16 THE AMERICAN MONTHLY [Jannniy, 



suit of this process the glass has a rough surface and is no longer trans- 

 parent. It is now transferred to the " fine tool." This is made of 

 brass and has its surface as true as possible. It is compared from time 

 to time with a standard curve, in order to insure accuracy. In this 

 second grinding the abrading material is rouge (carefully calcined sul- 

 phate of iron). Finally, the lens is polished by being pressed against 

 a piece of cloth powdered with rouge and fastened to the rotating tool. 

 The glass is now loosened from its block, turned over, and the reverse 

 side of the lens ground. When this has been accomplished, the lens 

 must be cut down to the proper shape for mounting in the spectacle- 

 frame. It is placed on a leather cushion and held firmly in position by 

 a rubber-tipped arm, while a diamond glass-cutter passing around an 

 oval guide traces a shnilar oval on the glass below. The superfluous 

 glass outside of the oval is removed by steel pincers, the rough edges 

 are ground smooth on Scotch wheels and the lens is ready for mount- 

 ing. The glasses for small telescopes, microscopes, burning-glasses, 

 and the like are ground in the same fashion. — Prof. C. II. Henderson, 

 m The Popular Science MontJiy. 



Collecting Sediment for Examination. — Dr. Ruttan, of Mon- 

 treal, allows the water to stand in a large vessel for a time and then 

 syphons otl the clear water, leaving a small amount of water with the 

 sediment. This residual, well shaken, is transferred to a tube (60 x 

 100 cm.) supported by the Bunsen stand. This tube has an aperture in 

 the constricted base fitted exteriorly with a small glass cap, into which 

 the converging sides of the tube conduct the sediment. A rubber stop- 

 per with a long handle may be let down through the water and close 

 the tube just above the cap. The cap when removed contains the sedi- 

 ment and scarcely any water. The tube is graduated for i, 3, or 3 

 litres of water, and the sediment of 3 litres deposited in about 50 cc. 

 space quite ready for microscopic examination or for quantitative meas- 

 urement. 



MICROSCOPICAL MANIPULATION. 



A New Mounting Fluid. — Mr. Haly, curator of the Colombo 

 Museum. Island of Ceylon, used carbolic acid, cocoanut oil, and turpen- 

 tine, which readily mix together, to form a fluid in which objects may 

 be allowed to soak without any previous preparation and in which they 

 become very transparent. He kept the leg of a fly on a slide in a drop 

 of this fluid for ten months without alteration. No cell was made, no 

 cement employed, and an ordinary cover-glass was simply laid over 

 the object. We have written Mr. Haly, asking for the proportions 

 which he used. 



A more extensive use of cocoanut oil and carbolic acid was made for 

 a preservative fluid, and it was found to preserve the colors of various 

 animals, including those most changeable colors of fishes and of frogs 

 and of snakes, in the most beautiful manner. The mixture used for 

 that purpose consisted of cocoanut oil raised to the specific gravity of 

 10° or of 20° below proof-spirit by the addition of carbolic acid. 



Fuller data may be found in the last annual report of the Colombo 

 Museum. 



Crustacean Eyes are stained by G. H. Parker with alum cochi- 



