Abstract: An aerator for mixing an ambient gas with a liquid and agitating the liquid incorporates at least three bearings that are rigidly connected to an aerator housing. A propeller is driven by a central shaft that is rotatably mounted in the aerator housing using the bearings. Two bearings are located near the ends of the central shaft. At least one additional bearing is located between the ends, for example, in a intermediate position. This additional bearing may absorb some of the force that would otherwise be transferred to the bearing near the propeller end of the central shaft. The bearings are thus subjected to lower stress and may exhibit a prolonged useful lifespan.

Abstract: A block for use in constructing a retaining wall having a bottom with a non-planar portion which creates a gap between the bottom surface and the top surface of a lower course of similar blocks when the block is placed thereon. Preferably, the block's bottom surface further comprises a plurality of grooves. It is envisioned that these grooves be “V” shaped, thereby having angled walls which act to funnel the larger stones into an area of adequate clearance when the block is being placed on a lower course of similar blocks.