ORIGIN AND HISTORY 



was entirely filled with water. Hooke nat- special requirements of diversified applica- 



urally did not know this explanation but tions leading to detailed specializations of 



Amici in 1850 tried to make use of this microscope design and methods of use which 



principle. Obviously the effect would be the deviate more or less from tradition, 



more useful the more similar the refractive Examples of this development are such 



power of the medium of the interspace be- fields as interference microscopy, polarizing 



tween the object and the front lens came to microscopy, X-ray microscopy, and the so- 



the refractive power of glass. Amici tried called flying spot microscopy. Also belonging 



other liciuids, e.g., glycerin and oil, with in this group are the reflecting microscope, 



some success. the fluorescence and the phase contrast mi- 



These problems were brought to the atten- croscope, which are briefly described in the 



tion of Abbe by English friends with a re- following. 



quest for investigations. He complied only The Reflecting Microscope. The prin- 

 hesitantly because the great amount of work ciples of a reflecting microscope were first 

 necessary did not seem to him to be justified described by Isaac Newton (1672) in a letter 

 by only limited apphcability, as for instance to the Royal Society in London. He might 

 in metallurgy. But he measured and tried a have realized that the objective of his re- 

 great number of liquids, about 300, and fleeting telescope, described twenty years 

 found the best to be cedar oil. The next step before, could be used as a microscope objec- 

 was to modify the objective lens so that it tive of long focal length if the light travel 

 would be better adjusted to the optical data through the instrument would be reversed, 

 of the oil. In this way the old idea of Des- In the following 100 years other inventors 

 cartes of optically homogenizing the path tried this principle also on the other reflect- 

 of light through several media, which he had ing telescope types known at that time, 

 tried with his crude water tube, found a re- However, about 1824 this line of develop- 

 vival in a refined manner in modern times. ment practically came to an end because of 



With apochromatic and homogeneous the introduction and further improvements 



immersion systems the optical microscope of achromatic lenses. 



was approaching the limit of its power of A new phase began in 1931, induced bj^ the 



resolution, which is about 250 millimicrons important advantages which reflective sys- 



for visible light, permitting the observation tems have over refractive systems for special 



and identification of most bacteria. This applications. These are the absolute achro- 



limit was shown by Abbe to be determined matism, the long working distance, and its 



by the wave length of the light used for unlimited applicability for a very wide range 



observation. of wavelengths. Depending on the special 



About the results of his experimental and conditions several distinct groups have been 



theoretical investigations Abbe reported in developed during the last 30 years, 



a great number of publications beginning in For single mirror objectives materials like 



1869. His complete theory of the microscope quartz, lithium fluoride and other synthetic 



appeared in periodicals from 1888-1895. inorganic crystals are used for the ultraviolet 



and the infrared region. The practical use of 



Recent Lines of Development 



these systems was found to be awkward in 



The microscope had been found to be an some cases because the customary micro- 

 instrument with a very wide general appli- scope stand and its accessories, which had 

 cability in many fields of research and devel- their own long line of development, usually 

 opmental technology. It could be expected could not be used. Active in this field were 

 that with the further growth of these fields men Hke R. Smith, 1738; K. Schwarzschild, 

 needs would arise which would demand 1905; H. Chretien, 1922; B. K. Johnson, 



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