548 SUMMARY OF CURRENT RESEARCHES RELATING TO 



considered as endorsing any practical value in the instrument as a 

 whole. 



The principal micrometric movement is controlled by the gradu- 

 ated milled head A working on a fine steel screw against springs, by 

 which the rectangular framework carrying the optical body is moved in 

 a direction at right angles to the vertical main limb and parallel with 

 the stage. The optical body, with rack and pinion for coarse adjust- 

 ment, fits loosely into this carrier ; it can be adjusted concentrically 

 with the rotating stage by the action of side screws together with the 

 micrometer-screw at A, and can be clamped in position by a screw- 

 collar beneath. The fine-focussing is effected by the micrometer-head 

 B working on a screw against a spiral spring on the main limb ; the 

 whole of the optical portion is thus moved together in focussing, as is 

 usual in Continental Microscopes. The eye-piece has a goniometer 

 circle C attached, and is provided with a movable disk of glass with 

 crossed lines in the usual position of the eye-piece micrometer, by 

 which accurate determinations of angles in azimuth can be made 

 while the object is stationary, &c. The rotating stage is of simple 

 construction, similar to that on ordinary " turntables " ; it is held in 

 position by an indented key-piece (metal knob shown under stage) 

 that slides into a circular rotating groove beneath, and can be removed 

 at pleasure — the main rectangular stage is then only T 3 ^th inch in 

 thickness, and is fitted with a wheel of diaphragms, also removable. 

 The mirror D is mounted in a gimbal sliding on a bar with latera 1 

 motion ; the three axes of motion are each provided with a graduated 

 disk and pointer, so that exact record of the position can be made. 

 The condenser E is mounted to slide on one of the feet, and can be 

 adjusted variously to direct the light upon the mirror. The two back 

 feet close up against the front one for convenience of packing. 



Simplified Reading Microscope for horizontal and vertical 

 circles.* — Herr Hensoldt, of Wetzlar, claims to have made a great im- 

 provement in the application of the compound Microscope to instruments 

 of medium size, such as theodolites of from 12 to 20 cm. in diameter 

 of limit. Whilst universally used for the larger, especially astrono- 

 mical instruments, a Microscope has been found to be inconvenient 

 for others, principally on account of the projecting micrometrical 

 screws and the length of the body hitherto found necessary. 



The author says that he " has succeeded in reducing the length of 

 the Microscopes to a most considerable extent by the selection of 

 favourable qualities of glass, and by suitable construction of the 

 lenses. With a power of from 45 to 50 diameters, they only 

 possess a length of 5 cm. and an outer diameter of 16 mm., reading 

 up to 12", and between the objective and the division there is suffi- 

 cient room to affix a little illuminator, which throws a more than 

 sufficient amount of light on the division. The latter appears very 

 clear and distinct, and if the limb is provided with a glass cover, the 

 objectives of the Microscopes are constructed accordingly, so as not 

 to lose in definition. 



* Zeitschr. f. Vermessungswesen, viii. Transl. in Eng. Mech., xxxiv. (1881) 

 pp. 83-4 (1 fig.)- 



