DIPHTHONG, in grammar, a double vowel, or the mixture of two vowels pronounced together, so as to make one syllable. The Latins pronounced the two vowels in their diphthong DIOPTRICS. Fig. 1. A diagram showing a lens system. Light rays from point F converge through a lens G to point A. The lens is represented by an oval shape. Fig. 3. A diagram showing various lens shapes: a concave lens (E), a biconcave lens (D), a biconvex lens (C), a convex lens (B), and a plano-convex lens (A). Light rays are shown passing through these lenses, with labels X, Y, Z, and V indicating different points or rays. Fig. 13. A diagram of a horizontal bar with points A, B, C, D, E, F, G, H, and I marked along its length. A line segment connects point A to point I. Fig. 6. A diagram of a table with a funnel-shaped structure underneath. The table has legs labeled F and F. The funnel structure has points labeled A, B, C, D, E, G, H, I, K, L, M, N, and O. Fig. 2.DIVISIBILITY. A diagram showing a curve and points labeled A, B, C, D, E, F, and G. The curve starts at point B and ends at point G. Fig. 7. A diagram of a cabinet with a funnel on top. Inside the cabinet, there is a fire. The cabinet has points labeled A, B, C, D, E, F, G, H, I, K, L, M, N, O, P, Q, R, and S. Fig. 12. A diagram of a cabinet with a lamp on top. Inside the cabinet, there is a fire. The cabinet has points labeled A, B, C, D, E, F, G, H, I, K, L, M, N, O, P, Q, R, and S. A. Bell. Sculp.t Fig. 4. A diagram of a rectangular container with a circle on top. Inside the container, there is a fire. The container has points labeled A, B, C, D, E, F, G, H, I, K, L, M, N, O, and P. Fig. 10. A diagram of a tall, ornate structure with a fire at the top. The structure has points labeled A, B, C, D, E, F, G, H, I, K, L, M, N, O, P, Q, R, and S. Fig. 11. A diagram of a cabinet with a funnel on top and a fire inside. The cabinet has points labeled A, B, C, D, E, F, G, H, I, K, L, M, N, O, P, Q, R, and S. Fig. 8. A diagram of a landscape with points labeled A, B, C, D, E, F, and G. Fig. 9. A diagram of a landscape with ships, labeled A and B.