624 SUMMARY OF CUKRENT RESEARCHES RELATING TO 



of this latter is divided to read direct to O-Ol mm. This divided head 

 is of use in obtaining the correct position for viewing the profile of a 

 screw thread. To effect this the top of the thread is focused on the 

 cross-wires of the ocular, and the body is lowered bj means of the fine- 

 adjustment an amount equal to the secant of the angle through which 

 the screw is tilted on the stage multiplied by half the maximum diameter 

 of the thread. 



The object is illuminated by means of a mirror or an opal plate, 

 which are mounted with universal motions. An iris-diaphragm, which 

 is of the greatest convenience for controlling and modifying the light, 

 is fitted between the mirror and the stage. This diaphragm can be 

 instantly swung aside if it be not required ; when it is brought back to 

 the optic axis, the exact position is indicated by a spring click. 



Extremely large objects, sach as milling cutters, hobs up to 2 J in. 

 diameter, can be accommodated on the instrument by means of special 

 arms attachable to the stage which hold adjustable male and female 

 centres. 



Museum Demonstration Microscope.* — G. Marktanner Turneret- 

 scher describes a Microscope, which is in use in the zoological and 

 botanical section of the Joanneum in Graz. It renders microscopical 

 preparations accessible to the general public, inexpert in the use of 

 apparatus. The instrument is enclosed in a cabinet, 45 in. in height. 

 An object-carrying disk. 12 in. in diameter, revolving round a vertical 

 axis, is arranged to hold fourteen microscopical specimens. By turning 

 a screw-head on the right-hand side of the cabinet, the disk is caused to 

 revolve. This movement can only take place in one direction. A 

 spring-catch, working on the circumference of the disk, checks the 

 movement when the specimens are in the correct position for inspection. 

 Two Microscope tubes emerge from the top of the cabinet, a low-power 

 and a high-power. While one slide is in position under the low-power, 

 the neighbouring slide is under the high-power. Both are in correct 

 focus for the normal eye, but to allow for individual variations, a lever 

 is placed to the right of the eye-pieces, which, being moved forwards or 

 backwards cants the object-disk within a limited range, and so shortens 

 or lengthens the focus. Transmitted light is used for most preparations, 

 but for opaque objects requiring reflected light, a small electric bulb is 

 placed over the disk. This is automatically switched on when an opaque 

 object comes into position under the low-power tube. In the left-hand 

 part of the cabinet is a vertical drum, revolving on a horizontal axis, 

 carrying descriptions of the preparations. It is geared to revolve with 

 the object-disk so that as each pair of specimens comes into position 

 under the Microscopes, the letterpress descriptive of them becomes 

 available for study. 



(2) Eye-pieces and Objectives. 



Reichert's New Comparison Eye-piece.f — This optical device (fig. 

 86) serves for comparing, by means of a single eye-piece, two objects 



* Museumskunde, ix. (Berlin, 1913) pp. 158-62. 

 t C. Reichert'8 Special Catalogue, 1913 (3 figs.). 



