ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 107 



Journal, has been altered. Mr. Gifford's measure of A for white light, 

 viz. 0*5607 /a has been substituted for that hitherto used, viz. * 5261) //. 

 (line E). In the calculation the new metrical conversion table " for 

 same temperature" was employed. 



Resolution of Amphipleura Pellucida.* — C. Mostyn has resolved 

 the transverse striae on the Amphipleura pellucida with a water immersion 

 -j 1 ^ N.A. 1*18, by means of superstate illumination, simply obtained by 

 reflecting sunlight with the mirror turned up above the stage. The 

 author is able to obtain an " ink-black " ground by this means, and 

 observes that light from an §-in. paraffin wick is not sufficiently powerful 

 for this kind of superstage illumination. 



Ultramicroscopic Observations on the Decomposition of Sulphur 

 from Thiosulphuric acid and of Selenium from Selenic acid.j — The 

 investigations of Siedentopf and Zsigmondy with ultra-microscopical 

 particles suggested to W. Biltz that, although the measurements of 

 so-called "molecular dimensions" are somewhat beyond the limits of 

 resolution, yet the observer's methods might be usefully applied to the 

 investigation of certain cases of chemical composition and decomposition. 

 He considers that (1) the ultramicroscope draws a sharp distinction 

 between completely homogeneous (or " optically empty ") solutions and 

 those which appear turbid through a more or less fine suspension of 

 minute particles : the diagnosis of so-called colloidal solutions being 

 thereby simplified ; (2) that it lends itself to a more accurate study of 

 certain processes by which a heterogeneous medium is formed out of one 

 originally homogeneous. He has examined the decomposition of thio- 

 sulphuric acid into sulphurous acid and sulphur (H 2 S 2 3 = H 2 S0 3 -f S), 

 and the conversion of selenic and sulphurous acids into selenium and 

 sulphuric acid (H 2 Se0 3 + 2H 2 S0 3 = H,0 + Se + 2H 2 S0 4 ). Great diffi- 

 culty was experienced in freeing the reagents, especially distilled water, 

 from dust, but eventually success was attained. It was found that india- 

 rubber couplings had to be avoided owing to partial solution. Experi- 

 ments were also performed with proper mixtures of sodium thiosulphate 

 and oxalic acid. Observations were made at suitable time-intervals, and 

 several tables are given recording the growth of the particles and their 

 colour-changes. In some cases the growth seems to be continuous, in 

 others discontinuous. 



Colours in Metal Glasses and in Metallic Films.f — J. C. Maxwell 

 Garnett seeks to explain the phenomena observed by Siedentopf and 

 Zsigmondy by proving that the metal particles observed in gold glass 

 are spherical in shape when the diameters are less than 10" 5 cm. The 

 fact that such particles are spherical throws light on the manner in 

 which metals crystallise out of solution, the particles taking first a 

 spherical form under the influence of surface tension, and later, when 

 they become too large for the forces of surface tension to overcome the 



* Knowledge, i. (1904) p. 307. An interesting question arises from this note, 

 How does light of an obliquity greater than the critical angle get into the slide ? — Ed. 

 t Nachrichten Konigl. Gesell. wiss. zu Gottingen, (1904) pp. 300-10. 

 X Proc. Roy. Soc, lxxiii. (1904) pp. 443-5. 



