PHASE MICROSCOPY 



Fig. 2. The first contrast pictures (Fig. 1.) 

 were made by using a circular aperture in the con- 

 denser and a likewise circular, clear area on a 

 lightly-sooted objective lens surface. The left hand 

 picture shows the path of light in the system; 

 above and below are the objective and condenser 

 apertures in a perpendicular view. In the picture 

 to the right is shown the anoptral method devel- 

 oped later. The non-diffracted rays penetrate a 

 heavily light-absorbing, non-refiecting area in the 

 objective. 



suits could be obtained by using an annular 

 diaphragm opening in both the condenser 



not college-trained, understood only Dutch, and 

 did not even write his own language like an edu- 

 cated man. The microscope consisting of objective 

 and eyepiece had been discovered and used before 

 Leeuwenhoek was born, but he never possessed 

 one. He saw blood corpuscles, sperm-cells and 

 even bacteria with his instrument, which con- 

 tained only a single tiny lens. Yet he was able to 

 make such a number of microscopical observations 

 which he communicated to the Royal Society of 



and the objective, the transmission of the 

 objective diaphragm being 50 per cent. Liv- 

 ing specimens such as 3'east cells appeared 

 very clear and sharply defined with this sys- 

 tem, and had an agreeable brownish tint on 

 a bright background. The cells showed 

 darker the more the refractive power of their 

 content exceeded that of their surroundings, 

 i.e., the better their state of nourishment 

 (Fig. 1). 



Later the author found that the phase- 

 contrast microscope, developed on a theoret- 

 ical basis by Zernike, had been constructed 

 by the Zeiss Optical Works. When the author 

 looked into a phase-contrast microscope for 

 the first time he was surprised to note the 

 similarity of the images obtained with it and 

 with his own ecjuipment. Both of them cer- 

 tainly had annular condenser apertures, but 

 the phase-contrast objectives had light - 

 absorbing annuli whereas the author's had an 

 absorbent coating recessed in the form of a 

 ring. But the effect produced by the images 

 was not identical. Round each light-refract- 

 ing detail the phase-contrast microscope ex- 

 hibited haloes which had no counterpart in 

 reality. The author's microscope showed 

 none of these haloes, and the gradation of 

 the different intensities of contrast, depend- 

 ing on their light-refracting properties, was 

 agreeably soft. 



During his first experiments the author 

 made an observation which was afterwards 

 to prove significant. If the coating of soot 

 in the objective was not recessed in the form 

 of an annulus, but complementarily applied 

 so that the light coming from the condenser 

 diaphragm passed through this annulus, an 

 image was obtained which exhibited the op- 

 posite properties (Fig. 2). The author re- 

 sumed his experiments in this direction in 



London that the Dutch have recentlj^ published 

 them in four large volumes. Nor were the inven- 

 tors of the first achromatic microscope objectives, 

 Aepinus and Beelsnyder, professional opticians. 

 The former was a Privy Councillor and the latter 

 a cavalry officer (see also p. 458). 



478 



