Bache.] ^^^ [May 6, 



To enable a traverse line to form a portion of a general survey, 

 there must be means adopted to place at least its initial and termi- 

 nal points in relation to that survey, whereby all intermediate 

 points fall into due relation with it. 



This premised, I will now describe how my plan for introducing 

 precision into balloon photogrammetry could be applied in various 

 useful ways for delineations of portions of the earth's surface. 



The appliances needed for carrying out the plan are a small 

 spherical balloon capable of supporting a light photographic appa- 

 ratus, swung in gimbals, and protected from injury in descent by a 

 thin encircling cylinder of metal or of wood. A zone of cord 

 would pass horizontally around the balloon, to which would be 

 attached four equidistant guys of the size of codfish lines. A 

 broad colored stripe would pass vertically around the balloon. 

 From below the balloon would depend reophores enclosed in a 

 graduated cord, the graduation serving the purpose of adjusting 

 the balloon to any given height above the earth. The reophores 

 would be electro-magnet ically connected with the shutter of the 

 camera, actuated from the ground by a small, but strong, galvanic 

 battery. 



The balloon, being inflated, would be compelled, by means of 

 tlie four equatorially fastened guys, to assume a position regulated 

 as to height by the graduated cord. This height will have been 

 previously determined upon with reference to the scale of the map 

 that may be desired, the focus of the camera having also been ad- 

 justed with reference to the contemplated height of the instrument 

 above the earth. The position of the balloon would be over the 

 middle of a given link of a traverse line, the orientation of the 

 camera being secured by causing the vertical stripe on the balloon 

 to range along the given link of the traverse line. Two disks, 

 made of hoops covered with white cotton cloth, one of which 

 should be larger than the other, would give on the photograph, 

 points representing the termini of the link corresponding to those 

 on the ground, and the direction in which the link, as a portion of 

 the traverse line, is lying. 



A very low grade of accuracy could be obtained by the balloon 

 photogrammetrical process by the method of omitting all angular 

 and linear measurements on the ground, and letting the balloon 

 camera, placed in a generalized position with reference to the parts 

 of a traverse line, accomplish the whole work of determining the 



