for uniting Large Binocular Photographic Pictures. 107 



decided upon constructing the instrument without the box alto- 

 gether, as an unnecessary appendage when the telescopes were 

 used ; and it now appears very much like an opera-glass with 

 the two telescopes converging outwardly, so that the directions 

 of sight cross each other. 



The instrument, exhibited in fig. 3, is made capable of two 

 separate adjustments : one to accommo- 

 date the positions of the telescopes to the 

 distance of the eyes from each other, the 

 other to give the degree of convergence 

 requii'ed. The first object is attained by 

 placing the two telescopes on the extre- 

 mities of a support like the letter V, 

 placed vertically, its two branches open- 

 ing and closing on a hinge; and the 

 latter object by making each telescope 

 turn on a vertical axis, which must be 

 directly below the eyepiece in order that 

 the one adjustment may not disturb the 

 other. When the instrument is placed 

 on a stand, two other adjustments are 

 necessary : one to bring the field of view 

 to the same elevation as the pictures, another to bring the plane 

 of the axes of the telescopes into parallelism with the upper or 

 lower margins of the pictures, or in other words, to give the two 

 telescopes exactly the same elevation, it being pi-eviously under- 

 stood that the pictures are placed with their upper or lower mar- 

 gins in the same horizontal straight line, and the said margins 

 passing through corresponding points in the two pictures. The 

 former purpose is effected by inclining the V support backward 

 or forward by means of a second hinge placed below it, having 

 its axis at right angles to the axis of the hinge connecting the 

 two arms of the V. The latter adjustment is attained nearly by 

 the primary construction, and by observing that the arms of the 

 V are opened equally ; but is completed by two screws beneath 

 the telescopes, by means of which the outer extremity of either 

 may be raised or depressed. The focal length of each telescope 

 must also be attended to as usual. Five adjustments are thus 

 necessary, which should be made in the following order : — 



First, each telescope is carefully adjusted to the proper focal 

 length, so as to give clear vision. Secondly, the telescopes are 

 brought to the width between the eyes by opening or closing the 

 arms of the V, observing that they are opened equally. Thirdly, 

 they are turned together, upward or downward, according to the 

 elevation of the pictures, by means of the lower hinge. Fourthly, 

 the telescopes iinist be brought to their proper inclination towards 

 each other ; that being done by turning each separately upon its 



