Archibald Scott Couper's bond lines in a French version of his 1858 paper. On the left is his representation of tartaric acid and the product obtained after the loss of water by heating. On the right is the first depiction of a ring system—for cyanuric acid (Az =N). Here Couper used continuous lines and brackets to represent bonds. In other publications, bonds are straight dotted lines—possibly the typesetter's preference. From Annales de chemie et de physique, Série 3, 53 (1858), 488–489. Chemical Heritage Foundation Collections.