RACK RAILWAYS. 89 



this colony, the agent of the Abt Company states that the 1 in 10 

 at first contemplated, must if possible, be reduced to 1 in 12 J at 

 least, as this is the limiting grade in practice, up which an ordinary 

 adhesion locomotive could travel light with its own weight only, 

 in all weathers, so that any steeper grade would isolate the systems 

 connected by the rack line, as regards free circulation of ordinary 

 locomotive stock, and also much more expensive brake power must 

 be applied, as the ordinary adhesion brakes would be of little or 

 no assistance. Further, in the extremely steep rack lines which 

 form part of a general system to be worked by combined rack and 

 adhesion locomotives, the difficulty would occur of arranging the 

 boiler to suit both. The tilt in the barrel suitable to an excessive 

 grade, such as that allowable in a purely rack line of great steep- 

 ness, would be unworkable on the level or ordinary adhesion grades. 



Again, on the other hand, the usefulness of the system diminishes 

 considerably when the grades can be eased to 1 in 25 or there- 

 abouts, the gain not being worth the complication of a special 

 system, the exact limit depending upon the circumstances of each 

 particular case. 



The difficulty of the entry of the engine easily on to the rack 

 portion has been ingeniously got rid of by a contrivance invented 

 by Mr. Abt. The rack bars are continued for a short distance 

 on to the level or easy grade, at either end, and the last length of 

 them is bevelled off, as regards its depth, down to nothing, at the 

 end next to the adhesion line, and hinged vertically at the other 

 end to the previous rack bars. These end bars are supported 

 below by several strong spiral springs. The pinions on the engine 

 which are left free to revolve on the approach to the rack, are 

 thus gradually and easily, by means of the bevel and the elastic 

 movement of the end rack bars, engaged with it, and by the time 

 that the incline is reached, the pinions are in workable position 

 to be acted upon by the cylinders driving them. 



The changes between varying rates of grades on the rack must 

 be gradually effected in vertical curves — 4,000 ft. is the minimum 

 radius of these on the Nilgiri line, and 3,300 ft. is that recommended 



