163. =Object Marker.= This is designed to indicate the exact portion of an object which has been seen in the field of the microscope. After finding the required field, the objective of the microscope is unscrewed and the marker is screwed into the tube in its place. By then moving the tube so that the marker comes in contact with the object that portion of the object which occupied the optical axis of the microscope is indicated =1.25= 164. =Object Marker= with diamond point, by means of which the object can be marked by drawing a circle =4.--= 165. =Demonstration Ocular= of Kuznitzky (Cf. Zeitschr. f. wissensch. Mikroskopie, XIII, 1896).--Indicates any particular portion of the image to which it is desired to draw particular attention. A small lever at the top of the ocular moves an indicator just above the diaphragm of the ocular to any part of the field =3.25= [Illustration] 166. =Opaque Illuminator=, for illuminating polished pieces of metal whose structure is to be investigated by means of high power objectives--A collar, carrying a prism, screws into the tube of the microscope, and by means of the prism sufficient light is thrown through the objective upon the otherwise opaque object to permit of its examination up to 1000 diameters magnification =6.--= 167. =Erecting Prism=--This is fastened over the ocular and erects the image received from the compound microscope, thereby materially assisting any dissection or other operation on the stage of the microscope =7.25= [Illustration] 168. =Microscope= for the accurate reading of thermometer scales, after Fridtjof Nansen. Stand with spring-clamp to attach thermometers of various sizes. With micrometer ocular and objective magnifying 12 times =20.--= [Illustration: Saccharimeter No. 169.] 169. =Saccharimeter=, Mitscherlich's (improved form), for determining the amount of sugar contained in liquids, glucose etc. by measuring the angle of rotation. Tube with concave mirror on stand, graduated scale with vernier and lens for reading one-tenth of a degree of rotation. The rotation of the Nicol prism with the vernier is performed by means of an endless screw. The adjustment is accomplished as soon as the two squares of the divided quartz-plate show the same color. Two tubes of 100 and 200 mm length, for the liquid to be examined, are supplied with the apparatus. Should the rotation of the substance examined be excessive, it is necessary to use sodium light for illumination =52.--= =Microscopical cases.=