Schermirhom, Analogue (Classical) Photogrammetric Instruments 
1 
of the moving space rod is avoided. In how far the movements of other mechanical 
elements introduce new sources of errors of a mechanical nature must be a subject of 
further research. 
Among the presented papers there is one by Prof. E. H. Thompson, giving a full 
description of the Thompson Watts Plotter Model II which, although announced at the 
London Congress, has only been in production during the last few years. The basic 
principle is still the same as that of the prototype published in “Photogrammetric 
Record” Vol. I, April 3rd, 1954, but a number of simplifications have been introduced 
which brings this instrument from the group of universal plotters into that of precision 
plotters. It can be considered an improvement, compared with the previous model. 
5. Topographic plotters. 
Regarding these we have to mention first that Wild has given to the Aviograph B9 
a greater range for principal distances with the result that in this instrument the same 
diapositives can be plotted as in the A9. This means that not only super-wide-angle 
photography but also wide-angle-photography reduced to half scale can be plotted 
without changing the support of the projectors. Furthermore it will be possible to connect 
a drawing table and the same pantograph system as used in the B8 to the B9. The result 
is that the use of this instrument needs not be restricted to small-scale restitution from 
super-wide-angle photography, but that it has exactly the same possibilities as in the 
Aviograph B8, naturally with the difference that the reduced size of the diapositive has 
some influence on the precision of the plotted result. 
We see in this class of instruments an important change of Galileo-Santoni Stereo- 
simplex II by creating the model IIC. The lower part with drawing table and panto 
graph is exactly the same as in the existing model IIB. Only the upper part with the 
support of the projectors has been changed and the plate-holders are mounted on a large 
circular bridge which allows the use of diapositives of the original size up to 9" X 9". 
The fact that reduction of the original photograph is no longer necessary must be 
considered as an improvement. The instrument has no 6?/-component of the base, but the 
circular bridges makes a common K possible. There is also no 6z-component of the base 
but instead of this there is the possibility for a common $ of the entire bridge. The 
required intersection of the space-rods in the model point is the centre of one gimbal 
joint. A change of the principal distance follows a system similar to that of the Stereo- 
Simplex III. 
Reprint from PHOTOGRAMMETRIA XIX, 1962-1964, No 4.