ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



581 



second movable thread, the whole ocular micrometer is moved by the two 

 screws a and e (fig. 110) ; the arrangement being contained in the box 

 which is clearly shown in the lower part of fig. 109. In use the object 



Fig. 109. 



is^brought exactly into the midst of the field, and by means of the two 

 screws* a and e the first division of the scale is brought over one 'of the 



Ftg. lio. 



boundaries of the object to be measured ; the other movable thread is 

 then brought into position by means of a and 6 ; and the whole is raised 



and the reading taken. 



Strehl, K. — Theorie des Zweilinsigen Objectivs. (Theory of the Two-Lensed 

 Objective.) Zeitsohr.f. Imtrumentk., XXII. (1901) p. 10. 



Oct. 16th. 1901 2 it 



