ORIGIN AND HISTORY 



London, which made him a Fellow in 1618. 

 His letters have been translated from the 

 old-fashioned Dutch which was Leeuwen- 

 hoek's mother tongue into English and 

 Latin; many of them were published in the 

 Philosophical Transactions from 1673 to 

 1723. A complete edition of Leeuwenhoek's 

 letters was never published, but a collection 

 of them appeared from 1695-1719 under the 

 title ^^ Arcana Naturae ope micro scopiorum 

 detecta" or "Mysteries of Nature Discovered 

 by Means of Microscopes." 



Some historians blame Leeuwenhoek for 

 his naive ignorance; others praise him as the 

 founder of bacteriology and protozoology. 

 By the end of the 17th century Leeuwenhoek 

 was the only earnest and scientific micro- 

 scopist in the world. He seems to have been 

 the first to really see and describe "ani- 

 malculae" (the "little animals"), including 

 spermatozoa and bacteria. 



There were many contemporaries and 

 followers of Leeuwenhoek who tried to imi- 

 tate him but they were seriously hampered 

 by the low quality of the optical lenses avail- 

 able at that time. Neither had they the 

 excellent mechanical skill for making their 

 own lenses as Leeuwenhoek had done, nor 

 did they have the exceptional keenness of 

 his eye. There is no wonder then that this 

 whole area was not ciuite respectable among 

 scientists and remained so for cjuite a long 

 time. Numerous indications of this attitude 

 can be found, for example in the London 

 Encyclopedia in 1829 in an article entitled 

 "Optics:" 



"Microscopes, though but toys compared 

 with telescopes, nevertheless deserve to be 

 rendered as perfect as possible; for they 

 yield not to them in the quantity and variety 

 of rational amusement which they are ca- 

 pable of introducing to us, though not of the 

 sublime description of the wonders of the 

 heavens. Compound microscopes, though 

 not so much to be depended upon for the 

 purposes of discovery and philosophical in- 



vestigation as single lenses, are still best 

 adapted for recreation." 



The preference of single lenses expressed 

 in this article over compound microscopes 

 has its reason in increasing awareness of 

 aberrations, of which especially chromatic 

 aberration is very harmful to the quality of 

 the images attainable with a compound 

 microscope. The so-called spherical aberi-a- 

 tion, brought about by the use of spherical 

 lenses, could be remedied to a large extent, 

 as Newton had shown in his ''Optics," pub- 

 lished 1704. But he also thought that the 

 chromatic abberation was unavoidable be- 

 cause the production of colors by dispersion 

 seemed to be inseparable from the refraction 

 necessary for the formation of images by 

 lenses. This had been found by Newton 

 experimentally. He also derived a mathe- 

 matical formula for dispersion which was 

 criticized by Euler in 1750 and a new formula 

 was proposed. However, about 80 years 

 later, Cauchy showed that Euler's formula 

 was untenable and suggested another. This 

 field of mathematical optics has been worked 

 on by many other scientists and mathe- 

 maticians up into modern times. 



Many experimental and theoretical in- 

 vestigations were made in the 100 years 

 following the publication of Newton's 

 "Optics" and it was found that the disper- 

 sion and refraction change in a different way 

 in going from one medium to another and 

 the problem was recognized to consist in 

 finding the proper combination of two or 

 more optical media. 



Development of Microscopy from 1723 

 to IVIodern Times 



The problem of manufacturing achromatic 

 lenses, at first for telescopes only, was solved 

 by several amateurs and scientists, either 

 entirely or partially independently. Among 

 them were Ch. M. Hall in 1729, a barrister 

 and amateur in optics; L. Euler, a mathe- 

 matician, in 1747; S. Klingenstierna, a math- 

 ematician, in 1755; J. Dollond, an optician, 



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