PaOCEEniNGS OF THE POLYTECHNIC ASSOCIATION. 868 



This rail is also set iu brackets, fitting on either side and setting 

 underneath, the branches of the base setting upon the brackets by 

 such angles of their lower edges as to make the whole structure self- 

 binding or self-locking. As in the case of* the T rail, the joints are 

 regularly distributed throughout the structure, the brackets forming 

 a continuous bridge from tie to tie, and no one tie being allowed to 

 have more than one joint. 



A prominent and favorable feature of this form of rail is the per- 

 pendicular depth given to the brackets, yielding corresponding 

 bracing and supporting strength of base and sides. 



The rail is literally a combination tripple rail ; its strength and 

 security being greater than that of any other form with a given qual- 

 ity and quantity of materials. 



In this case, also, the brackets are secured to the ties by means of 

 stout knees or dogs made of wrought or cast iron, their faces being placed 

 at an obtuse angle to correspond with that formed by the face of the 

 tie and the side of the bracket. The holes in the dog's beino^ made 

 oblong in the line of their bearing, admits of keeping them close upon 

 the brackets without withdrawing the bolt screws, which are the 

 same as those used in the case of the T rail, being put to the work in 

 the same manner and with the same facihty. 



In this arrangement, also, we dispense with small plates, chairs and 

 fish bars ; simply forming continuous lines of rails and brackets, and 

 avoid the necessity of special fitting at local points, rails and 

 brackets alternately overlapping each the other's joints. 



In prosecuting this system of construction, the ties being set, the 

 rails and brackets laid in line of position, the process of placing the 

 dogs or knees, and of setting the screws and turning them to their 

 place, becomes simple and straightforward work. 



The grand advantage of the cone and arch form of rail will be 

 found in the latitude afforded for variety and choice of mate- 

 rial for construction, while the side brackets must, as a matter of 

 course, be made of steel or wrought iron ; the central rail may be 

 wrought of any material which under tke conditions may possibly 

 answer the purpose, the margin being bounded by steel, wrought iron, 

 simple cast iron, and cast chilled iron. 



This form of rail has also the advantage of brmging all the metal 

 where it is most needed to give the utmost strength for long con- 

 tinued wear. In fact, it is that form which, the more it is worn bj 

 use, the better it may become, provided the metal be good and rea- 



