Monocular Compound Microscope by Crichton, c. 1840

John Crichton, England. Engraved "Improved Compound Microscope by Crichton, 112 Leadenhall St. London", brass, folding tripod base, support pillar base with compass joint opening for the 1 ¾-in. concave mirror, unusually deep sprung stage, 2-in. cylinder body mounted on cantilever arm, triple-lens system with Huygenian-type eyepiece, two plano-convex lenses and biconvex field lens, rack-and-pinion focusing to the inner tube, height 17 in. Accessories including 7 objective lenses (nos. 0, 1, 2, 3, 4 and 6), Lieberkuhn, live box, 2 bone slide, 6 wood slide, 3 with opaque objects, stage forceps and separate stand for the bull's-eye condenser and candle holder, in fitted mahogany case with detachable tray and brown velvet lining in lid.

布雷克拍品等级是为了方便竞买人判断拍卖品的成色而设置的。布雷克等级用1到6级来标注外观和功能的成色，(从非常好到非常差)。 在目录图册里用括号里的2个数字来表示，前一个数字表示外观成色的级别，后一个数字表示功能成色的级别。如(3/2)表示外观成色是3(满意的)，功能成色2(好)。 成色 定义参照下列标准： 1 - 非常好 (未使用过，没有使用痕迹) 2 - 好 (新，极少的使用痕迹) 3 - 满意的 (普通的使用痕迹) 4 - 及格的 (明显的使用痕迹，某个非主要部件是后配的) 5 - 有缺陷的 (极明显的使用痕迹, 某个主要部件是后配的，功能上有缺陷，需要修理) 6 - 非常差 (严重破损, 缺少重要部件)