The Indianapolis times. [volume] (Indianapolis [Ind.]) 1922-1965, 1933-03-29
.Dietz on Science
-Dietz on Science
SUMS HEAT is
MEASURED BY
DELICATE DISK
Years of Experimenting
Required to Perfect
instrument.
BY DAVID DIETZ
Scripps Howard Science Editor

Perfection Of the silver-disk pyr-
heliometer has been one CT the tri-
jumps of the thirty-year study Of the
suns radiation, conducted by the
Smithsonian Institution under the
direction of DR.. G. G. Abbot III an
attempt TO find the connection be-
tween solar activity and the weather.
1t was in 1902 that Dr. Abbot first
undertook to measure the solar con-
slant, that is, the amount Of heat
and light received from the sun
per unit area. There was in exist
ence at that time several pyrhelio-
meters, as instruments for this pur-
pose are known to scientists.
One was an electrical device de-
signed by Knut Angstrom. The
other was an older and simpler de-
vice, the work of Pouillet and Tyn-
dali.
Pointed at Sun
DR.. Abbot chose to work with the
simpler device and made changes
and Improvements, which culmin-
ated in 1910 in the silver-disk pyr-
hehOmeter. Since that year more
than seventy standardized copies of
this instrument have been made at
the Smithsonian Institution and
furnished to observatories in all
parts of the world
The instrument consists of a small
tube, open at the upper end which
is pointed toward the sun At the
lower end is a blaCkened silver disk
which contains a tiny reservoir Of
water A thermometer bulb is i'm
merSed in the reservoir.
The solar constant is calculated by
observing the rate at which the
thermometer rises when the tube is
pointed at the sun.
The silver disk pyrheliometer
however, can only be used after it
has been standardized or calibrated
Means are required for reducing the
reading of the thermometer which
is in degrees, to true calories per
square centimeter per minute.
Devises Two instruments
A calorie, it will be recalled, is the
amount of heat necessary to raise
the temperature of a cubic cent?
meter of water one degree. cent?
grade.
DR.. Abbot devised two instruments
for standardizing purposes known as
the water-flow pyrhehometer and the
Water-Stir pyrheliOmeter.
IN the standard Water-foW pyr-
heliometer," DR.. Abbot explains. the
solar rays admitted by measured
aperture are chiefly absorbed on a
hollow, blackened metallic come at
the rear of test-tube- shaped
blackened metallic chamber.
"A measured current of water
continually removes the heat pro-
duced on the cone and on the inner
walls of the chamber. An electrical
thermometer measures the rise of
temperature thus produced in the
water current"
Accuracy Is Satisfactory
For test purposes, DR.. Abbot adds.
known quantities of heat may be in
troduced at the cone in the stand
ard water-flow pyrheliometer by
measured electrical currents.
The accuracy of the instrument,
which is very satisfactory, is
measured by the equivalence of heat
introduced and heat found" he says.
Within the last year, DR.. Abbot
has perfected a still more accurate
Standardizing instrument which is
known as the double water-flow
pyrheliometer. The accuracy of this
new form of the instrument is be-
lieved to be better than tenth
of ! per cent.