CONSTRUCTION AND MANAGEMENT. 



16V 



The invention of the Compound Microscope is attributed to 

 Zaccharias Janssen, whose portrait we are enabled, through the 



Fig. 31. — Wilson's Microscope, 1740. 



courtesy of Mr. Wynne E. Baxter, to present to our readers. 

 Janssen was a small optician of Middleburg, whose residence was 

 attached to the Church. 



An instrument called " Janssen's Microscope " is still preserved 

 at Middleburg, which, according to Harting, can be referred back 

 as far as his period without its being the original instrument. This 

 instrument was shown at the Antwerp Exhibition. 



The Microscope, Fig. 32, consists of four tubes, made of iron 

 and soldered together, coated inside with tin. The outer tube A 

 is of the greatest diameter, and contains the tubes B and C, which 

 slide into it. The tube B contains, within itself, a fourth tube^', 

 having, at its lower end, a bi-convex objective lens of 2,2 inches 

 focus. The ocular lens, of about 3 inches focus, is plano-convex, 

 and is held in a wooden cell by a ring made of iron wire. The 

 tube C which contains it is terminated at the upper end by a con- 

 cave diaphragm. The tube B\ which contains the objective, is 

 terminated at the upper extremity by a diaphragm, flush with the 



