ON MICROSCOPICAL DRAWING AND PAINTING. 167 



the interior for the drawing and the lines for back- 

 ing with indian ink these discs should be prepared 

 before the work is commenced, and the importance 

 of this arrangement will be shown hereafter. 



The help derived from the caraera-lucida is strictly 

 limited, it cannot be employed beyond a certain 

 point, no elaboration can be effected by its pro- 

 longed use, it should be discarded the moment its 

 legitimate purpose of marking points and positions 

 is achieved ; those experienced in its employment 

 always feel a sensible physical relief, and " breathe 

 again " when it is set aside to settle down to the 

 earnest work of direct vision. The application of 

 the camera-lucida to the instrument is sufficiently 

 familiar ; the microscope, if a binocular instrument, 

 having been rendered monocular by withdrawing 

 the prism, the camera-lucida is slipped over the A 

 eye-piece which should always be used (higher 

 eye-pieces expand the field beyond the fair range 

 of the instrument). The object being clamped, the 

 microscope is depressed into a true horizontal posi- 

 tion (if not, a distorted picture would result), and 

 the lights adjusted ; the distance from the object to 

 the eye-piece should be nearly equivalent (if any- 

 thing a little more) to the reach from the eye-piece 

 to the paper. With a microscope standing ten or 

 twelve inches high (a Ross No. 1) this condition 

 would reveal the phantom of the object, outside or 

 about filling a circle of the dimensions given on the 

 drawing block ; if any difference of over, or within, 

 lapping appear, it may be remedied by raising or 

 otherwise adjusting either the paper or the micro- 

 scope so as to obtain a perfect coincidence of the 

 vision and the circle ; the importance of a measured 



