J. M. COON ON A NEW FINDER FOR THE MICROSCOPE. 329 



t Jq in. As the field of the Zeiss 2-mm. N. A. 1-40 apochro- 

 matic objective is given as 25 mm. in diameter, it is evident that 

 the finder is available for use with high powers. The author finds 

 no difficulty in using a Beck y^th-in. Of course, care is needful, 

 and the quiet of a laboratory most helpful. The slide has also two 

 marks, one called the focussing mark, the other the registering 

 mark. 



To register a slide, the objective is focussed on the focussing 

 mark, and the pointer adjusted to the registering mark. Both 

 may be on the label, or, better still, the focussing mark may 

 be placed on a vacant space on the cover-glass — in fact, this is 

 necessary for use with high powers. The slide is then searched 

 and parts registered by recording where the pointer indicates on 

 the label, by entering the capital letter over the large square, the 

 number opposite the horizontal square, the small square by its 

 small letter, and the position of a triangle by a dot, thus \7. A 

 complete record might be A, 1, a, \7, meaning that the point re- 

 ferred to is in the field when the pointer is under A, opposite 1, 

 over small square a, and over the centre of the upper 

 triangle. 



To find an object, focus on the focussing mark, fix the pointer 

 over the registering mark, move the slide until the pointer stands 

 over that part of the label indicated by the register, when the 

 object should be in the field of the objective. 



The foregoing refers to microscopes with mechanical stages, or 

 with a parallel sliding bar, the slide being kept in contact with 

 the bar and a stop. 



If the instrument has a plain stage with clips, the pointer has 

 two points or other equivalent means of adjusting parallel to the 

 ruling on the label : the right-hand point is set to the registering 

 mark, and the left-hand point on a line continuing from it 

 horizontally, the objective being focussed as before. The only 



