446 TRANSACTIONS OP THE AMERICAN INSTITUTE. 



lenses may have been made with an external spherical focus, as is the Sut- 

 ton case, it will be difficult to produce a lens, made previous to the inven- 

 tion of this now described, composed of two achromatic meniscus lenses com- 

 bined as these are and producing a like result. The theory of operation 

 and mode of construction of the globe lenses admit of their being 

 readily made of various focal lengths, and thus by the use of a series of 

 instruments, the whole included angle can be made available on any size 

 plate that may be desired; the six inch focus covering a 6| seconds by 

 8| seconds plate, and the 12 seconds focus lens covering 14 seconds by 

 18 seconds, each including the same angle. One great advantage of short 

 focus lenses, when there is no spherical distortion, is in the appearance of 

 perspective produced. If, for instance, we would view a machine or 

 statue to the best advantage, we stand at such a distance from it as will 

 admit of our viewing the whole of it in the eye at once, and can then best 

 judge of its proportion. If now a picture be made by an instrument of 

 long focus, it will be so far away from the object to be depicted as to 

 make, as it were, too nearly a plane or flat view of it, deficient in perspec- 

 tive effect. With the very shortest focus of this new lens (the 2| seconds 

 focus), this perspective eflfect may be too much exaggerated, but with all 

 the other sizes it is not, and with the g'obe lens and with this only have 

 been produced pictures which seem to me to convey a just idea of size and 

 proportion. Some year or so ago, Messrs. E. and H. T. Anthony published 

 a series of stereographs of Niagara, which seemed to me when I first saw 

 them to bring to my mind all the wonders of the stupendous cataract, and 

 all to whom I have shown them seemed similarly impressed; it was not 

 until recently that I learned that they were taken with the Harrison globe 

 lens, thus furnishing another convincing argument in my mind of the value 

 of the instrument. I can not too strongly urge their adoption by photo- 

 graphers, and am proud of them as originating in America. The shortness 

 of their focus adds much to their portability, as the camera is maie smaller 

 than usual, and amateur field photography with the globe lens and dry 

 plates is a pleasure in place of a labor. Its advantages may be summed 

 up in a few words. Short focus, clear definition, wide angle of included 

 vision, absolute correctness of copy on a plane surface, and tolerably 

 quick work. It takes the place entirely of the orthoscopic lens, giving 

 absolute correctness to marginal lines, while the orthoscopic was only 

 approximately correct. It fills all the requirements of a lens for landscape 

 and architectural work, and is wanting only in the one thing of absolute 

 instantaneity of action. 



Philadelphia, March 10, 1863. 



[We may add to Mr. Seller's notice of the " globe lens " that this instru-. 

 ment has been found to reproduce military and other maps and plans with 

 a minute fidelity heretofore unattained; and by their use our army and 

 navy are furnished with photographic copies of manuscript maps and coast 

 survey plans, in which, as appears from the statements of the officers in 

 charge, there is no sensible distortion of the right lines, even on very large 

 plates. Eds. of Silliman's Journal.] 



