commences to close b, and at a predetermined pressure, obtained by adjusting the screw d, it closes b entirely, which only commences to open again as pressure falls. When no constantly burning pilot light is used, there is a small groove cut in the opening b, so that a never completely closes it, and enough vapour is admitted to keep the main burner just alight. In some cars no automatic regulator is used, the fire being controlled entirely by the driver from the seat. It should be understood that although the automatic regulator prevents vapour passing to the burner when a maximum predetermined pressure of steam in the boiler is reached, there is always a tap in reach of the driver which enables him to turn off the supply of fuel at any time.
Paraffin Burners.—For burning paraffin instead of petrol, burners of a somewhat different description are employed, as paraffin requires more heat to vaporise it sufficiently, and when vaporised a larger supply of air is necessary for complete combustion. If these conditions are not obtained, a paraffin burner will smoke and give off insufficient heat. Clarkson's paraffin burner is shown (figs. 5 and 5a). In this the paraffin is forced by air pressure through the vaporiser, which takes the form of a coiled pipe above the flame of the burner. It then passes through the vapour pipe to the jet nozzle, and air is admitted by the door of the mouthpiece, and mixes with the paraffin vapour, which rushes along the inducing-tube and issues from the circular opening below the cap, where it ignites so that a spreading ring of flame is formed, which jets out all round the coiled ring of nickel wire shown in the figure; this and the shape of the circular trough tend to spread the flame, so that it completely covers the bottom of the boiler. The intensity of the fire is regulated by a control lever connected to a handle by the side of the seat, and it will be seen by examining the connections at the bottom of fig. 5 that the needle which increases or decreases the size of the hole of the jet nozzle. by which the vapour enters from the vapour-pipe into the inducing-tube, also proportionately raises or lowers the cap, so that the
