ZOOLOGY AND BOTANY, MIOEOSCOPY, ETC. 395 



MICROSCOPY. 

 A. Instruments, Accessories, etc.* 

 (3) Illuminating' and other Apparatus. 



Modified Safety-razor Blade-holder for Temperature Control. — 

 T. H. GooDSPEED {Botanical Gazette, 191<s, 2, 176-7, 1 fig:.). The 

 necessity of keeping the knife cool in ribbon section-cutting has led in 

 the University of California Laboratory to a simple modification of the 

 usual type of safety-razor blade-holder. The original holder made by 

 Strickler has been found the most desirable type of a number at present 

 on the market. To such a holder a small brass tube is longitudinally 

 attached. This tube has a bore of 4 mm., and is soldered to the outer 

 leaf of the holder, thus in no way interfering with the separation of the 

 leaves when the safety-razor blade is to be inserted. The tube is 

 extended approximately 6 mm. beyond the holder proper at either end to 

 allow the attaching of small rubber tubes. For class use where very 

 thin sections are not ordinarily required, it has been found that the 

 temperature of the knife in such a holder is sufficiently low if tap-water 

 is allowed to flow through the tube. A very short time is required for 

 the temperature of the water to be communicated to the knife. A 

 cooling-cell, such as Land's or Gardner's, also regulated with tap-water, 

 may be employed in addition, but its use in most cases is superfluous. 

 Where sections from soft or medium paraffin under 5 /a are required the 

 modified safety-razor blade-holder and the cooling-cell are attached to 

 Gardner's apparatus, with the buckets filled with ice-water. Under 

 such conditions sections 2 ^ thick have been cut very sflccessfully from 

 a paraffin melting at 53° C. A. N. D. 



Scattering of Light by Dust-free Air, with Artificial Reproduction 

 of the Blue Sky. — Hon. R. J. Strutt, F.R.S. {Royal Societtj Proceed- 

 ings, June 1918, 94, 453-9). It is now recognized that the blue 

 colour of the sky on clear days and at considerable altitudes can be 

 accounted for by the scattering of light by the molecules of air, without 

 postulating suspended particles of foreign matter, such as were thought 

 necessary by earlier writers. The laboratory method described of 

 demonstrating this is in principle a modification of the ultra-microscope 

 of Siedentopf, which again is founded on the observations of Tyndall. 



* This subdivision contains (1) Stands ; (2) Eye-pieces and Objectives ; (3) 

 Illuminating and other Apparatus ; (4) Photomicrography ; (5) Microscopical 

 Optics and Manipulation ; (6) Miscellaneous. 



