ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 701 



forms can be brought out, as according to their hardness each form 

 will become more or less transparent, since the softest parts will 

 be worn faster, and hence be finally thinner and more trans- 

 parent than the more resisting forms. Sections parallel to the bed- 

 ding are made without difficulty; not so sections at right angle. 

 Much precaution is to be exerted with these. Cut the raw plate with 

 a steel saw 4 mm. thick, 15 mm. square. Make a plane cut as usually 

 in rock sections, but using only the finest emery (polishing emery) or 

 precipitated carbonate of calcium. Then rub the surface gently in all 

 directions with a cork plate (perfectly soft and no grains) 10 mm. 

 square, and moistened with a drop of glycerine. This treatment pro- 

 duces the relief. Frequent examinations must be made under the 

 Microscope, to observe the point where the desired transparency has 

 been reached (not less than 0-01 mm.). In some cases, as for 

 trichites and grammites, it is best to warm the raw plate and saturate 

 it with a mixture of wax and paraf&n. When attaching the plate to 

 the support, it should neither be heated too long with the balsam nor 

 too short a time, the first excess causing the plate to warp, crack, and 

 inducing a partial alteration of some of the coal constituents ; too 

 little boiling causes the plate to detach itself from the support during 

 the process of grinding. Chemical treatment with acids or alkalies is 

 not advisable. 



A microscopic image of the condition of things in a coal section 

 may be obtained by closely inspecting a sharp cut through a com- 

 pressed ball of hay. Here the innumerable plant individuals are cut 

 in every direction. The different sections of the same plant have 

 often so little in common that an identification of the species is 

 extremely difficult. This is true of a microscopic coal section ; and 

 only the comparison of very many specimens will establish the common 

 characters of the forms. Professor Eeinsch's conclusions, to which 

 we referred at page 836 of vol. iii., are drawn from 1200 perfect 

 sections. 



Simple Method of making Rock Sections.* — The process of 

 reducing stone and other hard substances to thin sections for micro- 

 scopical examination by the methods usually employed by amateurs is, 

 Mr. W. C. Brittan considers, both tedious and laborious, requiring a 

 great amount of patience and some ingenuity, with a commonly un- 

 satisfactory result ; and he therefore gives some suggestions from his 

 own experience that are very efficacious with all substances not too 

 hard to be reduced by grinding with emery. 



Take a piece of plate glass — 3 x 4 inches is a very convenient size 

 — set in a block of wood ; a circular piece of inch-thick pine, with 

 three screw-heads placed triangularly underneath, will be found to 

 give it great solidity upon the table, a qualification very desirable in 

 doiug delicate work. Upon this piece of glass, with emery and 

 water, grind one side of a glass slip to an evenly ground surface. 

 Next, take the stone or other substance from which a section is to be 

 made, and in the same way grind down one side of it to a suitable face. 



* Amer. Joum. Micr., vi. (1881) p. 12. 

 Ser. 2.— Vol. I. 3 A 



