i6 



With insular prejudice, however, the only continental 

 names mentioned are Leeuwenhoek and Lieberkuhn. 



Condensers placed so as to concentrate light upon th^ 

 object were not thought of before 1691, when Bonnanus 

 first used a condenser below the stage, so as to illuminate 

 transparent objects. Up till this time compound instru- 

 ments had to be used vertically, or else directed at the 

 sky. Looking up to the heavens for any length of time 

 through a microscope, especially Cornelius Drebell's 6ft. 

 one, must have been most tiring. 



The next notable advance in mechanism was the fine 

 adjustment screw. This can be credited to Marshall, 

 1704. Previous to fhis, Hooke's microscope rotated in 

 a screw socket, whereas Divini's and Cherubin's Worked by 

 slidijig cylinders. In some cases the object was raised 

 or lowered, to suit the focus of lens. In Marshall's 

 instrument the condenser was on the swing-out principle, 

 being fixed to a jointed arm. One bad feature was the 

 illumination by candle under the stage, which must have 

 been bad for the observer's face; almost as bad as our 

 oil lamps are in the matter of igniting ladies' hats. 



The use of a mirror does not seem to have come in 

 till 1716, whe^ Hertel used this valuable adjunct both 

 above and below the stage. He also used the bull's-eye 

 pattern of condenser. He was responsible for the 

 "mechanical stage" also, by means of which an object 

 could be moved to and fro, and rotated on the stage by 

 screws. 



Still later, 17 38, Lieberkuhn revived the single 

 microscope, which still has a considerable range of utility, 

 as shown by our president at the last meeting. His lenses' 

 were fixed in concave mirrors. 



.Wilson, 1746, was a good example of the age of 



