766 SUMMARY OF CURRENT RESEARCHES RELATING TO 



cell-axis ; (5) that it is possible in many cases of equal chemical com- 

 position and equal morphological formation to distinguish histological 

 elements from one another in polarised light. 



Visual Purple.* — J. Von Kries considers that visual purple is a 

 substance which supplies the retinal basis for vision at low luminosities, 

 and the accumulation of this substance is accountable for the great 

 increase in sensitiveness of the dark-adapted eye— a thousand-fold 

 increase according to some computations. 



Some Experiments with Actinic Light.f — J. W. Kime, with the 

 object of furthering the application of coloured light in therapic treat- 

 ment, has conducted some experiments for the purpose of localising 

 those bands in the solar spectrum which are rich or poor in actinic rays. 

 Strips of glass, corresponding in colour to the various tints of the 

 solar spectrum, were placed in a frame, bound to a sensitised plate, and 1 

 exposed almost instantaneously to very weak diffused daylight, which 

 entered the dark room without passing through glass. The result is 

 shown in fig. 1, plate VIII., which is a negative plate. The open space 

 and the plain glass strip, which were also provided, when compared with 

 the blue glass present very little difference, the plain glass being a shade 

 darker, showing that less actinic light passed through it than through 

 the other two. It was found that no light whatever reached the plate 

 through the red, and no trace is apparent in the orange ; the yellow 

 transmits an appreciable amount ; and the green just enough to be seen. 

 From this point we jump from almost zero in the green to 100 p.c. in the 

 blue. Hence wave-length has nothing to do with determining the 

 chemical activity of the light. In the indigo there is a slight diminution 

 from the blue, but there is still fully as much as traversed the plain' 

 glass. In the violet we drop back to about the same percentage us in 

 the yellow. It is apparent from the photographs that colour, independ- 

 ently of wave-length, influences the chemical action of light. Fig. 2, 

 plate VIII., which is a positive, is in every sense confirmatory of the con- 

 clusions drawn from fig. 1, but was produced in a directly opposite manner. 

 The same strips of glass as before were again used, but were placed over 

 ordinary photographic printing paper, Aristo, and were exposed to the 

 sun until the open space was fully printed. No other glass intervened 

 between the sensitised paper and the sun except the strips referred to. 

 Experiments were also made to test the penetrability of actinic light 

 through the tissues of the human body. 



Kbu8h, H. A. — Die Durchlassigkeit einer Anzahl Jenaer optischer Glaser fur ultra- 

 violette Strahlen. Zeit.f. Instrumentenkunde, XXIII. (1903) pp. 197-207, 



4 figs (July) ; and pp. 229-239, 3 figs. (August).. 



Siedentopf, H., & R. Zsigmondt — tiber Sicbtbarmachung und Grosser-- 

 besiimmung ultramikroskopischer Teilcbeu, mit besorderer Anwendung auf 

 Goldrub ing laser. 



[The- suhstiince of this pamphlet was given to the Society at the Meet- 

 ing on June 17, 1903. and is reported in the Proceedings for that date.] 



S.A. Physik. Vierte Fol<,e. X. (1903) 39 pp. 

 A copious French abstract of the preceding appears in the Bibliotheque Universelle 

 (Arch. Set. Phys. et Nat.), XVI., Geneva, 1903, pp. 130-8. 



* Ahhandl. z. Physiol, d. Gesichtsenipfindun°;en, 1897, pp. vi. and 198; 1902 

 p. 197. Leipzig. 



t Scientific American, quoted in English Mechanio, lxxviii. (1903) pp. 478-9* 

 (3 figs). 



