35 
of Photogrammetry" (Figure 18). He declared: 
"My invention has for its object, producing a method of 
obtaining aerial photographs in such a manner that the pic 
tures can be converted into topographic maps, to delineate 
not only the horizontal positions and distances of the 
objects correctly, but from which the altitude of the 
objects can be quickly and accurately ascertained, and 
such results obtained without the aid of other field instru 
ments. My invention has also for its object, producing a 
method in which the results stated can be obtained in a 
simple manner with absolute accuracy." 
A Frenchman, L. Cailetet, using the newly developed roll film, 
devised a camera for use with unmanned balloons which would automati- 
21 
cally record the height reached by the balloon. His device 
(Figure 19) superimposed the image of an aneroid barometer on the 
film as each exposure was made. Describing his invention for the 
readers of La Nature, Cailetet remarked: 
"This apparatus was submitted to experiment for the first 
time on October 21, 1897, in an ascension organized by the 
Commission d' Aerostation Francoise, for the purpose of 
testing various automatic apparatus designed for the explora- 
22 
tion of the upper atmosphere."