HARDWICKE'S SCIENCE-GOSSIP. 



49 



ON MICROSCOPICAL DRAWING 



By W. T. SUFFOLK, F.R.M.S. 



HE article by 

 E, J, D. in the 

 January number 

 of Science-Gos- 

 sip calls attention 

 to a point mucli 

 neglected, not- 

 withstanding the 

 pains taken by 

 writers on the 

 microscope t o 

 enforce the value 

 of observations be- 

 ing accompanied 

 with drawings. 



I entirely agree 

 witli E. J. D. as 

 to the extreme 

 beauty of highly- 

 finished micro- 

 scopical drawings ; 

 groups of marine and pond life make admirable 

 pictures, and furnish infinite varieties of beautiful 

 form and colour. 



A few additional hints may be acceptable to your 

 readers. 



I dispense entirely with the camera-lucida and all 

 instruments of a similar nature, and substitute a 

 grating ruled in squares placed over the diaphragm 

 of the eye-piece. I find it better to have the lines 

 ruled on a double-convex lens of shallow curvature, 

 as the interference with the definition is considerably 

 less than when a glass with plane surfaces is used : 

 with this arrangement I have seen Podura-markings 

 well shown with a \ objective. When the bino- 

 cular is required, a lens without ruling, but of similar 

 curves, should be placed in the other eye-piece to 

 equalise the magnifying power in each field. 

 A convenient distance for the lines forming the 

 squares is ^L inch, this gives a field not too much 

 crowded with squares, and on the other hand the 

 divisions are not too large to render the setting out 

 of the outline inexact. The drawing is made on 

 ruled paper, the squares being of a size suitable to 

 the intended size of the design, just as in the well- 

 No. 207.— March 1882. 



known draughtsman's process of enlarging and re- 

 ducing by squares. A drawing of any size, from a 

 small sheet to a large lecture diagram, can be made 

 directly from the microscope. 



The process also possesses the additional advantage 

 of requiring no change in the position of the micro- 

 scope, as is the case with the camera-lucida, and can 

 be used for a long time without any of the strain upon 

 the eye inseparable from the use of instruments, where 

 the image and pencil point are viewed through the 

 divided pupil of the eye. 



When measurements are required, the value of the 

 side of one or more squares can be determined with 

 the stage micrometer, and from data so obtained a 

 scale can be constructed on the drawing. 



With regard to materials I must take exception to 

 the use oi flake tuhitc for compounding body colours, 

 as in water all pigments made of carljonate of lead 

 rapidly become blackened. Chinese white, a prepara- 

 tion of oxide of zinc, should alone be used for this 

 purpose. 



The following list of colours contained in my own 

 box may prove useful: — Aureolin,* Yellow Ochre, 

 Lemon Yellow, Cadmium Yellow, Vermilion, Purple 

 Madder, Raw Sienna, Burnt Sienna, Rose Madder, 

 Light Red, Brown Madder, Cobalt, French Blue, In- 

 digo,! Vandyke Brown, Blue Black, Sepia, Viridian.+ 



In addition to the colours in cakes, a few that are 

 likely to be used in large quantities should be obtained 

 in tubes ; where thick painting is required, this form 

 of colour is particularly useful. 



The Chinese white should be kept in a bottle with 

 a greased stopper ; in tubes it soon hardens and 

 becomes unfit for use ; it should be worked with the 

 palette-knife and a little water to the consistency 

 required. 



Avoid the use of crimson and purple lakes, 



* Aureolin, a transparent pure yellow, quite permanent, and 

 an excellent substitute for gamboge, as, being without gloss, it 

 can be employed in skies and distances. 



t Indigo is only very slowly acted upon by light, and may be 

 considered permanent in the diffused light of an ordinary- 

 room ; avoid mixing with Indian red, which speedily destroys it. 



X A transparent oxide of chromium, perfectly permanent, of 

 great use both by itself and in compounding other greens ; the 

 opaque oxide of chromium may also be found useful ; both are 

 e.xtremely permanent colours. 



