anchoring the drum firmly to the latter. Oil-grooves must be provided where these plates bear on the centre casting. Fillers are to be used beneath all stiffeners on drum.

The drum must be assembled and the bottom must then be planed smooth so as to provide an even bearing for the upper track. If it is not practicable to plane the entire drum at once, then each segment thereof is to be planed separately ; but in this case the greatest care is to be taken to make the assembled parts form a perfect whole.

The least thickness of metal to be used for bottom flanges of drum shall be three quarters (3/4) of an inch, so as to provide ample metal for planing off the bottom, and that for the web and top flanges one-half (1/2) inch.

The upper track shall be made of segments of sufficient thickness to distribute the load properly between the rollers and the drum. The top face of this track shall be planed smooth so as to form close contact with the bottom flange of the drum, and the lower face shall be planed conical so as to fit closely to the conical rollers. All joints between segments are to be planed smooth and to such bevel as to ensure perfect contact with each other. These track segments are to be riveted or bolted to the bottom flanges of the drum with fifteen-sixteenths (15/16) inch rivets or bolts, placed opposite, and spaced not to exceed fifteen (15) inches between centres. The heads of these bolts or rivets are to be countersunk in the track on the side next to the rollers.

No rust-cement or any other composition is to be used between the track and the drum.

The lower track is to made strong enough to distribute the load from the rollers uniformly over the masonry. The bending moment on the lower track is to be found by the formula

where M = greatest bending on lower track, W = total load on one roller, and l = distance from centre to centre of adjacent, rollers, measured on the centre line of the track.

The greatest allowable tensile stress on the extreme fibre for