VH. PHOTOGRAPHY. 207 



extent magnifying may be carried without definition being lost to any sensible 

 degree. 



The peculiar bath-holder in which the small negatives were taken is also 

 shown. It has been described in the " British Journal of Photography," in 

 1866, with improvements in the almanacs of the same journal for 1874 and 

 1876. 



955a. Photographic Apparatus, by M. A. Chevalier, for 

 plan-drawing. M. J. Duboscq, Paris. 



956. Lichtpaus Apparatus, for photographing maps, plans, 

 &c. Remain Talbot, Berlin. 



957. Press used in printing a " Woodbury " permanent 

 photograph, with leaden mould imposition. 



Woodbury Permanent Photographic Printing Company. 



958. Photographic Portrait Objective D. 



Voigtldnder and Son (Chevalier von Voigtlander), Brunswick. 







958a. The same, No. 3. 



Voigtldnder and Son (Chevalier von Voigtldnder) , Brunswick. 



959. Photographic Lens for Astronomical Photo- 

 graphy. John Henry Dallmcycr. 



A double combination lens (rapid rectilinear) of 4" diameter and 30" 

 focal length, consisting of two symmetrical combinations, each having a focus 

 of 63", and composed respectively of a crown and flint-glass lens, united by a 

 permanently transparent cement to avoid reflections at the contact surfaces. 

 The flint lens occupies the exterior position in each combination. It is con- 

 cavo-convex, convex sides external. The crown lens is a meniscus, the con- 

 vex side of the same radius of curvature as the flint lens, and they are 

 cemented. 



The radii of curvatures are so apportioned between the lenses that the 

 spherical and chromatic aberrations are destroyed, or, in other words, the 



combination is aplanatic, and this for an aperture = -^- to +-. 



75 8 



The lens described (one of a series) was constructed and used for photo- 

 graphing the sun's corona. 



959a. Photographic Lens for Self-Recording Instru- 

 ments, i.e., Barographs, Thermographs, &c. 



John Henry Dallmeyer. 



A double combination lens (No. 2 C) of 2f" diameter and \" focus. 

 Consists of a cemented front and an open back-combination, having a very 

 large angular aperture, i.e., possessing great intensity. The front or cemented 

 combination is composed of a double convex crown lens, of unequal curva- 

 tures, the shallow side occupying the outer position ; and the flint lens, a 

 double concave, is united to the deep side of the crown, the adjacent surfaces 

 being identical. At an interval equal to the diameter of the front is posi- 

 tioned the back combination, composed of a flint lens concavo-convex, convex 

 side facing the front combination, and a crown lens nearly piano- convex, or a 

 crossed lens, with the more convex side nearest the flint lens, but of different 

 radii of curvature, and therefore not cemented. 



