ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



579 



inconvenience may be experienced in using the lens owing to the neces- 

 sity of havin^ to bring the eyes close to the object under examination. 

 The focussing Microscope (tig. 105) is intended to obviate both faults, 

 as it has a magnifying power equal to about 28 diameters, and allows of 

 the eye being kept at a convenient distance from the object. The instru- 

 ment is fitted with a double action for rough and fine focussing. When 

 used, it is firmly held witli the left hand between the base-plate and the 

 nearest milled clamping ring, and the clamping ring is then loosened. 

 The tube is then held with the right hand at the fixed milled band 



Fig. 105 



Fig. 106. 



above the zero mark of the millimetric scale, and roughly focussed by 

 sliding the tube in or out of the sleeve held in the left hand; the 

 clamping ring is then tightened. The fine focus is then obtained by 

 screwing the tube in or out of the second or upper sleeve. Before this 

 can be done, the second clamping ring (situated on the ^ division out- 

 side of the tube) must be loosened. The millimetre scale on the tube, 

 in conjunction with another graduation on the upper edge of the sleeve, 

 enables one to read at a glance quantities as small as T V mm., and to 

 estimate correctly T ^ mm., so that the most 

 minute differences of distance between two objects 

 can be estimated almost down to T ^ F mm. 



Zeiss' Focussing Glass. — This apparatus is an 

 auxiliary, primarily intended for viewing trans- 

 parent objects, either for sharply focussing the 

 picture on the grouud glass screen, or for test- 

 ing negatives required for copying processes as to 

 their precision and quality. Tbe lens is sup- 

 plied in the form of mount shown in fig. 106, 

 and in three magnifying powers, viz. 6, 10, 16 

 diameters. The first and second are preferable 

 for focussing, the second and third are for the ex- 

 amination of negatives. When used, the milled 

 clamping ring is first unscrewed, and the instru- 

 ment placed upon the ground glass scre«n or nega- 

 tive; the lens is then sharply focussed by screwing the cell in or out 

 by means of its projecting upper edge. Subsequent disturbance is 

 prevented by carefully screwing the clamping ring back again. 



Kohn, R. — Versuche iiber eine Elektrochemische Mikroskopie und ihre Anwendung 

 auf Pflanzcnphysiologie. (Investigations concerning an Electrochemical Micro- 

 scopy and itd application to Plant Physiology.) 



Prag (H. Mercy Sohn), 1901, 30 pp. 



