4 
The use of this device is quite obvious, once the direction of the 
instrument bridgings according to the increasing values of the X coordi 
nate is laid down. It is in fact set and levelled first on the righthand 
camera, holding the last photograph bridged and then passed on to the 
lefthand camera to which the same photograph is transferred, to repro- > 
duce as faithfully as possible, the primitive external orientation which is 
actually defined by the preceding w, 9 and x. 
3. The experimental tests carried out had as their main aim the setting 
up of the procedure best suited to realize analogical aerial triangulation 
at Stereosimplex III, both when using the above mentioned device and 
when not. 
According to the practice usually employed in experimental research 
work by Commission A of O.E.E.P.E. (3) the various tests were pre 
ceded by a suitable adjustment of the instrument used, — the one 
marked 00112 — by carrying out the controls and adjustmens laid 
down by the manufacturer (2). After these operations we then checked 
the plano-altrimetric projection of the projection cameras by means of 
a pair of precision grid-plates (Gitterplatte N. 250 and Nr. 257), 
engraved by the Verkaufs- A.G. Heinrich Wild of Heerbrugg with a 
mesh of 20x20 sq. mm. 
After checking wheter the mean square errors of projection obtained 
during this check agreed with those considered characteristic for the 
said type of instruments (4) we then passed on to determine the zero 
position of the instrument scales, and effected some tests to check that 
the conditions of absolute orientation (5) had been actually reproduced, 
taking as a reference the space model defined by the above grid pair. 
After satisfactorily completing all above mentioned preliminary 
tests, we then carried out two different analogical bridging of the 
same pair of grids. The first one was carried out by using the device, 
for the control of values m, 9 and x, the second by means of the 
simple visual transfer of the same values. 
The procedure chosen for connecting the two grids, considered as 
two ideal photographs, was that of a simple spacial bridging, commonly 
known as free bridging. The relative orientation of the grids, for the 
operator’s convenience, was realized using the Von Gruber optico- 
mechanical method.