166 



reading, these will be required in order to see the 

 pencil point clearly. 



The pencil point should be well sharpened in 

 order to closely follow the minute detail. 



The drawing board should be at right angles to 

 the axial portion of the projected image, otherwise 

 there will be an elongated picture. 



The relative illumination of field and paper 

 varies with magnifying power and distance of eye- 

 piece from paper, but should be made as nearly 

 alike as possible. In low powers the light from 

 the objective is stronger than that from the paper 

 and should be modified, in the simple and Wollas- 

 ton forms by using the plane mirror or by cover- 

 ing it with white tissue paper, and in the Abbe 

 form by the use of dark tinted glass, which is pro- 

 vided with the apparatus. In the higher powers 

 the paper is brighter in which case it should be 

 shaded by a screen placed between it and the source 

 of light, or a substage condenser should be used 

 to give increased illumination. 



Special instructions with reference to the use of 

 the simple and Wollaston forms are as follows : 



Focus the objective upon the object ; then in- 

 cline the microscope, preferably to the horizontal 

 position ; raise the microscope by underlaying 

 with a block or books. The size of drawing may 

 be varied by change of eyepiece or objective, but 

 only to a limited extent ; or by varying the dis~ 



