ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



357 



to revolve rapidly a quick adjustment, suitable for low powers, is ob- 

 tained, while the large milled head is available for delicate adjustment 

 and high powers. 



Beck's Micrometer Microscope. — This instrument 

 (fig. 71) is intended for the accurate measurement of 

 either opaque or transparent objects. The eye-piece 

 has cross lines, and the whole Microscope is traversed 

 across the object by means of a fine micrometer screw. 

 On the upper portion of the stand is a scale repre- 

 senting the number of turns of the screw, whilst the 

 drum of the milled head records to T ^th of a milli- 

 metre. The Microscope has a rack-and-pinion focus- 

 sing motion, a graduated draw-tube, and carries the 

 standard Royal Microscopical Society screw. 



The stand is so made that the entire portion carrying the Microscope 

 and micrometer screw may be removed, and attached in a horizontal 

 position. A telescope object-glass may then be used in place of the 



Fig. 70. 



Fig. 71. 



