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TRANSACTIONS OF THE AMERICAN INSTITUTE. 



empty head was incapable of taking in the whole of the charming- picture. 

 One of the dreams of the photographer has been of an instrument which 

 should embrace a large angle and thus satisfy the wants of the eye; but» 

 with the majority of the attempts in this direction came other evils, the 

 greatest of which was distortion of the maiginal lines. The aplanatic lens 

 of Grubble is said to comprise an angle of seventy degrees, but in a view 

 before me of Trinity College, Dublin, taken with this lens, there is a cur- 

 vature of the straight lines of the roof of more than one-eighth of an inch 

 in its length. Mr. Sutton's panoramic lens, a sphere of glass filled with 

 water, includes a very large angle, over one hundred degrees, on the base 

 line, but the pictures are produced on curved plates, which require curved 

 holders, baths and printing frames, and, in the case of architectural pictures,, 

 the right lines are distorted, unless the picture be bent to the curvature of 

 the plate upon which it was taken, and thus viewed near the centre of the 

 curvature. 



The Harrison and Schnitzer globe lens consists of two achromatic 

 meniscus lenses placed with their concave sides together, and so made that 

 their outer curved surfaces form part of a perfect sphere and the light is 

 admitted through an aperture placed mid- 

 way between the two lenses, i. e., in the 

 exact centre of the external sphere. The 

 annexed figure represents one of these in- 

 struments, A and B being the meniscus 

 lenses, and the centre opening through /A[| 

 which the rays of light pass. The focus of 

 such a lens one and three-quarter inches in 

 diameter is two and one-half inches for dis- 

 tant objects, measuring from the surface 

 of the back lens to the ground glass D. 

 The circle of light produced is five inches 

 in diameter, and from this may be cut the 

 ordinary three second square of a stereoscopic picture. The included angle 

 of light in the five inch circle is seventy-five degrees, and in a three-inch . 

 square picture cut from it is contained just four times the area of any 

 instrument I have ever tried, suited to similar work. The remarkable pro- 

 perty of this lens consists in its absolute correctness of reproduction. If 

 it is used for copying purposes, the marginal lines are copied as straight 

 as the originals, and, if a copy be made the same size as the original, the 

 photographic copy will, if laid upon the original, match it in every line. I 

 have said that the globe of two and a half second focus will make a circle 

 of light of five seconds diameter. Tliis is when a distant landscape is in 

 focus. If it is used for Cfjpying, the circle of light increases in diameter 

 as the object approaches the front lens and tfie ground glass recedes to 

 focus, so that an instrument which will cover a given size plate for views 

 will cover one of twice the size, when reproducing the size of the original. 

 As the lenses increase in size and length of focus, the plates covered 

 increase in size, and the amount of glass in the lenses bear a larger pro- 

 portion to the brass work in which they are mounted, and hence the included 

 angle of vision is increased, so that while in the two and a half inch globe 



