INVERTEBRATA, CRYPTOGAMIA, MICROSCOPY, ETC. 499 



Arranged Diatoms for Test Slides. — Diatoms arranged in stars 

 and other patterns have hitherto been regarded as beneath the notice 

 of right-thinking mici'oscopists. Recently it has been j^ointed out * 

 that slides with six or eight diatoms arranged radially from a common 

 centre will be found useful as test objects to those whose Microscopes 

 have not a rotating stage, saving much time in manipulation, as one 

 or other of the si)ecimens will be sure to be in the position required 

 for resolution with reference to the direction of the illumination. 



Preparations of Crystals for the Polariscope-t — After pre- 

 paring crystals, dry, in Canada balsam, and in castor oil, it occurred 

 to Mr. M. A. Veeder to attemjjt to preserve them in their own mother- 

 liquor. To do this, paint on a slide a thin ring of gold size, whose 

 entire diameter shall equal that of the cover-glass. The edges of the 

 ring may be made smooth and true by holding the flat edge of a small 

 chisel against them, wliilst the turntable is whirled. As soon as the 

 ring is finished heat it over the flame of a lamp until it become brown. 

 Put into a test tube a little salyciue, tartaric acid, prussiate of potash, 

 or other substance adapted for examination with the polariscope, add 

 water and apply heat until the solution is of such strength that 

 crystals will form in it only when quite cold. Coat the ring, already 

 hardened, with a little fresh size, and likewise the edge of the cover- 

 glass. Put the slide and cover-glass thus prepared on the hot plate 

 for a few minutes and then pour a few drops of the boiling solution 

 from the test tube into the coll and apply the cover-glass immediately, 

 pressing it d.^wn gently with a dry cloth which will absorb the super- 

 fluous liquid. Toucli the edge of the cover-glass with gold size and 

 then transfer to the turntable and finish. If the above directions 

 hftve been followed correctly the cell will contain a clear liquid 

 which begins to deposit crystals as it cools. Without the aid of the 

 polariscope it is of interest, but with that accessory the spectacle 

 presented is exceedingly beautiful. After standing for some time, the 

 crystals appear to lose their sharpness and perfection of form. They 

 may be restored by a fresh application of heat sufficient to cause 

 them to dissolve and enter upon new forms of combination. 



It sliould be noted that the quantity and strength of the solution 

 employed will modify the results obtained, also agitation of the fluid 

 whilst evaporating will in some instances introduce crystals of au 

 entirely different form from those obtained when it is permitted to 

 remain undisturbed. 



Preparation of Thin Rock Sections in the Field.* — IMr. A. A. 

 Julion thinks that when a party who may bo exploring in porti«ms 

 of country where the more refined a])paratus for section grinding and 

 preparing cannot be procured, or whoi-e one is obliged tt) travel by 

 mule train, where but little luggage can be transported, tlie following 

 will answer the purpose very well, viz. a tin ln>x about 2^ X 5 inches, 

 containing a small box of flour emery (or, as a substitute, garnet may 



* • En-,']. Mcch.,' xxxi. (1SS(») p. ISl. 



t 'Am. Xiit.,' xiv. (ISSO) p. 1 k;. 



X 'Am. Joiirn. Micr.,' iv. (Ih7!t) p. 'SM. 



