LICTTT (OPTICAL) MICROSCOPY 



"Moments of Discovery" ed. by G. Schwartz 

 AND Ph. W. Bishop, Basic Books Inc., New 

 York, 1958. 



King, H. C, "The History of the Telescope" 

 Sky Publishing Corp., Cambridge, Mass., 

 1955. 



"Modern Methods of Microscopy" ed. by A. E. 

 ViCKERS, Butterworth Scientific Publica- 

 tions, London, 1956. 



RoosEBOOM, M., "Microscopium," Leiden, 1956. 



DoBELL, C, "Antony van Leeuwenhoek and his 

 Little Animals," Russell and Russell, Inc., 

 New York, 1958. 



"Origin and Development of the Microscope" as 

 illustrated by the Catalogues ... of the Royal 

 Microscopical Societj'. ed. by A. N. Disney. 

 The Royal Microscopical Society, London 

 1928. 



HOPPE, E., "Geschichte der Physik," F. Vieweg 

 AG, Braunschweig, 1926. 



RosENBERGER, F., "Geschichte der Physik," (3 

 vols.), F. Vieweg AG, Braunschweig, 1890. 



Dannemann, F., "Die Naturwissenschaften in 

 ihrer Entwicklung und in ihrem Zusammen- 

 hang," 2. ed. W. Engelmann, Leipzig, 4 vol- 

 umes, 1920-23. 



Articles in Isis, Scientific American, American 

 Journal of Physics, Science, Forschungen zur 

 Geschichte der Optik, Zeitschrift fur Instru- 

 mentenkunde, and others. 



E. K. Weise 



PARTICLE SIZE AND SHAPE MEASUREMENTS 

 AND STATISTIC (See also pp. 406, 408) 



Particle Size Methods 



The microscope for making particle size 

 measurements should be equipped with a 

 graduated mechanical stage, achromatic or 

 apochromatic objectives including an oil 

 immersion objective, a substage condenser, 

 and a graduated fine focusing adjustment. A 

 revolving nosepiece is desirable which can 

 be used to attach three or four objectives, 

 preferably parfocal, to the microscope. A 

 monocular microscope is preferable to the 

 binocular for highly critical work. A phase 

 contrast microscope is often useful for meas- 

 uring particles of low contrast, and a polar- 

 izing microscope is useful when differentia- 

 tion among various types of particles or 



identification of particles is desirable. The 

 light source should be equipped with a con- 

 densing lens and a field diaphragm, and 

 should be focusable. 



A number of accessories are either neces- 

 sary or highly convenient. Particle diameters 

 are generally measured with eyepiece (ocu- 

 lar) micrometers which consist of scales to 

 be placed in the focal plane of the ocular. A 

 number of types are available and the type 

 used depends somewhat on the definition of 

 diameter which is employed. If the diameter 

 is defined in terms of actual dimensions of 

 the particle, a linear scale is desirable. 

 "Globe and circle" micrometers are con- 

 venient for rapid sizing, the diameter being 

 defined as the diameter of a circle whose 

 area is equal to the projected area of the 

 particle. Filar micrometers have either a 

 movable scale or a movable cross hair and 

 fixed scale. Ocular micrometers must be cali- 

 brated for every combination of objective, 

 ocular, and tube length used, and the cali- 

 bration is usually accomplished with a stage 

 micrometer with linear rulings. 



Another useful accessory is the dark field 

 condenser, which often provides increased 

 contrast. A condenser with central stop is 

 useful for fairly large particles, but the 

 "Cardioid" condenser is preferred for par- 

 ticles having diameters close to the limit of 

 resolution of the microscope. 



Special devices which produce vmiform il- 

 lumination of opaque objects by reflected 

 light are often very helpful. The illumina- 

 tion may be vertical or annular. 



Particle size distributions are sometimes 

 made from photomicrographs. Advantages 

 are less eyestrain and a permanent record of 

 the appearance of the particles; disadvan- 

 tages are the additional time-consuming steps 

 and less flexibility in the examination of a 

 field. Microprojection equipment is often 

 useful, especially if the images can be pro- 

 jected on a disposable screen such as a sheet 

 of white paper. The images can be checked 

 off as measured, thus avoiding duplication. 



464 



