sults achieved to date, and the accuracy obtained. The thorough examin- 
ation of the instruments is now under way at the Institute of Geodesy 
and Topography of the Engineering Faculty of the Rome University. 
DESCRIPTION OF THE INSTRUMENT 
A clear idea about the instrument one gets from the diagram fig. 1 
completed by the photographs fig. 2 and 3. 
FACCIA CATETO TETTO FACCE IPOTENUSE SEMIARGENTATE 
  
FACCIA CONTROTETTO 
  
Fig. 6 —  NISTRI ROOF COMPOSITE PRISM — Tetto = Roof; Facce ipotenuse 
semiargentate — semi-silvered hypothenuse sides; Base — base; Facce controtetto = coun- 
ter-roof side. 
From the examination of these first pictures one can see first of all 
that the instrument can be divided in the following main parts, if both 
the manufacturing and the operative sides are considered: 
a) base; 
b) projecting unit; 
c) telegonioscopic unit; 
d) coordinatometer unit and system for adjusting the base; 
e) unit of the pencil bearing coordinatograph; 
f) unit of the controls, transmissions, gears, counters. 
And now let us examine each of these groups separately: 
a) The fundamental structure, which has to support the proper 
plotting organs, is represented by the base (see diagr. 1 and fig. 2), which 
is composed of: 
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