358 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Microscope object-glass, and focussecl by means of tbe draw-tube. In 

 this way the instrument may be used for readings at a distance. 



Albrecht's Microscope for Measuring Plant-Growth.*— The modern 

 form of this instrument is shown in fig. 72. The tripod base is carried 

 on levelling screws s, and the adjustment of the Microscope-tube is 

 controlled by the level L. The sleeve H forms a part of the heavy 

 base and contains a pillar S, which is raised or depressed by the screw 



Fig. 72. 



v, which thus acts as a coarse adjustment. The finer vertical adjustment 

 is effected by the micrometer screw M, an indicator Z serving, in con- 

 junction with the graduated plate P, to read off the movement. The 

 screw 6 regulates the motion and the direction of the tube-length, and 

 another screw c imparts a slight lateral movement of the entire upper 

 part. Dr. Zimmermann considers that an arrangement for adding rota- 

 tion about a horizontal axis would be a desirable addition. The optical 

 parts are made by Seibert, of Wetzlar. 



Pye's Reading Microscope.— Messrs. W. G. Pye and Co.'s reading 

 Microscope (fig. 73) is designed on the geometric slide principle. A 

 steel cylinder, to which is clamped, in any position, the Microscope 

 arm, and forms the carriage, works in a pair of V's cut in the uprights 

 of tbe base. These V's are parallel to the top plane edge of the base, 



* Zimmermann, Das Mikroskop, 1895, p. 106, fig. 77. 



