630 SUMMARY OF QUERENT RESEARCHES RELATING TO 



excellent results, but with thick or obscure specimens 60 seconds might 

 be required. When full solar light was not obtainable the investigators 

 used arc-light. 



ScHEFFEE, W. — Microscopical Researches on the Effect of the Persulphate and 

 Ferricyanide Reducers, as also on the Re-developing of 

 Bleached Negatives with Alcoholic Developers. 



Brit. Journ. Photog., liii. (1906) pp. 964-5 (9 figs.) 



,, ,, Note on the Reversal of Solarised Negatives with Farmer's 



Reducer. Tom. cit., p. 1027 (2 figs.). 



„ „ Microscopical Researches on the Size and Distribution of Plate 



Grains. Oj). cit., liv. (1907) pp. 116-20 (19 figs.). 



,, ,, Microscopical Researches on the Plate Grain. 



Tovi. cit., pp. 271-3 (7 figs.). 



Hansen, P. C, C. — Einige Farbfilter, sowie einige histologische Farbungen fiir 

 mikrophotographische Aufnahmen. 



[The author's experieuce leads him to recommend certain solutions.] 



Zeitschr. wiss. Mikrosk., xxiii. (1907) pp. 410-14. 



Fran^ois-Franck, Ch.-A. — Note generale sur les prises de vues instantanees 

 microphotographiques (plaque fixe a peUicule) avec Tare volta'ique. 



C.R. Soc. Biol. Paris, Ixii. (1907) pp. 637-9. 



(5) Blicroscopical Optics and Manipulation. 



Ultramicroscopic Studies on certain Organic Colloids. Two Optic 

 States of Organic Colloids.* — A. Mejer, under the above title, describes 

 a series of experiments which show that organic colloids can be met with 

 in two states optically different, viz. hydrogels, solidiiied or liquefied, 

 relatively homogeneous ; hydrosols, showing numerous granules. One 

 state may be transformed into the other, and in the course of this trans- 

 formation arise the solutions of " globulines " and of " albumine." 



New Method of Determining Indices of Refraction.f — Gr. Cesaro 

 employs for this purpose WoUaston's goniometer, without the use of any 

 other special apparatus. Instead of deducing the index of refraction 

 from observation of the angle of minimum deviation, the author pre- 

 viously determines on a certain deviation 2a. He then determines by 

 the goniometer the two positions, on alternate sides of the minimum 

 deviation, in which the refracted ray undergoes this said deviation. The 

 angle «, through which the prism must turn about its edge to pass from 

 one position to the other, the angle cf> of the prism, and the deviation 2a, 

 suffice for the calculation of the refractive index. The author gives a 

 full account of the details and calculations. 



Direct Visibility of Neutral Layers in Bodies supposed to con- 

 tain them. J — H. Siedentopf has succeeded in taking photographs of 

 these under several conditions. One of his experiments was to bend a 

 strip of plane-parallel glass, so that the middle part in cross-section was 

 made semicircular, some of the original plane remaining as bilateral 



* C.E. See. Biol. Paris, Ixii. (1907) pp. 42-4. 



t Bull. Classe Sci. Acad. Roy. Belgique, 1907, pp. 135-162 (10 figs.). 

 X Pamphlet reprinted from the Zeit. des Osterr. Ingenieur- und Architekten- 

 Vereines, Iviii. (1906) No. 33, Vienna (10 pp.). 



