New Finder for the Microscope. By Joseph M. Coon. 275 



can be referred to, or parts repeated without removing the slide from 

 the stage, a matter of very great convenience when using immer- 

 sion objectives — in fact, it is easier to find objects with it than by 

 the mechanical stage, because the light available is often insufficient 

 or inconveniently placed for reading stage divisions. 



The actual design of finder may vary, but it essentially consists 

 of a means of attaching to the Microscope a pointer with universal 

 movement (fig 40). The finder exhibited this evening has a plain 

 clamp with milled-head screw for fastening to stage ; on clamp is 

 mounted a pointer holder with horizontal motion, a screw through 

 which holds the pointer ; this pointer has a vertical and sliding 

 motion, and is clamped by the screw when adjusted. 



In conjunction with the finder a registering label is used. This 

 may be ruled in many ways, but the author has found the ruling 

 shown (fig. 41) very suitable and simple. 



The vertical columns of large squares are indicated by capital 

 letters, the horizontal lines of large squares 

 by numbers on the left hand ; each square 

 is divided into four smaller squares, indi- 

 cated by small letters, a, b, c, d, and each 

 small square into four triangles by diagonal 

 lines. The side of each small square equals 

 1 • 25 mm. ; by the triangles it is quite easy 

 to indicate the position of the pointer to ^ of 

 this, or say 0*25 mm., or t ^q of an inch. 

 The field of a Zeiss 2 mm. N.A. 1-40 ob- 

 jective is given as ■ 25 mm. diameter. 

 It is quite evident, therefore, that high 



powers can be used with the finder. The author finds no diffi- 

 culty in using a £ Beck ; of course care must be used, and, with 

 high powers, the quiet of a laboratory is most helpful. The label, 

 besides its ruling, has two marks, one called the registering mark, 

 and the other the focusing mark.* 



To register a slide, the objective is focused on the focusing 

 mark, and the pointer adjusted to registering mark. 



Tiie slide is then searched and parts registered. (For immersion 

 lenses the focusing mark is best placed on the vacant space of cover- 

 glass.) To register : the capital letter over large square, number 

 opposite, small square under by its small letter, and position in 

 triangle by a dot, thus \^/ • A complete record might be — 

 Ali ' 



Fig. 41. — A, Focusing mark. 

 B, Registering mark. 



', and would indicate' that the part is in field when 

 the pointer is under A, opposite 1, over a, and in centre of upper 

 triangle. 



* The author finds that it is really best, always to place the focusing mark on 

 clear space of cover-glass, as it is easier found ; a very fine dot or cross of Indian 

 ink or gentian-violet in Holies glue is very durable and suitable. 



T 2 



