' Microscopes 3 1 



The need for better lenses led to work on achromatic lenses in an 

 attempt to eliminate the undesirable color fringes (various color bands) 

 seen around objects being observed with high power, single lens objec- 

 tives. Vincent and Charles Chevalier made an improved achromatic 

 microscope in 1824 with a magnification of 1800x. 



Robert Brown discovered the general occurrence of the nucleus in 

 plant cells in 1831. ^ 



Dujardin, the French zoologist, in 1835 observed the jellylike, slimy 

 material in animal cells which later was found in living plant cells, and 

 the term protoplasm was applied to this material by von Mohl in 1846. 



Jacob Schleiden and Theodor Schwann, through microscopic studies 

 of many plants and animals, promulgated the cell principle in 1839. 



There were only about a dozen microscopes in the United States in 

 1831. Instructors were using them by 1850, and students began using 

 them as early as 1875, but they were not in general student use until 

 about 1890. 



Charles A. Spencer (1813-1881) built the first American microscope 

 (1847) and built several models for instructor and student. Robert B. 

 Tolles (1824-1883) was another early American microscope builder; he 

 started as an apprentice of Spencer but established his own business in 

 1858. He is famous for his improvements on objectives and for his 

 invention of the homogeneous immersion objectives. In the latter, a 

 drop of the proper type of liquid is placed on the cover slip on the slide 

 and the immersion objective is made to contact the liquid, which acts as 

 a type of lens to assist in higher magnifications. We may use oil immer- 

 sion objectives for high magnifications. Riddell invented a binocular 

 microscope in New Orleans in 1851 so that both eyes could be used in 

 viewing an object. Edward Bausch (1854-1944) made his first micro- 

 scope in 1872; he was the son of /. J.^Bausch (1830-1896), the founder 

 of the Bausch & Lomb Optical Company. 



Ernst Abbe (1840-1905) joined the Carl Zeiss Co. in Germany in 1866 

 and invented the Abbe condenser (1872) and a camera lucida (1882) 

 for making drawings of microscopic objects. 



From our brief and necessarily incomplete consideration it is apparent 

 that many individuals over a long period of time have made their con- 

 tributions to the improvements of the microscope (Fig. 5). This is 

 characteristic of science — one person merely takes the work a short dis- 

 tance, to be carried forward by others who will profit by the errors and 

 discoveries of their ancestors-in-science. 



