466 REPORT — 1891. 



creases the security against fracture of an individual tooth ; 

 and, even if this should arise, from any exceptional cause, it 

 would not be followed by any serious consequences. 



The component bars of the Abt rack are laid with broken 

 joints, and in this way the rack-rail becomes practically one 

 continuous structure, there always being one or more whole 

 bars at the point of junction between the ends of any two 

 lengths in one line of bars. Moreover, the breaking of joint in 

 the rack allows of equalising throughout the length the in- 

 fluences of expansion and contraction through variations of 

 temperature. These racks are secured to chairs which keep 

 them in a fixed position, but allow of any individual bar being 

 taken out and replaced in a few minutes. 



The pinions of the engine are constructed with as many 

 separate discs as there are separate rack-bars, each disc cor- 

 responding to one line of these. They are provided with teeth 

 corresponding to the pitch of the racks, and they are stepped 

 in relation to the teeth in each to correspond with the broken 

 pitch of those in the rack. These pinion-discs are in elastic 

 contact with the shaft actuating them. This is obtained by 

 means of springs, through which each of these discs obtains a 

 small relative motion to each other, allowing of any slight ad- 

 justment in case of irregularity of pitch in the teeth of the 

 rack-rails, thus producing a perfectly automatic contact of the 

 teeth. Curves of any radius within the limits of application 

 to railway-construction can be laid with the rack. The same 

 bars are used on the straight as on the curved line. The 

 auxiliary power is in the form of pinions driven by separate 

 cylinders worked independently of those moving the ordinary 

 adhesion driving-wheels with which the engines are fitted ; so 

 that, whatever the condition of the road may be, or however 

 much the adhesion wheels may slip from climatic changes, 

 the pinions work steadily on, and raise the load by means of 

 the fixed racks. This is one of the important features of this 

 system : as the pinions are working in the rack, thus the motive- 

 force becomes a given power working against a fixed resistance, 

 and is in no way influenced by the condition of the atmosphere, 

 as is the case with the ordinary engines, in which the adhesion 

 varies according to the state of the rails. 



Eack-rail locomotives can be built of specially large tractive 

 power by coupling two or more driving-pinions one behind the 

 other ; and experience shows that, by placing one of these 

 coupled pinions a little in advance in reference to the time of 

 contact with the teeth of the rack, coupling heightens the uni- 

 formity and smoothness of motion. 



One of the most ingenious features of the Abt system is the 

 arrangement by which the engine-pinions enter or leave the 

 rack sections of line without entailing any stoppage of the train. 



