centre, is slid over the coaxial bolt 2 and securely clamped so that the template 
follows the rotation of the disk without slipping. The cutter carriage 4 which 
accommodates cutter 3 and the matrix support may be displaced parallel to 2—3 
in guide 5. The displacement is controlled by handwheel 6. However, it is not 
performed directly but through guide 7 of the spotting microscope 8. 
An adjusting lever which pivots about 9 connects the microscope holder at 
10 with pilot guide 11 of the cutter carriage. It becomes immediately evident that 
the motion imparted by handwheel 6 to the microscope is transmitted to the cutter 
carriage in the ratio of the distances gru" The value of this ratio, which is equal 
to the ratio of the desired triangulation scale to the given image scale, can be set 
on scale 12 by displacing guide 1. The image points are observed over mirror 13 
through microscope 8 and are set in azimuth by turning the large disk by hand. 
The large size of the exit pupil prevents eye strain and permits a convenient posture 
of the operator's head. 
If the value and direction of the picture tilt are known and it is desired to 
correct the angular distortions 
‘ * y . 
à = sm = . sin 2a 
(where » is the tilt of the photograph and a the angle formed by the direction 
to be corrected and the line of intersection of picture plane and horizontal plane) 
eccentric lever 14 is operated. The value of » is set on a division of eccentric disk 
15 which is rotated by a drive according to 2a. The division is provided with 
numerals according to picture tilt ». The lever, which pivots about 16, then 
performs the angular motions ó. With its free end it displaces the spotting micros- 
cope by an azimuthal value corresponding to the value of ó and the distance from 
the radial point. The operator does not notice any of these corrections; the power 
required for punching the radial slots is transmitted from a pedal to the cutter at 17. 
Templates with a maximum diameter of 480 mm may be processed. Another 
feature worth mentioning is the novel way of fastening the paper prints upon 
the photocarrier disk. The metal clips which were used formerly have been replaced 
by small, powerful permanent magnets which can be placed anywhere on the 
picture and which press it securely against the iron disk by the inherent magnetism. 
III. ,,Stereotop” Mirror Stereoscope Equipment. 
The mirror stereoscope and the observation and plotting instruments derived 
from it, which are nowadays commonly known as ,,3rd order plotting instruments”, 
have come to occupy a permanent place in photogrammetric practice. A large 
number of different models are on the market. The preference of inventors for 
simple instruments of this nature produces new variations all the time, and some 
of them are manufactured more or less successfully. Obviously, immense areas 
are being currently mapped on medium and small scales with the aid of these in- 
struments. : 
Apart from their application for topographic and cartographic work proper, 3rd 
order instruments help evaluate the wealth of surface details and information sup- 
plied by aerial photographs. With the aid of geologic practice and methods of 
evaluation, this information can also be made available for the exploration of the 
8