A LABORATORY OPTICAL PYROMETER: 
NOTES ON ITS DESIGN AND OPERATION 
WM. SCHRIEVER 
The writer was confronted with the problem of measuring the 
temperature of a tungsten wire enclosed in an evacuated tube. A 
thermocouple could not be used because it would be certain to ap- 
ply unknown torques to the wire and also to disturb the tempera- 
ture distribution along the wire. An optical or radiation method 
of temperature measurement would overcome both of these diffi- 
culties. An optical pyrometer suitable for accurate temperature 
determinations and flexible enough to be of general use in a phys- 
ical laboratory is not on the market at the present time. This led 
the writer to the task of designing and constructing the instrument 
described in this article. For the benefit of those who are not fa- 
miliar with optical pyrometry a brief sketch of the theory and de- 
sign of a Holborn-Kurlbaum optical pyrometer has been included. 
GENERAL THEORY 
In figure 6 is shown a schematic diagram of a Morse or Hol- 
born-Kurlbaum type optical pyrometer.^ A is the background 
filament whose temperature is to be determined, B is a lens which 
forms a real image of A a,t D, C and B are limiting diaphragms, D 
Fig. 6. Schematic diagram of Holborn-Kurlbaum type optical pyrometer. 
is the pyrometer-lamp, F is a telescope focused on D and the image 
of yd, G is a monochromatic screen. In making a temperature de- 
termination the current thru D is adjusted so that the filament of 
D disappears against the image of A. Then the temperature is 
read from the current-temperature calibration curve of the py- 
rometer. 
The calibration of .the pyrometer is effected by replacing A by 
