Page 112 - My FlipBook

by the iiiilli-voltanictcr. When operated under certain conditions this
system is quite accurate. To operate it so that it is perfectly accurate,
the wires leading from the "thermo-couple" should be kept cold by arti-
ficial refrigeration. If these wires are permitted to heat up, the "thermo-
couple" loses in its efficiency to generate the same intensity of current.
One other point to bear in mind is the accuracy of the milli-voltameter
which must be so designed as to be extremely sensitive in registering

Fig. 122.

every minute variation of current change that takes place in the "thermo-
couple." It should be accurately adjusted or standarized at least once
a year.
The pyrometer designed by Mr. N. K. Garhart (Fig. 119) operates
on an entirely different principle from the "thermo-couple system." The
inventor took advantage of a special feature possessed by the "Nernst
glower," The "Nernst glower" is a miniature rod that is used for elec-
tric lighting and was confined to that use solely by its inventor, Mr.
Nernst. This element is made up of the oxids of the rare earths such as
are used in the manufacture of Welsbach gas mantels. These earths are
fused into two miniature rods which resemble fused porcelain in ap-

108