660 SUMMABY OF CURRENT RESEARCHES RELATING TO 



repeated measurements gives the angle to about 2 minutes, corresponding 

 to units in the third place of decimals. 



In using the instrument the objective is replaced by Bertrand's lens 

 for convergent light, or the objectives or 1 of Nachet may be employed. 



Fig. 186. 



As regards the liquid, there are many objections to the use of carbon 

 disulphide, and M. Thoulet recommends biniodide of mercury and potassium 

 as more convenient than either naphthaline monobromide or solution of 

 sulphur or phosphorus in carbon disulphide. In any case it will not be 

 possible to determine an index of refraction which is greater than 1 • 7. 



A Microscopic Advantage. 



["By inverting a 1/4 in. objective over the eye-piece of the Microscope an 

 arrangement is produced which immediately gives the images in their proper 

 position, and not upside down, as without it. This is a considerable advantage, 

 because it enables a worker to go straight to the object without the mistakes 

 which so frequently occur with beginners."] 



Soientif. Enquirer, II. (1887) pp. 106-7. 

 Hallsten, K. — Ein Compressorium fiir microscopische Zwecke. (A compressorium 

 for microscopical purposes.) 



[A brass tube surrounding the objective, at the lower end of which a cover-glas8 

 is cemented with shellac. It can be used as a compressorium, and also to 

 prevent the dimming of high powers with water vapour when observing delicate 

 transparent objects in the living condition on the hot stage.] 



Zeitschr. f. Biol., XXII. (1886) pp. 404-7 (1 fig.). 

 Ketchum's (J.) Portable Oxy-calcium Lamp. 



[" When packed occupied a case only 13 in. long by 6 in. square. The oxygen 

 cylinder was 3 x 12 in. long, and contained four hours' supply. The illumina- 

 tion was very fine."] 



Amer. Mon. Micr. Journ., VIII. (1887) p. 97. 

 Laboratory Notes. 



[Usefulness of a simple and inexpensive eye-piece micrometer as a part of the 

 outfit of each Microscope in the laboratory. Culture-cells made of vulcanite 

 rings.] 



Amer. Natural., XXI. (1887) pp. 477-9. 

 N., W. J.— The Two Mirrors. No. VI. Sci.-Gossip, 1887, pp. 75-6 (1 fig.). 



