Fig. 34 represents a portion of the interior of this cooking-stove. First, notice the fire-box, which has corrugated (literally, wrinkled) sides, by which space is economized, so that as much heating surface is secured as if they were one third larger; as the heat radiates from every part of the undulating surface, which is one third greater in superficial extent than if it were plane. The shape of the fire-box also secures more heat by having oblique sides--which radiate more effectively into the oven beneath than if they were perpendicular, as illustrated below--while also it is sunk into the oven, so as to radiate from three instead of from two sides, as in most other stoves, the front of whose fire-boxes with their grates are built so as to be the front of the stove itself. [Illustration: Fig 35. Model Stove] [Illustration: Fig 36. Ordinary Stove] The oven is the space under and around the back and front sides of the fire-box. The oven-bottom is not introduced in the diagram, but it is a horizontal plate between the fire-box and what is represented as the "flue-plate," which separates the oven from the bottom of the stove. The top of the oven is the horizontal corrugated plate passing from the rear edge of the fire-box to the back flues. These are three in number--the back centre-flue, which is closed to the heat and smoke coming over the oven from the fire-box by a damper--and the two back corner-flues. Down these two corner-flues passes the current of hot air and smoke, having first drawn across the corrugated oven-top. The arrows show its descent through these flues, from which it obliquely strikes and passes over the flue-plate, then under it, and then out through the centre back-flue, which is open at the bottom, up into the smoke-pipe. The flue-plate is placed obliquely, to accumulate heat by forcing and compression; for the back space where the smoke enters from the corner-flues is largest, and decreases toward the front, so that the hot current is compressed in a narrow space, between the oven-bottom and the flue-plate at the place where the bent arrows are seen. Here again it enters a wider space, under the flue-plate, and proceeds to another narrow one, between the flue-plate and the bottom of the stove, and thus is compressed and retained longer than if not impeded by these various contrivances. The heat and smoke also strike the plate obliquely, and thus, by reflection from its surface, impart more heat than if the passage was a horizontal one.