DR. G. W. ROYSTON-PIGOTT ON A SEARCHER FOR APLANATIC IMAGES. 603 
Explanation of the Plates. 
PLATE LI. 
Plate LI. is intended to represent the working powers gained by the use of the 
Aplanatic Searcher by means of comparative outline drawings of a given “ scale” taken 
by Mr. Aldous with the Camera under the magnifying-powers and objectives indicated. 
Fig. 1. The standard appearance of the Podura under the y- 5 -, and Powell and 
Le aland objectives. 
Fig. 2. Resolution of the lower beads of Podura. 
Fig. 3. The beads of the upper stratum. 
Fig. 4. Comparative magnifying-power of the objective with the searcher, and also 
in the ordinary way with a “ third” eyepiece, C, of 1 inch focal length. 
Fig. 5. General appearance of the wavy markings of the Podura, consisting of beaded 
ribbing faintly visible here with a pocket-lens. 
Fig. 6. Both sets of beading exhibited at once. 
Figs. 7, 8. Ordinary and extraordinary appearance of Lepisma. 
PLATE LII. 
This Plate shows the image-test arrangements of the objectives and object of which 
a miniature is desired, and also the construction of the searcher. 
M. The divided milled head of the traversing aplanatic searcher, consisting of separable 
lenses, A, B, having a variable interval, otf, between them. The searcher tra- 
verses the draw tube, into which is fixed the eyepiece E. R, M are adjusting 
milled heads of the stage supporting the image objective O' (fig. 1 a). 
O, O', fig. 1, fig. la, are the objective to be tested and the miniature-forming yg- im- 
mersion objective, giving an image a of the object Q, or double disks A, illu- 
minated by a lamp, c>. 
y represents the focal adjustment, and 
(3 the aberrameter inserted into the nose of the microscope containing two revolving disks 
forming central and peripheral stops. 
Fig. 2 represents the course of the rays from the object Q to the last focal image q n p„ 
erected. 
4 o 
MDCCCLXX. 
