CH. II] 



LIGHTING AND FOCUSING 



73 



fatigue incident upon using the microscope at first is due partly at 

 least to the constant effort on the part of the observer to remedy 

 the defects of focusing the microscope by accommodation of the 

 eyes. This should be avoided and the fine adjustment of the micro- 

 scope used instead of the muscles of accommodation. With a micro- 

 scope of the best quality, and suitable light — that is light which is 

 steady and not so bright as to dazzle the eyes nor so dim as to strain 

 them in determining details— microscopic work should improve 

 rather than injure the sight. 



Fig. 68. Laboratory 

 with adjustable stool. 



Table 



§ 128. Position and Char- 

 acter of the Work Table. — 



The work-table should be 

 very firm and large (60 x 120 

 cm.; 24 x 48 in.), so that the 

 necessary apparatus and ma- 

 terial for work may not be 

 too crowded. The table 

 should also be of the right 

 height to make work by it 

 comfortable. An adjustable 

 stool, something like a piano 

 stool is convenient, then one 

 may vary the height corres- 

 ponding to the necessities of special cases. It is a great advantage 

 to sit facing the window if daylight is used, then the hands do not 

 constantly interfere with the illumination. To avoid the discomfort 

 of facing the light a screen like that shown here and in Fig. 66 is 

 very useful (see also under lighting, § 71). 



LABORATORY TABLE. 



TESTING THE MICROSCOPE 



§ 129. Testing the Microscope.— To be of real value this must be accom- 

 plished, by a person with both theoretical and practical knowledge, and also 

 with an unprejudiced mind. Such a person is not common, and when found 

 does not show over anxiety to pass judgement. Those most ready to offer ad- 

 vice should as a rule be avoided, for in most cases they simply "have an ax to 

 grind," and are sure to commend only those instruments that conform to the 

 " fad" of the day. From the writer's experience it seems safe to say that the 



