube, B, to 
afford the means of clearing out the tubes D, by passing a wire through them when 
the plugs G are taken out. 
To afford an additional means of ascertaining the height of the water in the 
boiler, two gauge cocks, M M, are fixed in the side of the fire-box, one being four 
inches above the other, and the lower one, one inch above the top of the internal 
firebox. The boiler is generally filled at starting, until the water runs out at the 
upper cock ; and during working the water level is kept between the two cocks, 
and often up to the upper one. The cocks are opened occasionally to try the level, 
and if steam should ever be found to blow out at the lower cock, showing that there 
is not more than one inch of water over the roof of the internal fire-box, instant 
attention has to be paid to the feed-pumps, and the fire damped if necessary, to