ZOOLOGY AN1> BOTANY, MICROSCOPY, ETC. 



693 



Recent Progress in the Construction of Mineralogical and Metal- 

 lurgical Microscopes.* — E. Sommerfeldt treats of this subject with 

 especial reference to the last decade. The following are the titles of his 

 sections and sub-sections : — 



1. The Petrographic Microsco/>e.—Widti-SLng\e& types ; improvements 

 in the condenser ; microscopes with simultaneous rotatory nicols. 



•1. The Grystallographic Microscope. — Stands for observations at high 

 temperatures ; stands for universal (rotatory) methods. 



8. The Metallo graphic Microscope. 



4. Microscopical Auxiliaries. — Condenser and ^nr= 

 ocular ; heating apparatus ; hardness measure- JP , 

 ments ; accessories for metallographic microscopy. 



(2) Eye-pieces and Objectives. 



Fig. 78. 



Allan's Variable Eye-piece. — This eye-piece 

 (fig. 78) was fully described by Mr. Conrad Beck 

 at "the June Meeting (see Proceedings, ante, 

 p. 570). 



(3) Illuminating' and other Apparatus. 



History of the Cardioid Condenser : Memo- 

 randum on the Leitz Mirror Condenser.f — In 

 order to correct a somewhat ambiguous refer- 

 ence in A. Gdeichen's Die Theorien der modernen optischen Instru- 

 mente,| W. v. Ignatowsky supplies the following information about the 

 cardioid condenser. He states that Siedentopf's cardioid was first de- 

 scribed in September, 1900, but that his (Ignatowsky's) had been actually 

 placed on the market by Leitz in October, 1907, and its theory had been 

 published in 1908. It has, in fact, been shown by Sckwarzschild,§ as 

 Siedentopf admits, that the cardioid condenser is a special case of a more 

 general construction. The author gives an outline of Schwarzschild's 

 investigation. 



Apparatus for Microscopical Observation of Frozen Objects. || 

 E. Schaffnit's cold-chamber is constructed out of a rectangular metal 

 box, 9 by 2 cm. and 2 '5 cm. deep. The glass lid slides in a groove, and 

 is perforated for reception of the Microscope objective ; the metal floor 

 is similarly perforated for receiving the condenser (fig. 79). The object- 

 carrier d, about 15 cm. long, slides through a slit in the side wall c, and 

 is steadied by two clips. The side walls are perforated for the escape of 

 the carbonic acid vapours. A suitably graduated thermometer g passes 

 through the front wall. Two watch-glasses for ether are placed on the 

 chamber-floor, and are filled with a pipette. There is a suitable 

 tube-attachment to a carbonic acid steel cylinder ; it is desirable to 



* Zeitschr. wiss. Mikrosk.. xxviii. (1911) pp. 70-82. 

 t Zeitschr. wiss. Mikrosk., xxviii. ( l'Jll) pp. 50-55 (2 figs.). 

 J Stuttgart : F. Enke, p. 248. 



§ Abhandl. d. Kgl. Gesell. d. Wiss. z. Gofctingen, Math. Physik. Klasse : IV. 

 " Untersuchungen zur geometrischen Optik ii." 



|| Zeitschr, wiss. Mikrosk., xxviii. (l'Jll) pp. 45-8 (2 figs.). 



