Ing. Nistri gets thus rid of the restraints represented by the ties cf 
th» mechanical transmission, which are sometimes a source to remarkabie 
difficulty, and consequently he makes the adjustments of the coordinato- 
meter carriages easier. 
As it will be suitably illustrated in the following chapters this new 
principle, representing a generalization of Porro's principle and further- 
more the introduction of the whole transmission by means of electro-ma- 
gnetical systems, give the instrument a particular character, make its ad- 
justment and manufacture easier, and — what is undoubtedly a remark- 
able fact — allow to carry out at the same time several cartographies, 
i 
Scamottaggio 
triang. spaziale 
        
   
   
  
  
   
   
   
    
  
Pr. Amici D, J GN "ny 
$mezzamento , 
verticale 
$mez2amento 
orizzontale 
Distanza 
oculari 
a 
$ 
Piccoli 
spostamenti à | To d #0. 
Piccoli 5 ; : 
spostamenti £Q 
X Disegno 
X Modello m i En 
> : 3 3 ; Relais 
Z Modello 
Y Modelo 
Yo isegno Inter, ‘ 
Fig. 4 — Smezzamento = correction for coincidence; verticale — vertical; orizzonta- 
le = horizontal; Distanza oculari = distance eye-pices; Piccoli spostamenti — small dis- 
placements; Disegno — drawing; Modello — Model; Scamotaggio triang. spaziale — com- 
mutation unit special triang; Pr. Amici = Amici prism; Interr. = switch. 
even at different scales, on cartographic tables placed even at a remark- 
able distance to each other, in the same room, or even in different rooms. 
In the following chapters is given a short description of the Photo- 
stereograph. In another paper it will be related about the pratical re- 
7