The new North-west. [volume] (Deer Lodge, Mont.) 1869-1897, 1880-12-17
THERMAL BALANCE.
An Instrument Invented BY Prof g. p. Langley
Of the Allegheny Observatory.
pittSburp Chronicle.

Pittsburg Chronicle.
h Before the National Academy of Sciences,
In session at New York, Prof. s. p. Langley,
Of the Allegheny Observatory, read two in
teresting papers. One was on the "Thermal
Balance" and the other on Measurement
Of Radiant Energy" In order to measure
the distribution of fadiant energy in pure
spectrum, when the rays have not passed
through prism, Professor Langley was
obliged to invent more sensitive recording
instrument than the thermopile, which Is
generally used for delicate observation OF ra-
diant heat. The apparatus Is founded on
the principle that If wire conveying an
electric current be heated less electricity
flows through it than before. H @- "
The application of this principle Is thus
made: Iron or steel Is rolled into sheets OF
extreme thinness. The speaker said he
had succeeded in rolling sheets Of steel
made at the works of Miller g. Parkins, ut
Pittsburg, until 1t took 5000 OF them to
make the thickness of an inch. Specimens
Of these sheets were exhibited, together with
platina, rolled at the United States mint in
Philadelphia, even thinner. Of these sheets
fifty laid one upon the other did not equal
the thickness of thin tissue paper. Minute
strips 1872 Of an inch wide and Of an Inch
long, cut from this were united 80 as to form
q prominent part of the circuit, through
which current of powerful battery passed
to the galvanometer. Experiment proved
that an almost inconceivable minute warm
ing of set of these strips would reduce the
passage of the electricity so as to produce
very large indications on the registering in
strument. Professor Langley had, In the
course of his experiments thus far. he said,
found iron the most advantageous, though
other metals were still under trial. The in
strument thus formed was from ten to thirty
times more sensitive than the most delicate
thermopile, but this was almost secondary
advantage compared with its great precision,
and the readiness with whichit Is compared.
The thermopiie Is very slow in Its action.
This new instrument, the thermal-balance,
takes up the heat and parts with 1t again in
single second. 1t is almost as prompt as
the human eye itself.
To show its accuracy, Professor Langley
gave experiments which proved that the
probable error of single measurement
made with the instrument could DO reduced
within one per cent. of the amount to be
measured. To show It's sensitiveness, the
statement was made that II would register
change in temperature Of the iron strips
just described which did not exceed 80
600 part of Fahrenheit degree. When
mounted in rejecting telescope 1t would
record the heat Of nan or other animal In
distant field. It would do this equally
we'll in the night, and might be said, in q
certain sense, to give the power of seeing in
the dark. A more valuable proof Of Its efii-
cheney was shown in series Of measure
ments OF the heat Of the moon, made under
varied circumstances, to guard against error,
but each made in few seconds. All agreed
in showing that the almost iinmeasurably
minute amount Of heal from the moon could
be certainly measured by 1t, even with o
common refracting telescope. ..t