Guardian._

* * * * *




SEYFFERTH'S PYROMETER.


The thermometers and pyrometers usually employed are almost all based on
the expansion of some fluid or other, or upon that of different metals.
The first can only be constructed with glass tubes, thus rendering them
fragile. The second are often wanting in exactness, because of the
change that the molecules of a solid body undergo through heat, thus
preventing them from returning to exactly their first position on
cooling.

[Illustration: Fig. 1.--Pyrometer with Electric Indicator.]

The principle of the Seyfferth pyrometer is based on the fact that
the pressure of saturated vapors, that is, vapors which remain in
communication with the liquid which has produced them, preserves a
constant ratio with the temperature of such liquid, while, on the other
hand, the temperature of the latter when shut up in a vessel will
correspond exactly with that of the medium into which it is introduced.

[Illustration: Fig. 2.--Method of Mounting by means of a cone on vacuum
apparatus.]