JOURN. R. MICR. SOC. 1907. PI. III. 



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Fig. 6. — riciimsigma angulatitm (mounted dry), photographed by a divided 

 beam. Condeuser beam S.A. =0-225/; (W.A. = 0-225). Stop S.A. = 0-2 /. 

 The annulus in which the six diffi-acted lieams lie, has S.A. =1-7/ (equivalent 

 to N.A. 1-7). The central beam is unsymmetrical ; thus S.A. = 0-G + 0'2 = 0-8 

 in the long diameter, and S.A. = 0-25 + 0-2 = 0-45 in the short diameter. The 

 image may be considered as a composite, in which regular images from these two 

 sources are blended. Magnification 320 x 14 = 4480. 



Fig. 7. — Staphijlococcuft. In the top panel as photographed l)y the beam shown 

 in the marginal photograph, but without the stop. Condenser beam S.A. = 0-8 f 

 (W.A. = 0-S). Objective S.A. = / (N.A. = 1). Magnification 814 x 20 = 6280. 

 In the second panel the same specimen photographed by the same lieam stopped 

 as shown in the marginal photograph. Stop S.A. =0*65 /. Condenser beam S.A. 

 = (0-8 +0-G5) /= 1-45 / (equivalent W.A. 1-45). Objective S.A. = (1 + 0-65) 

 f = 1 -65 / (equivalent N.A. 1 - G5). Same magnification as before. 



Fig. 8. — Sketch of the same specimen, the subject of Fig. 7. Illumination 

 the same. Magnification the same. 



