ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 635 



plane images drawn upon paper shall appear to be in relief as if looked at 

 through a stereoscope." 



Hand Binocular magnifying glasses are also described and illustrated. 



Objectives and Eye-pieces. — In the settings there are several pecu- 

 liarities. " Two openings, s s' (fig. 12 of plate and fig. 155), made in the 

 outer tube of the objective, allow of the entrance of the light condensed 

 by prisms, mirrors, or reflectors upon an opaque object even with the 

 employment of the greatest magnifying power, even with glasses where 

 the system of immersion is employed. Each of these openings is furnished 

 with a small thin tube of silver or copper in order to prevent the dust from 

 entering between the first and second lenses. This light may be polarized 

 by means of a prism made of Iceland spar or any other polarizer, and 

 coloured or monochromatized by a lens or plate of rock crystal." 



Both objectives and eye-pieces are mounted on revolving holders/, with 

 spherical bars E and E', as shown at fig. 12. The revolving holders may 

 be connected together by a rod, fig. 13, so that the eye-pieces and objectives 

 may be changed simultaneously. 



The "optical part" is, however, the most curious of the patentee's 

 suggestions (figs 14-24, plate XIV.). " It is composed of lenses or series 

 of lenses, the arrangement, form, and composition of which are special. 

 The fii-st lens is plano-convex ; the second, which may be composed of two 

 parts, is a complete ellipsoid, or formed of two parts of ellipsoid, or hyper- 

 boloid, or paraboloid, or even simply a spheroid. In certain cases it may 

 be divided into two parts (fig. 15) plane or cut out at their centre, with 

 such a curve (fig. 16) that the rays which come from the object S shall 

 arrive at the face d, leave it, and after crossing each other shall penetrate 

 the face b, and emerge from the face c after a fresh refraction, which shall 

 render them sensibly parallel. They are rendered divergent by the 

 periscopic lens M, fig. 14. If this lens is replaced by another which is 

 plano-convex or a divergent periscopic meniscus (figs. 17 and 18), the 

 rays will cross each other again at /, and the image will be again turned 

 round. The lens, instead of having its centre cut out, may have it 

 formed of a lump thicker than the rest ; it may also be cut or shaped as 

 seen at figs. 19 and 20. The lenses may be neither complete ellipsoids 

 nor hyperboloids, and may be set at variable distances (figs. 16, 19, and 

 20). The lenses L, L^, are shown on a scale larger than the real size. 

 This arrangement of object-glass is applied in all its variations to all 

 optical apparatus to which it may be applicable, especially to photographic 

 apparatus, as well to simple as to compound ones, which will be hereafter 

 alluded to." 



" The improved eye-piece is composed of a convergent periscopic or 

 non-periscopic meniscus, placed as shown at fig. 14, and of an ordinary 

 eye-piece. Fig. 21 represents an eye-piece in which the divergent peri- 

 scopic or non-periscopic glass is placed near the eye-piece." 



"All the improved lenses are composed of glass in simple concentric 

 layers, or in groups laid one upon the other and rendered adherent or 

 fastened together, and arranged under conditions of thickness, arrangement, 

 curvature, dimensions, and powers of refraction and dispersion even variable 

 from the centre to the edge, such that not only are they completely achro- 

 matic, but moreover, whatever may be their form, even spherical, they may 

 be completely deprived of spherical aberration, chromatic aberration, 

 astigmatism, and distortion, and give the chemical focus at the same 

 mathematical point as the optical focus. These layers, either coloured or 

 not, are applied to the glasses of all optical instruments, spectacles, eye- 

 glasses, field-glasses, and telescopes, and not only will these superposed 



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