WITH THE MICROSCOPE. 29 



If the engraving is to be a. fac-simile of the drawing with the 

 different parts on corresponding sides, it is necessary, in the first 

 place, to copy the picture with ordinary tracing paper, and invert 

 the tracing upon the retransfer paper on the wood block, as the 

 impressions are of course always reversed ; or a reverse may be 

 obtained by copying the image of the drawing reflected from a look- 

 ing-glass. Specimens of wood engraving are seen in many of the 

 plates in this volume. 



4 1 ?. Pencils. Many excellent lead pencils are now made. Those 

 known as Faber's, is. gd. a-dozen, are among the best and 

 cheapest HH's or HHH's are sufficiently hard for ordinary drawing 

 on paper, but for drawing on wood a four or five H is to be 

 preferred. Drawings of microscopic objects may also be made 

 with India ink or sepia, a fine brush or pen being used. If the 

 observer draws on wood, he will save time by representing the 

 shading as a //;;/, and different kinds of shading may be indicated 

 by different colours applied with a camel's hair brush in the usual 

 way. 



48. Tracing Paper is a very transparent paper, obtained by soak- 

 ing tissue paper in some oily material, and allowing it to dry. Re- 

 tracing paper consists of tracing paper, upon one side of which a fine 

 red, blue, or black powder has been rubbed, which adheres to the 

 paper pretty firmly, but which, at the same time, will readily adhere 

 to another surface if firm pressure be applied. 



49. Wood Blocks are prepared by rubbing a little dry carbonate 

 of lead and brick dust moistened with water upon the surface, and 

 allowing a very little to dry on. In this way a smooth white surface 

 is obtained, admirably adapted for receiving the most delicate draw- 

 ing. It is well to moisten the white lead with a little very weak gum 

 water, which makes it adhere firmly to the surface and gives a 

 very smooth face. If the face of the block is not smooth, it may be 

 rubbed with the hand or a piece of hard paper or wash leather. Every 

 observer should learn to draw on the wood block himself. There 

 is no great difficulty, and a little practice will enable him to draw as 

 well on wood as on card-board. 



50. Of obtaining Lithographs of Microscopical Drawings. I 

 think it desirable to give a few directions for drawing on stone, as I 

 believe there are many observers who would willingly give up the 

 necessary time required to place their work on the stone, who could 

 not afford to employ a lithographic artist. I made many drawings in 

 this manner some years ago (see the earlier numbers of my ' Archives') 

 and with the help of a boy, who could at first draw but little, have 

 been able to publish numerous drawings, which are very accu- 



