500 SUMMARY OF CURRENT RESEARCHES RELATING TO 



360°, and the other is limited to 90°. Two pieces of measuring apparatus 

 are applied to the flange, one being a simple eye-piece with two parallel 

 threads. One of these threads is fixed, and the other can be adjusted 

 to or from it ; a third thread is perpendicular to both. The movable 

 thread can be set at any distance from the fixed thread, suitable for the 

 examination of the object under consideration, and is used in connexion 

 with the stage screws. It will be seen that this arrangement would 

 facilitate, for example, the testing of a micrometer screw. The com- 

 binations of oculars and objectives allow of magnifications between 

 2 and 100-fold. In place of the above described ocular, an ordinary 

 micrometer is also provided, having two double threads perpendicular 

 to one another, and operated by two micrometer screws r and s, of 

 0*25 mm. range. Thus simultaneous measurements of right-angled 

 co-ordinates can be made. There is an arrangement for bringing the 

 origin of co-ordinates into the centre of the field. 



Gebhardt, W. — Aus Optischen und mechanischen Werkstatten. 



[The author reviews the chief German modern microscopes and their 

 auxiliaries — most of which have been already noticed in our Journal.] 

 Zeitschr. wiss. Mikrosk., xxiv. (1908) pp. 396-421 (15 figs.). 



Rohr, M. v. — Die binokularen Instrumente nach Guellen bearbeitet. 



Berlin : Springer, viii. and 223 pp. 70 figs. 1 tab. 



Schwarzmann, M. — Sammlungsmikroscope und Mineraliensammlungen. 



Centralbl. Mineral. Geol. it. Palaontol., 1907, pp. 615-24 (3 figs.). 



(.3) Illuminating and other Apparatus. 



History of Mirror-Condensers.* — H. Siedentopf collects and de- 

 scribes all the various forms of mirror-condensers which have appeared 

 since J. B. Reade invented the first in 1837. He enumerates in all 

 some sixteen varieties, some of which have been more than once " dis- 

 covered." Thus, J. W. Stephenson's "Catoptric Illuminator" (1879), 

 came out as "Reichert's Speigelkondensor " in 1906. The author points 

 out that, with the invention of Abbe's illumination apparatus, the 

 catoptric condenser passed into oblivion, although it possessed the 

 conspicuous advantage of not decomposing the light. The advent of 

 ultramicroscopy has again drawn attention to the subject in the hope 

 that the scope of the new method may thereby be widened. Zeiss' 

 rock-crystal paraboloid for obtaining dark-ground illumination with 

 ultra-violet light is described, but the author concludes his paper by 

 remarking that mirror-condensers can only avail to a very limited 

 extent, as compensation for the more complete installations for the 

 examination of ultramicroscopic particles. 



Reichert's New Large Projection Apparatus.! — In describing 

 this instrument, O. Heirnstadt says that great care has been taken to 

 meet the three essentials of projection apparatus, viz. (1) that bright 

 images should be obtained ; (2) that all kinds of projection in ordinary 

 use should be obtainable ; (3) that the change-over from one kind of pro- 

 jection to another should be expeditious. The first requirement is met 

 by the use of an arc lamp with the carbons mutually perpendicular, 



* Zeitschr. wiss. Mikrosk., xxiv. (1908) pp. 382-93 (16 figs.), with a bibliography 

 of some 30 references. t Tom. cit.. pp. 370-81 (7 figs.). 



