240 SEC. 7. LIGHT. 



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



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



956. Lichtpaus Apparatus, for photographing maps, plans, 

 &c. Romain Talbot, Berlin. 



957. Press used in printing a " Woodbury " permanent 

 photograph, with leaden mould in position. 



Woodbury Permanent Photographic Printing Company. 



958. Photographic Portrait Camera, D. 



Voigtldnder and Son (Chevalier von Voigtldnder)^ 

 Brunswick. 



953a. Photographic Portrait Camera, No. 3. 



Voigtldnder and Son (Chevalier von Voigtldnder). 

 Brunswick. 



959. Photographic Lens for Astronomical Photo- 

 graphy. John Henry Dallmeyer. 



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 reflection at the contact surfaces. 

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

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

 vex side of the same radius of curvature as the flint lens. 



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 aperture to. 



7 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 4^" focus. 

 It consists of a cemented front and an open back-combination, having a 

 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 a double concave 

 flint lens 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 placed the 

 back combination, composed of a concavo-convex flint lens, convex side 

 facing the front combination, and a crown lens nearly plano-convex, with the 

 more convex side nearest Ihe flint lens, but of different radii of curvature, 

 and therefore not cemented. 



The ratio of foci between the front and back combinations is 2 : 3 nearly, 

 and the radii of curvatures are calculated to produce well defined images for 



aperture = , and angle of picture = 30. 



959b. Photographic Lenses for the reproduction of maps, 

 plans, &c., as employed at the Home and Foreign Government 

 Topographical Establishments. John Henry Dallmeyer. 



