His "Haüy construction" approximates an octahedron by accreting concentric layers of cubes onto a central cube; the centered octahedral numbers count the number of cubes used by this construction.
His "Haüy construction" approximates an octahedron by accreting concentric layers of cubes onto a central cube. The centered octahedral numbers count the number of cubes. These cubes are used by this construction.