206 SEC. 7. LIGHT. 



I. PHOTOGRAPHIC APPARATUS. 



953. Photographic Lenses for Landscape, Architec- 

 ture, and Copying, showing progressive improvements from the 

 original single meniscus lens : 



(.) Single meniscus lens, used from 1851 to 1861. 



(.) Triplet, consisting of front combination. Double convex 



crown and plane concave flint ; middle combination. 



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. Ross $ 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 S? Co. 



954a. New Tourists 9 Photographic Apparatus for taking 

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

 chemicals being placed in water-tight compartments under body of 

 camera. Harvey, Reynolds, and Company. 



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, Royal Observatory, Edinburgh. 



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 



