19 
lines, all parallel to the conjoining line of the two principal points of the frames, in which 
bundle each line is a united nuclear beam of the correspondence. (Fig. 12 and 13). 
Therefore setting a point on the image line, furnished by one of the photograms, its 
homolog on the conjugated image line of the other photogram, will necessarily be found 
  
Fig. 12. Homologous point identification in the normal arrangement 
with horizontal base. 
on the parallel to the conjoining line of the principal points. For such an identification the 
homolog-comparator will function more as a comparator than as a homologoscope. (See 
Fig. 11 and 13). 
In the case of oblique take arrangement, the procedure is also simple. Let us observe 
meanwhile that there almost never happens the necessity of using an oblique take arran- 
gement with a horizontal take base. Besides, from an oblique take arrangement with a base 
  
Fig. 13. Homologous point identification in the normal arrangement with 
tilted base. 
tilted in any manner, it is possible to arrive at a take arrangement in every way equivalent 
to the normal one (plates in the same plane) if the proper equal elevations are given to 
both of the take axes. The typical case of the oblique take arrangement could instead verify 
itself when there is desired, from a normal take arrangement with base tilted (therefore 
with the take cameras' axes horizontal) to impose to each of these axes equal angular 
elevations ¢, and ¢,. We shall then have the two take frames in two parallel planes, this 
being a characteristic condition of the take obliquity (Fig. 14). In said case the nuclear 
points will have, in the two reference systems adopted, coordinates equal and of the same 
sign and the nuclear beams of a same pair will always result parallel. (Fig. 14). Therefore,