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least ground-space of all engine-house designs ; but it has the same disadvantage compared witha track-approach system as a turn-table system has, namely, a breakdown of the transfer-tableor of the turn-table, or a blockade on the open track leading immediately to or from the table,will cause a serious blockade of the entire business of the road, similar to the consequences of anaccident on the main track. The track-approach system has the decided advantage of offeringless opportunities for a general blockade, and it allows engines to be removed very quicklyfrom the house in case of fire.
The usual style of an engine-house, known in this country as a roundhouse, consists of ahouse built in a circular form around a turn-table, with tracks leading from the turn-tableradially into the house. The building can either be built as a full circle, known as a closed orfull-circle roundhouse, or it can be a segment of a circle, known as an open or segmental round-house. The walls of the building are not actually built circular, but in the shape of a polygon,the circle being divided up into stalls or panels, the walls in each panel being built on the chordsconnecting the panel points. It is customary to provide two passage-ways into a closed round-house, through two of the stalls, so that in case of a block on one track the other track can beused. Two approach tracks to the turn-table are also frequently introduced in a segmentalroundhouse, but in this case they do not usually run through the building, but in frontof it, so that all stalls in the building are available to stand engines. The passage-waysto the turn-table through a closed roundhouse are walled on each side, so as to act as fire-walls and allow the house to be heated better in winter. In addition, in large engine-houses,special fire-walls are introduced, so as to divide the interior of the building into several parts,retarding thereby the spread of a fire throughout the building. Where the ground-space isavailable, it will be found more economical to place the building as far au'ay from the turn-table as feasible, as a larger number of engines can be thereby accommodated under the sameroof surface, while in case of fire the engines can be run out of the stalls in front of thetracks. The size of the house can generally be so selected, that the engines on every otherstall can be-run out of the house without interfering with each other, which feature offers theadditional advantage, that surplus engines can stand temporarily between the house and theturn-table, when the house is full. Segmental polygonal houses have been built withtrack approach in place of a turn-table. This method offers all the advantages of aspecial track approach, but it is only feasible where the necessary ground-space is available,and as, usually, where a large engine-house has to be built a turn-table is required anyhow forthe turning of engines, it seems more correct to always place a turn-table in combinationwith a roundhouse.
The advantages of a square house with special track approach are, that delays from break-downs, blockades, or loss by fire are not so liable to occur; the house is cheaper and simpler tobuild, especially for a small house with only a few stalls; and the engine-house foreman willhave a better oversight over the whole building than in a roundhouse,—which is quite impor-tant where there is considerable u'ork and repairs to be done around the engines. But thedisadvantage of a track approach is that it takes up considerable ground-space.
The advantages of a square house with a transfer-table are, that it takes up proportionatelythe least ground-space of any system ; a cheaper and simpler house can be built; a better over-sight had of the work going on in the building than in a roundhouse ; and the extension of