372 SUMMARY OF CURRENT RESEARCHES RELATING TO 



be standardised by making test exposures on the make of plate to be 

 used, with and without them. Those who wish to read the method in 

 more detail may refer to the full report to be found in the Transactions 

 of the Royal Photographic Society for January 1909. 



(6) Miscellaneous. 



Refractive Index of Canada Balsam.* — The refractive index of 

 Canada balsam, says W. T. Schaller, as it occurs in the thin sections 

 made for the U.S. Geological Survey, was determined on the request of 

 F. C Calkins, who had found f that the index, or n, was not absolutely 

 constant, but varied between two extremes. By the examination of 300 

 slides, he found n to reach and even slightly exceed w of quartz (1 ■ 544), 

 though n was found greater than 1*544 only in the proportion of one 

 slide in a hundred. The excess was very small and the balsam was de- 

 cidedly yellow. The lowest value found by him was about 1 ' 535 ± ■ 002. 



The value of n for sodium light was determined on an Abbe-Zeiss. 

 refractometer by total reflection on three kinds of slides, which were 

 (1) not cooked as much as usual, (2) cooked as ordinarily done, and (3) 

 over-cooked. The differences found between (1) and (2) are very slight, 

 and, in fact, the individual values show almost as much variation as 

 between the different groups. The values obtained are : 



(l) (2) 



(1-539 (1-536 



» = {1*538 ?' = {l*538 » = 



(1-539 (1-539 



The average values are for (1), 1*5387 ; for (2), 1*5377 ; for (3), 

 1*5412, or, as the average of all, 1*5395, which is almost identical with 

 the value (1*5393) given by Becker | in 1898. A determination of n 

 in a slide six years old gave the value 1 * 5390. These values show that, 

 in general, n lies very close to 1*539, and that this value may well be 

 used in a study of a thin section, while the actual possible variation was 

 found by Calkins to be from 1 * 535 to 1 * 545, though the extreme values 

 are but seldom reached. The uncooked liquid balsam has a refractive 

 index of 1*524, which, after cooking, rises to 1*54. The older a slide, 

 the higher the index of the balsam becomes, which after a time, especially 

 if the air has access, reaches towards the highest value, or 1*545. 



B. Technique.§ 

 tl) Collecting- Objects, including- Culture Processes. 



Solmedia.— At the meeting of the Society held April 20, F. R. 

 Chopping, assistant in the Clinical Laboratory at the Westminster 



* Amer. Journ. Sci., xxix. (1910) p. 324. 



t Science, xxx. (1909) p. 973. 



J Amer. Journ. Sci., v. No. 4, p. 349. 



5 This subdivision contains (1) Collecting Objects, including Culture Pro- 

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

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

 (6) Miscellaneous. 



