108 SUMMARY OF CURRENT RESEARCHES RELATING TO 



the Imperial Standard yard are sharp-edged, but contain the equivalent 

 of 40 interference bands of red light in their thickness, and the Benoit 

 defining lines of the platinum-iridium copy made in 1902 are not only 

 very ragged edged but contain 15 interference bands in their thickness. 

 By the help of J. H. Grayson, of Melbourne, it has been found that 

 wonderfully satisfactory rulings on the scale of 40,000 to the inch can be 

 made on polished speculum metal covered with a thin cover-glass. Now 

 the forty-thousandth of an inch is a single wave-length of red light (for 

 Ha = 3^tttt i n -5 an( l Cd red = ^^j^ in.), so that the interval between 

 any adjacent pair of these lines is equivalent to only two interference 

 bands. The thickness of each line, which is absolutely sharp-edged, is 

 less than a single interference band. The author has therefore devised 

 a " Tutton location signal," consisting of five such parallel lines spaced 

 -nnjoiy m - apart, with a pair of strong "finder" lines outside them 

 and parallel to them, and another pair of similar finder lines, per- 

 pendicularly transverse to them, to indicate a central part of the lines 

 lines for use. The central line of the five fine Grayson rulings is the 

 defining line. 



Pocklington, H. C. — The Aberrations of a Symmetrical Optical Instrument. 

 [A mathematical treatment on Lord Rayleigh's article on Hamilton's 

 Principle and the Fine Aberrations of von Seidel.] 



Proc. Boy. Soc, Series A, lxxxiii. (1909) pp. 99-106. 



(6) Miscellaneous. 



Observations on Mammalian Blood with Dark Field Illumina- 

 tion.* — H. Crawley finds that the dark field illumination is a sine qua 

 non for examining fresh blood. The apparatus used consisted of a 

 substage condenser, arc lamp, and rheostat for cutting down the current 

 to 4 amperes. It was found to be important that the slides used should 

 not exceed 1 mm. in thickness. The work was done with a -jV in. 

 achromatic immersion lens stopped down with a hard rubber funnel and 

 a No. 12 compensating eye-piece, though equally good pictures were 

 obtained with a No. 18 eye-piece. The blood studied was that of the 

 cow, sheep, rabbit, guinea-pig, white rat, and man. The blood of sheep 

 and cow was drawn from the jugular vein, defibrinated and preserved in 

 cultured tubes. The media used were bouillon, citrated salt solution, or 

 simple salt solution. Citrated salt solution appears to have a destructive 

 influence on the blood cells after a certain time. It was also noted that 

 the dark field illumination acted injuriously on living cells, and that 

 trypanosomes perished very quickly under its influence. The phenomena 

 observed are treated under the following heads : (1) Blood dust ; (2) 

 beaded threads ; (3) flagellated erythrocytes and free flagella ; (4) bodies 

 showing pseudopodia ; (5) erythrocytes ; (6) leucocytes ; (7) blood 

 plates. 



Quekett Microscopical Club. — The 459th Ordinary Meeting of the 

 Club was held on Tuesday, October 2G, 1909, the President, Prof. E. A. 

 Minchin, M.A., F.Z.S., in the Chair. Mr. W. Wesche, F.R.M.S., com- 

 municated two papers, one " The Life-history of the Tachinid Fly, 

 Phorocera serriventris Rondani," and a " Note on a Quick Method of 



* U.S. Dep. Agric, Bull. 119, Washington, 1909, pp. 5-15 (1 fig.). 



