July 19, 1921 abstracts: optics 311 



DosNE. Compt. Rend. 158: 473-474. 1914. 



Raymond-Barker, E. Electrician 72: 743, 744 and 783. 1914 



Waggoner, C. W. Phys. Rev. 3: 500. 1914. 



Rainey, R. M. Electr. World 65: 848. 1915. 



Lenner, E. Electro, techn. Zeitschr. 36: 598. 1915. 



Urie, F. D. Pop. Astron. 23. Nov. 1915. 



PouLSEN, R. M. Electr. World 68: Nov. 1916. 



Culver, C. A. Joum. Frankl. Inst. 187. May 1919. 



Abraham, Block. Compt. Rend. 169: 282-285. Aug. 1919. 



Campbell-Swinton, A. A. Wireless World 8: 641-648. Dec. 1920. 



Turner, L. B. Electrician 83: 4, 5, 34, 35, 554-557. 1919. 



HoxiE, J. A. Elektrotechn. Zeitschr. 41: 73.3-734. Sept. 1920. 



Creed Co. Ltd. and D. McLennan. The Engineer. 130: 366. Oct. 1920. 



Latour, M. L'Electricien. 51: 452. Oct. 1920. 



HoxiE, J. A. Radio Rev. 1: 781. Dec. 1920. 



Campbell-Swinton, A. A. Sci. Amer. Monthly. 3: 155-156. Feb. 1921. 



CouRSEY, P. P. Wireless World 8: 761-764. Feb. 1921. 



Wallace, S. T. Wireless World 8: 768-769. Feb. 1921. 



Brun, J. Radio Electricite 1: 477-487. March 1921. 



Pratt, H. Proc. Soc. Rad. Eng. 9: 174. Apr. 1921. 



ABSTRACTS 



Authors of scientific papers are requested to see that abstracts, preferably prepared and' 

 signed by themselves, are forwarded promptly to the editors. The abstracts should con- 

 form in length and general style to those appearing in this issue. 



OPTICS. — The contrast sensibility of the eye as a factor in the resolving power 

 of the microscope. Fred. E. Wright. Journ. Opt. Soc. Amer. 2:101- 

 107. 1919. 



In this paper three factors of importance in high-power microscope work 

 are emphasized, namely: (1) The use of a polarizing prism to eliminate 

 that part of the field-light which does not contribute to the diflfraction pattern 

 in the image and hence tends to reduce the contrast and to decrease the 

 sharpness and crispness of the image. This phenomenon arises because 

 diffracted beams, which emerge from gratings whose interval is of the order 

 of magnitude of half a wave length of light, are sensibly polarized in a plane 

 normal to the lines of the grating. (2) a Diaphragm of the rectangular 

 type, for use in the image plane of the eyepiece in order to cut out all light 

 except that from the particular object under examination. The field should, 

 however, cover at least 10°. (3) The importance of a field intensity of 

 illumination approaching that of daylight and best adapted for the eye at 

 any particular time. The simplest method for securing this is by means 

 of a substage polarizer in conjunction with the polarizing prism ; the polarizer 

 can be rotated, and with it the intensity of illumination of the field varied. 

 These factors are not important for ordinary observations, because the 

 resolving power there required is not great; but in high-power, critical work 

 they are significant and enable the observer to accomplish with comparative 

 ea,se that which under other conditions is a matter of difficulty. F. E. W. 



