LABORATORY OPTICAL PYROMETER 
77 
The telescope H was obtained from Wm. Gaertner. The ob- 
jective lens of this telescope is 30 mm. in diameter and it has a 
focal length of about 25 cm. It is furnished with two eyepieces, 
one of 18 mm. and one of 25 mm. focal length. The shorter focal 
length eyepiece is to be used with fine pyrometer-lamp filaments. 
In the lens-cap is a 15 mm. hole, the edges of which are beveled on 
the inside. This serves as the diaphragm B of figure 6 for the lower 
temperatures. At medium and high temperatures this stop is too 
large, hence three brass discs, which fit snugly in the cap are 
provided. These have apertures of 13 mm., 10 mm., and 8 mm., 
respectively. The disk having the 13 mm. hole proved to be the 
most useful one for the setting shown in figure 7. 
Two pieces of red glass, each 1 .cm. in diameter and 5 mm. 
thick, mounted in brass housing, form the monochromatic screen, 
G Fig. 6. The effective- wavelength of this screen, between 1200 
and 2400° K, is 0.658 micron. The colored glasses together with 
effective- wavelength calibration data were obtained from the Nela 
Research Laboratory of the General Electric Company, Nela Park, 
Cleveland. The brass housing is equipped with three spring-brass 
fingers which hold it in place on the eyepiece of the telescope. The 
black cardboard shade I keeps light, other than that coming 
' through the telescope, from entering the operator’s eyes. It en- 
ables the observer to keep both eyes open, thus making the obser- 
vation less tiresome. 
Telescoping- tube standards allow the objective lens and the tel- 
escope to be adjusted vertically and to be rotated about vertical 
axes. The telescope rests in the two V-shaped pieces of an ordi- 
nary laboratory telescope-clamp. In each arm of the rear ‘V’ is 
a thumbscrew. These thumbscrews make possible the small ad- 
justments which are usually necessary to bring the axis of the tele- 
scope in coincidence with the optical axis of the pyrometer. 
The pyrometer-lamp is mounted on the standard shown at D in 
figure 7. It is inside of the black cylindrical tube which prevents 
reflection of light from the outside of the lamp-bulb. Figure 8 
shows the standard more in detail. The white porcelain lamp- 
socket is screwed to a round brass disc which is held in a recess 
in the square base-plate by two spring clips ; this permits the lamp 
to be turned about its axis until the filament is perpendicular to the 
optical axis of the pyrometer. The square base-plate is fastened to 
a ring R which slides on another ring N to which it is held by two 
spring clips. The ring N stands on a plate which can be moved 
horizontally by turning the knurled head B. The rings make it 
