TRANSACTIONS OF SECTION J. 467 



This is a necessary feature, as these engines run over the or- 

 dinary road by means of their adhesion wheels, and only bring 

 into use the auxiliary power on the steep-grade sections. 



This entering-tongue is built up of a series of bars corre- 

 sponding to those in the rack, about 10ft. long, hinged at the 

 end which joins the continuous rack, and rests upon strong 

 springs, usually of the volute form. The teeth in the portion 

 at the hinged end are the same as in the permanent rack, but 

 are gradually diminished in height towards the outer end, by 

 planing the top of the teeth away in a taper form, giving the 

 tongue a wedge shape ; so that, when the pinion passes on to 

 the movable portion, the teeth of the pinion or pinions slide 

 into the increasing depth of teeth, the bar yielding until true 

 contact is obtained. This arrangement, as might be expected 

 from its simplicity, never fails in action, and the train enters 

 the rack section, at five or six miles an hour, without any ap- 

 parent blow or noise. The pinions are caused to revolve in the 

 direction the engine is travelling at a slow speed before the 

 entering-tongue is reached. 



On entering the rack sections the adhesion machinery con- 

 tinues to work as before ; the driver, having already started the 

 auxiliary engines, has only to adjust the regulator to meet the 

 required power. On leaving the rack sections steam is shut off 

 from the auxiliary cylinders, and the adhesion wheels once 

 more become the only motive-force employed. 



On these steep-grade sections the engine developes the full 

 power by adhesion and by the rack pinion ; there are therefore 

 four beats of the exhaust in place of the usual two, and this has 

 the effect of increasing the draught through the fire-grate, and 

 thereby increases the steam-raising power of the boilers at the 

 time when a large quantity of steam is required. The ordinary 

 engine going up a bank has its speed reduced by the increased 

 resistance, and, the blast from the exhaust being less frequent 

 than when running on low grades at a higher speed, the boiler 

 is less capable of maintaining the steam-pressure when it is 

 most required. 



The descent of long adhesion grades is a source of danger 

 in weather producing greasy rails, and to meet this condition 

 powerful brakes must control the descending train. The brake 

 arrangements on the Abt engines are most efficient, reducing 

 the danger of the descent of steep grades below that of descend- 

 ing on ordinary long adhesion grades. There are first the 

 ordinary steam-brakes on the adhesion driving-wheels of the 

 engine, and the vehicles are fitted with one of the continuous 

 brakes now largely used on most railway systems in Europe. 

 In addition, there are the brake-discs on the pinion-shaft, by 

 which the pinion can be completely locked, and the train held 

 stationary at will. 



