I. MICROSCOPES. 913 



3579. Large Microscope. Dr. Hartnack, Potsdam. 



These instruments are sufficiently well known, and it is not necessary to 

 bring forward their peculiarities, but the mineralogical microscope has been 

 recently constructed, and the exhibitor requests mineralogists to direct their 

 attention to it. 



3579a. ETew Dissecting Microscope with three achromatic 

 powers, support for arms, and rack focussing giving three move- 

 ments. Harvey, Reynolds, and Co. 



3 5 SO. Microscope for Dissecting, with forceps and plate 

 for dissection, and simple Microscope with rod action. 



Geneva Association Jor the Construction of Scientific In- 

 struments. 



The Geneva Association constructs three different patterns of microscopes. 

 In the simplest form the focussing movement is worked direct by the hand 

 acting upon a rod which supports the optical system, and which slides up and 

 down through a groove. The light is given by a mirror placed below the 

 stage. In the second pattern the focussing is effected by means of a rack. 

 Lastly, in the third pattern, the most complete of all, a pair of forceps 

 revolving around two rectangular supports is substituted for the plate. By 

 this means an object can be successively examined on all sides, and without 

 leaving the focus of the glass. The optical parts are the same as in the 

 preceding. 



length of vision. 



The Geneva Association supplies besides to those who require higher 

 powers achromatic lenses of short focus, giving great clearness and light. 

 An achromatic lens of 2 millimetre focus produces a magnifying- power of 125 

 times with perfect clearness. 



3558. Small Microscope, with a Cylindrical Clip for 

 Objectives. 



Geneva Association fw the Construction of Scientific In- 

 struments. 



This pattern of microscope is at once strong and simple. The system of 

 the cylindrical clip is as follows : 



The objective is not screwed into the tube, but is held bj- a spring against 

 a carefully turned bearer. To remove the objective, it is sufficient to draAv 

 it away transversely after having lowered it so as to exert a pressure in the 

 direction of the axis. The objective is more easily placed in position than 

 removed. The advantages resulting from this arrangement are : 



1. A great saving of time to the observer, changes of magnifying power 



being rapidly accomplished. 



2. The mechanical centering of the objective is better than that usually 



obtained with the screw. 



3581. Large Microscope, with Reversing Action, and 



cylindrical clips for objectives. 



Geneva Association for the Construction of Scientific In- 

 struments. 

 40075. 3 M 



