of the lens (3). After having been reflected by the small mirror (4) solidal 
to the primary axis of the gyro, the pencil meets with the lens (5), the 
focal length of which is equal to that of the lens (6) of the taking camera. 
The’two mirrors (7) and (8) reflect the image on to the plane of the sensiti- 
zed surface. The initial adjustment of the instrument is made so that when 
the principal axis of the camera is vertical, the two cross-wires are placed 
each on one line connecting the collimating points. 
The take with tilled axis will then appear as per diagr. B. In this 
diagram, the dotted lines represent the parallel lines to the reading lines 
run by the coordinatometer, and their point of intersection represents the 
plumb point which is looked for. 
  
  
  
  
  
  
B) 
The device has been realized in order to enable a series of systematic 
experiences, for giving the elements requested in order to determin its 
accuracy. The tests are still under way, but their first results are so 
encouraging to deserve being commented. 
The gyroscope employed for this experiment was purposedly manu- 
factured, with special attention to some part: it is of the electrical type 
with ball erector, OMI system. Its behaviour has beeen studied through 
systematic trials which we are going to summarize.