EARLY DAYS OF THE MICROSCOPE 



which the object to be examined was placed. Be- 

 cause these crude instruments were chiefly used for 

 the examination of insects they were known as 

 " Vitrea pulicaria " or *' Vitrea muscaria." Later 

 they were called *' Engyoscopes," and, after the 

 invention of compound microscopes, they were de- 

 scribed as '* Microscopia ludicra," as opposed to the 

 latter instruments, known as " Microscopia seria." 



The next stage in the development of the micro- 

 scope consisted in the introduction of lenses of very 

 short focal length, and, in 1665, Robert Hooke used 

 small glass balls, formed by fusing threads of drawn 

 glass, for this purpose. 



It was Antony van Leeuwenhoek, however, who 

 perfected these instruments. He brought an extra- 

 ordinary skill and industry to bear on the grinding 

 and polishing of minute lenses of short focal length. 

 Already in 1673 Regnier de Graaf wrote to the Royal 

 Society in London that Leeuwenhoek was making 

 glasses far superior to those of the great Italian 

 lens maker, Eustachio Divini. Leeuwenhoek's suc- 

 cess was largely due not only to his method of 

 grinding, but also to the skill with which he mounted 

 his lenses, which were accurately fitted into a 

 minute hole in a metal plate. The object to be 

 examined was firmly held in a stand and adjusted 

 by means of a screw movement. By this means, 

 and by the use of hollow metal reflectors, he suc- 

 ceeded in availing himself of transmitted light in 

 the case of transparent objects. Leeuwenhoek was 

 able to make immense advances with these instru- 



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