ON AMIMIICAN PERMANENT AV VV. 



605 



detiiils, or in the application of the principle. This form of switch 



nsist.3 simply of a movable pair of split or tapering rails, which aw; 



stoned to the two inside rails of the four that come together, the outer 



ils being hxed, and connected and made continuous with the single 



ack from which the divergence takes place. Those split rails at the 



posite end are free to bo shifted sideways and move with each other, 



ing tied together to a certain fixed distance apart by rods, this dis- 



nco being made so that only one of them can be in contact with a fixed 



nil at ihi\ same time, the other being separated from the fixed rail by a 



ace, calleii the * throwing ' of the switch, suflifient to pass the flanges 



wheels of trains. The free end of the pointed rails is called the 'toe,' 



a the fixed or pivot end the 'heel' of the switch. At the heel, the 



xed distance from the adjoining rail must be enough to pass wheels 



sily. Ifc is essei\tial that the point Avhen pressed up against the fixed 



r ' stock ' rail, as it is called, should leave no projocticn that awheel 



pproaching the switch cnnld run against. For some years it was 



ustomary to make the points quite blunt, and to cut a recess into the 



ido of the stock rail for the point to fit into ; but as now made, the 



oint rails are tapered down to a tliin wedge, and shaped .so as to fit 



ery closely to the stock rails resting on th'jm, and having the thin point 



Iso tapered for a short distance from the end, so that (here will be no 



isk of the wheels touching the point rails until they reach a thicker 



art. Nothing has to be done to the stock rails, and no changes of 



mpcrature or creeping of rails will aflect the point rails. The throw of 



le switch is usually made about 3^ or -l- inches, to avoid any danfjer 



f the open end of the point being struck by the back of a wheel, although 



ss throw would answer. Sometimes short guard rails are u.sed in 



tont of the points to protect them. Tiie two point rails require to l)e 



onnccted together by rods or bars, which should be as low to the sui'- 



ace of the cross-ties as possible, and rigid vertically, while flexible to 



lome extent sideways to allow of self-adjustment. 



Split switches are made by a number of firms, each of which usually 



las some special patent or detail of its own in tlu' style which it builds. 



"'ig. 1, Plate VIII., shows the splifc switch as made by the Pennsylvania 



keel Company, which will very well illustrate the type. The form of 



onnecting bar is also shown. The two arms of the liar ai-e rigidly 



ttached tu the webs of the rails, and are secured together in the centre 



ly means of two flat ])late.s, which lay on each side nf them, and are 



ivcted together through a separating block. The iiniis. having only onv 



ivet in each, can adjust themselves between the j)Iates about this rivet as 



pivot. The point rails of this Company are made 15 feet long, beinc;- 



nc-half of a ;]0.feet rail. They are planed and tapered down without 



)eing heated, and are shaped so as to com])letely fit (he stock rails and 



o rest on the flanges of the same throughout the whole length of thi- 



apcred portion, in such a manner that the point lails receive substantial 



uj.port if required, altliough the wheels do not conic in contact with them 



intil they have pas.eed the extreme end. The slide plates under the point 



Mils are of wrought iron, qnite plain e::cept near the point, where they 



!xtend also under the stock rails, and have the ends tinned up to hold rail 



)raees. 



When a train appi'oaclies a split svviteh by the heel, it is called ii 

 ' trailing switch ; ' but if the toe or point is approached first, then it is 

 called a ' facing switch.' Single point switches arc sometimes made, with 



