498 SUMMARY OF CURRENT RESEARCHES RELATING TO 



drums with common index, and there is a separate scale for the milli- 

 metres. The Microscope has a simple ocular, with strong threads, and 

 three objectives giving 10-100 diameters. The ocular is rotatory 

 through 90°, and stronger objectives can be used if desired. 



Toepfer's Universal Measuring Apparatus.* — The description given 

 of this instrument (fig. 128) by A. Wolfer states that it is intended for 

 the measuring of photographic star-plates of all kinds, as well as for 

 other purposes requiring exact measurement, such as the examination of 

 micrometer screws. 



A desk-shaped protuberance a standing on an iron base-plate has its 

 upper surface inclined to the observer at an angle of 45°, and carries the 

 object-stage and the horizontally placed and horizontally working main 

 measuring-screw. In front of the protuberance a, and partly extending 

 over it, there is a very strong bearer b b, stiffened with ribs and bowed 

 at its centre ; the lower part of the bearer is vertical, and its upper 

 part is parallel to the object-stage, the Microscope being applied to it in 

 a slide, and receiving, by means of a screw, a movement perpendicular to 

 the movement of the object-stage. Thus the whole arrangement pro- 

 vides a very convenient attitude for the observer. There are means for 

 levelling the instrument as a whole. The object-stage c is a glass plate 

 fastened on to a square bronze frame, and works by means of four pins 

 on a circular metal plate, whose circumference forms a position circle, 

 and is graduated to half-degrees, and reads to minutes by means of two 

 verniers diametrically placed. This position circle is rotatory in a strong 

 cast-iron ring concentrically set beneath it, the verniers, as well as a 

 tangent-screw, being attached to the ring. The measuring stage and 

 all its parts are operated by the horizontal main screw, and may be 

 moved in the direction of its axis. This screw is very strong, and is 

 carefully designed for its double purpose of movement and measurement, 

 the diameter of its thread being 10 mm., its thread-distance 0*5 mm., 

 and the whole action range 100 mm. • There are two drums (the right- 

 hand one is shown in figure) near the screw-handle, and these give the 

 whole rotations and hundredths, so that the accuracy of the direct 

 reading extends to ttoVo mm. A scale g, divided into millimetres, and 

 an index moving with the measuring stage, give the actual position at 

 any moment in millimetres. In addition to the ordinary handles for 

 the rotation of the screw, there is a disk h of 7 cm. diameter with 

 finger openings ; this disk is outside the drum, and serves for quick 

 rotation when rapid transport of the measuring stage over large dis- 

 tances is required. Means are provided whereby the weight of the 

 stage is taken off the screw and thrown on to ball bearings working in 

 grooves in the desk-shaped frame. The glass plate is 16 by 16 cm. ; 

 smaller plates may be fixed, so that they lie centrically with the position- 

 circle. 



When it is desired to examine a micrometer screw, the glass plate is 

 removed and replaced by a hollowed-out bronze plate with a circular 

 aperture of 50 mm. diameter. This bronze plate is provided with a 

 screw-thread, and receives the micrometer, whose ocular has been 



* Zeitschr. f. Instrumentenk., xxvii. (1907) pp. 297-301 (1 fig.). 



