VII. PHOTOGRAPHY. 239 



Double convex crown and double concave flint ; back 

 combination. Double concave flint, and double convex 

 crown. Used from 1861 to 1864. 



(c.) Doublet, consisting of front combination. Double convex 

 crown and double convex flint ; back combination, 

 meniscus crown and concavo-convex flint. Used from 

 1864 to 1874. 



(d.) Symmetrical lens, introduced in 1874, and consisting of 

 front combination. Concavo-convex and meniscus lenses ; 

 back combination, exactly similar, the denser element 

 being on the outside in both cases. fioss fy Co. 



954. Photographic Lenses for Portraiture, showing 

 the progressive improvements from 1839 to present date : 



(a.) Original compound portrait lens. The first lens made in 



England by Andrew Ross for daguerreotype portraiture in 



1839. 

 (b.) Compound portrait lens, with Waterhouse diaphragms, in 



front, Date 1851. 

 (c.) Compound portrait lens, with Waterhouse diaphragms, 



giving a flat field. Date 1858. 

 (d.) Compound portrait and group lens, giving a* flat field, and 



straight marginal lines. Date 1874. Ross $ Co. 



954a. New Tourists 9 Photographic Apparatus for taking 

 Wet Plates without the use of Dark Teat, all baths and 

 chemicals being placed in water-tight compartments under body of 

 camera. Harvey ', Reynolds, and Company. 



954b. Photographic Lens with which the pictures of 

 Mr. Fox Talbot's Pencil of Nature were taken. (This is the first 

 publication of photographs printed from negatives on paper.) 

 Presented. B. B. Turner. 



955. Photographic Apparatus. " Poor man's photo 

 graphy," for wet collodion negatives of the smallest possible size, 

 but rapid and well defined. Twelve examples of negatives, 1 

 inch square, two framed and magnified positive copies, and the 

 bath-holder in which these negatives were taken. 



Prof. Piazzi Smyth. 



These negatives are on microscope slide glasses, and were taken with a lens 

 of rather less than 2 inch solar focus by Professor Piazzi Smyth, in Egypt, in 



1865. They represent scenes inside the Great Pyramid by magnesium light, 

 and outside it by daylight, including, in one of them, camels in motion. The 

 two positive copies on glass, each 10 in. high, are exhibited to show to what 

 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. 



