have been made and the faihires recorded in 

 the hterature. It has been evident always 

 that a successful x-ray microscopy would 

 open up fields of investigation closed to opti- 

 cal microscopy because of limited resolution 

 and to electron microscopy because of the 

 very limited penetration of electrons, thus 

 necessitating extremely thin specimens. All 

 such attempts until the one announced in 

 September, 1948, were unsuccessful, so that 

 focusing and image formation in a micro- 

 scope were generally considered to be im- 

 possible. Accepting the known fact of total 

 reflection of x-rays from mirrors at extremely 



Fig. 1. Arrangement of reflecting mirrors. 



REFLECTION MICROSCOPY 



small grazing angles of incidence. Prof. Paul 

 Kirkpatrick of Stanford University has 

 taken a great step forward toward a success- 

 ful solution of a seemingly impossible 

 problem. 



A concave spherical mirror receiving x- 

 rays at grazing incidence images a point into 

 a line in accordance with a focal length / = 

 Ri/2, w^here R is the radius of curvature and 

 i the grazing angle. The image is subject to 

 an aberration such that a ray reflected at 

 the periphery of the mirror misses the focal 

 point of central rays by a distance given by 

 S = l.bMr^/R, where M is the magnification 

 of the image and r is the radius of the mirror 

 face. The possible resolving power is such as 

 to resolve points separated by 70 A, inde- 

 pendent of wavelength. Point images of 

 points and, therefore, extended images of 

 extended objects may be produced by caus- 

 ing the x-rays to reflect from two concave 

 mirrors in series, particularly when crossed 

 at right angles to each other. Figure 1 gives 

 a schematic idea of the arrangement of the 

 mirrors of the apparatus, Fig. 2 reproduces 

 photographs of the microscope, Fig. 3 is a 

 reproduction of the photographed enlarged 

 images from a 350-mesh screen. This figure 

 shows, besides the full image from both mir- 

 rors (upper left), partial images from each 

 mirror separately (H, upper right, V, lower 



A B 



Fig. 2. Reflection microscope: (a) end showing x-ray tube (right) specimen, specimen holder and 

 mirror mount; (b) film end showing window for observing fluorescent screen. 



673 



