,00 SUMMARY OF CURRENT RESEARCHES RELATING TO 



vides a current of 4 amperes, and 1ms rack feed and centring adjust- 

 ment. It lias also extension gear for adjusting the carbons while the 

 image on the screen is being observed. 



I (4) Photomicrography. 



Wychgram, E. — Aus Optischen und mechanischen Werkstatten iii. 



[The author gives a very interesting sketch of the progress and develop- 

 ment of instruments connected with projection and photomicrography 

 during the last two years.] 



Zeitschr. wiss. Mikrosk., xxviii. (1911) pp. 59-69 (6 figs.). 



(5) Microscopical Optics andiManipulation. 



Observations on the Technical Execution and Biological Real- 

 ization of Microscopical Measurements.*— R. von Lenderfeld reminds 

 his readers of the great variability in the magnitudes both of crystals of 

 the same chemical composition and of organisms of the same species. 

 The difficulty of appropriately measuring them is therefore so great that 

 the only sound method must be biometric. Thus, for example, the 

 magnitudes of spicules and such like should be stated in relation to the 

 magnitudes of the parent body. This would obviously require a great 

 many measurements ; but the measurements could, however, be plotted 

 out on a curve and so afford a realization of their biological value. He 

 has, therefore, contrived a measuring apparatus susceptible of great accu- 

 racy, and so arranged that a skilled worker can make a large number of 

 successive observations and dictate them to an assistant. He projects 

 the microscopic image on to a large plane mirror which reflects the 

 image back on to a fixed matt glass screen of about 4 sq. m. in size. 

 The mirror has universal adjustment, so that the image, which is of course 

 a much enlarged one, is brought to a convenient spot on the screen in 

 front of the observer's seat. The Microscope is so placed that the ob- 

 server is able, without leaving his seat, to regulate the movements of the 

 object on the Microscope stage. The dimensions of the image on the 

 matt screen are ascertained by the use of scales specially drawn on tracing 

 linen. An objective micrometer is used in the Microscope, and thus the 

 proportion of image to object is known. A large number of measure- 

 ments on one object, or on a group of similar objects, can be quickly 

 and easily made, the results being dictated to an assistant who sits at a 

 table behind the observer. The author has found his method give very 

 satisfactory results. 



Opacity of Certain Glasses for the Ultra-violet.f — L. Bell has 

 examined the spectra yielded by ultra-violet rays after transmission 

 through specimens of various kinds of glasses. Photographs are given of 

 the results, which vary very much in opacity. The light-source used was 

 a quartz mercury lamp. 



16) Miscellaneous. 



Some New Diatomic Structures discovered with a New Zeiss 

 Apochromat4— A. A. C. E. Merlin describes the results of his use of a 



* Zeitschr. wiss. Mikrosk., xxviii. (1911) pp. 27-34 (3 figs.). 



t Proc. Amer. Acad. Arts and Sci., xlvi. (1911) pp. 671-80 (2 pis.). 



J Journ. Quekett Micr. Club, 1911, pp. 199-202. 



