48 



THE MICROSCOPIST. 



four of its toes, and the web is spread out over the large hole 

 by fastening the ends of the thread through the small holes 

 in the plate. 



Fig. 18. 



The Stage Micrometer consists of a slip of glass, pearl, &c., 

 having a line finely divided into parts of an inch, &c. To 

 obtain with this the power of a compound microscope, compare 

 the divisions seen with one eye through the instrument, with 

 a rule held ten inches off, and looked at with the other eye. 

 Suppose, for instance, the micrometer be divided into -j-J^ths 

 of an inch, and one of these divisions covers an inch of the 

 rule seen with the other eye, the magnifying power of the 

 instrument is 100 diameters. If it should cover five inches, 

 it is magnified 500 diameters. By sketching the object by 

 means of the camera, and then putting in its place a stage 

 micrometer, and marking the divisions over the sketch, they 

 can again be subdivided, and so the measure of an object 

 be accurately taken. 



