256 SUMMARY OF CURRENT RESEARCHES RELATING TO 



(6) Miscellaneous 



Strehl's Theory of the Microscope : the Pleurosigma Image.*— 

 Herr Karl Strehl produces an article on the pleurosigma as a further 

 contribution to his writings on the theory of the Microscope.^ He 

 desires to show that a knowledge of the diffraction theory is necessary 

 to the proper comprehension of microscopic perception, aud also that 

 the theory may lead to the detection of some of the most delicate 

 features of the image. Although the article does not readily lend 

 itself to abstraction, an idea of it may be gathered from the following 

 account. He considers the question under the influence of (1) direct 

 light ; (2) oblique light. With direct light the normal image is given 

 by an equation : 



M2= (^T{ i + 2/i [ cosY + 2c °4 cos ^]r- 



This equation takes slightly different forms when applied to oblique 

 light and to some of the points specially considered. His object, of 

 course, is to show that theory and observation agree. In the course 

 of the article he discusses, — normal image, hexagonal formation, ideal 

 image, depth of image, quarter-phase image, lozenge-formation, chequer- 

 formation, photomicrography. He also gives details of some experi- 

 mental ratifications. 



Behrens, H.— Anleitung zur mikrochemischen Analyse. (Introduction to Micro- 

 chen ical Analysis.) 



TSccond edition of this important work.] 



Hamburg (L. Voss), 8vo, 242 pp.. 96 figs, 



Laboratorium et Museum. 



[A new monthly scientific journal, with articles in English. German, and 

 French.] English agents, Sampson Low. Marston & Co. 



B. Technique.! 

 (1) Collecting- Objects, including- Culture Processes. 



Apparatus for Spore-sowing. §— Herr F. Noll describes the following 

 apparatus (fig. 61), which he found suitable for the regular distribution 

 of spores over a culture-surface. It consists of a wire gauze tube z, 

 which is fitted at its lower end into a hole in a circular piece of cork K. 

 Eound the rim of the cork is fastened a roll of paraffined paper p, the 

 same height as the wire gauze. The interspace is filled with calcium 

 chloride. The upper end of the apparatus is closed with a cork K, 

 having a hook N and a wire to which a piece of the plant with sporanges 

 s is attached. 



The culture medium is composed of a level layer of sterilised garden 

 earth, which is damped and placed iu a plate. The apparatus is sus- 

 pended within a bell-jar, and the latter inverted over the culture layer. 



* Zeitschr. f. Tnstrumentenk., 1899, pp. 325-35. 



t Cf. op. cit., 1898, pp. 301-17; also this Journal. 1899, p. 94. 



j This subdivision contains (1) CoHecting Objects, including Culture Pro- 

 cesses ; (2) Preparing Objects ; (3) Cutting, including Imbedding and Microtomes ; 

 (4) Staining and Injecting; (5) Mounting, including slides, preservative fluids, &c. ; 

 (6) Miscellaneous. ' § Flora, Ixxxvi. (1899) pp. 386-7 (1 fig.). 



