In setting up turn-tables it is necessary that the foundation at centre, upon which the pivot rests, should be of the most substantial character, so as not to be liable to settle. The circular track, which may be made of light rails, say 28 or 30 lbs. to the yard, should be level, and the table should be so adjusted as to swing clear of the circular track when loaded. The pit required is quite shallow near the edge and deepens towards the centre. Provision is made for covering the entire pit by a platform turning with the table, but this should be avoided whenever possible, as the best constructed cover does offer some resistance in turning. Even in roundhouses, where a covered pit might be considered preferable as presenting a smooth floor for crossing in any direction, it has been found advisable, in view of the greatest ease in turning and the facility offered by the open pit for cleaning, to dispense with the cover. The centre upon which the table turns is constructed of the best cast steel, and consists of conical rollers of steel between two steel plates grooved out to receive these rollers. This part of the table must be kept clean and well oiled, say with best sperm or lard oil and tallow of such a consistency as not to harden in cold weather. The top cap at centre is held in place by a circle of bolts. These bolts take the entire weight of the table and load; by slacking off the bolts the table can be lowered on the wheels on the circular track and the cap lifted off to gain access to the plates and rollers. These should be opened, examined and cleaned at least once every three months. Under the cap and between it and the top of the centre box are segments of wood. These can be altered in thickness to bring the table in proper adjustment. If the centre foundation settles, these segments should be thinned sufficiently to enable the table to be screwed up to a proper height. With proper care such tables are practically indestructible.[105] [105] Wm. Sellers & Co. QUESTION 454. _Is there any other method of turning locomotives?_ _Answer._ Yes; what is called a ~Y~ is sometimes used. This consists of a system of tracks laid somewhat in the form of the letter ~Y~, as shown in fig. 229, in which _A B_ is the main track, with two curves, _A C_ and _B C_, laid as shown. If now it is desired to turn a locomotive which is standing in the position of the dart _A_, it is run on the curve _A C_ to the position of the darts _a_ and _C_. It is then run backward from _C_ on the curve _C B_, as represented by the dart _b_, and when it reaches the main track in the position of the dart _B_ it is evident that its position will be reversed, as is shown if we compare the direction of the dart _A_ with that of _B_. PART XXVI. INSPECTION OF LOCOMOTIVES. QUESTION 455. _What are the principal divisions of the work of operating or running a locomotive?_