This is what Professors Lummer and Pringsheim have shown in a series
of studies which may certainly be reckoned among the greatest
experimental researches of the last few years. They have constructed a
radiator closely resembling the theoretically integral radiator which
a closed isothermal vessel would be, and with only a very small
opening, which allows us to collect from outside the radiations which
are in equilibrium with the interior. This vessel is formed of a
hollow carbon cylinder, heated by a current of high intensity; the
radiations are studied by means of a bolometer, the disposition of
which varies with the nature of the experiments.
It is hardly possible to enter into the details of the method, but the
result sufficiently indicates its importance. It is now possible,
thanks to their researches, to estimate a temperature of 2000 deg. C. to
within about 5 deg. Ten years ago a similar approximation could hardly
have been arrived at for a temperature of 1000 deg. C.
Sec. 6. DERIVED UNITS AND THE MEASURE OF A QUANTITY OF ENERGY
It must be understood that it is only by arbitrary convention that a
dependency is established between a derived unit and the fundamental
units.
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