ept at a constant temperature by the
water bath. When the temperatures of the two junctions are the same, the
system is in equilibrium. When they are at different temperatures, an
electrical potential is set up, which causes a current to flow from one
to the other through the galvanometer. The galvanometer consists of a
magnet set up inside coils through which the current I spoke of flows.
This current causes the magnet to rotate and by watching the mirror, the
rotation can be detected and measured.

"This device is one of the most sensitive ever made, and is used to
measure the radiation from distant stars. Currents as small as
.000000000000000000000000001 ampere have been detected and measured.
This particular instrument is not that sensitive to begin with, and has
its sensitivity further reduced by having a high resistance in one of
the leads."

"What are you going to use it for?"

"I am going to try to locate somewhere in these hills a patch of local
cold. It may not work, but I have hopes. If you will manipulate the
telescope so as to search the hills around here, I will watch the
galvanometer."

* * * * *

For several minutes Carnes swung the telescope around. Twice Dr. Bird
stopped him and decreased the sensitiveness of his instrument by
introducing more resistance in the lines in order to keep the magnet
from twisting clear around, due to the fluctuations in the heats
received on account of the varying conditions of reflection. As Carnes
swung the telescope again the magnet swung around sharply, nearly to a
right angle to its former position.

"Stop!" cried the doctor. "Read your azimuth."

Carnes read the compass bearing on the protractor attached to the frame
which supported the telescope. Dr. Bird took a pair of binoculars and
looked long and earnestly in the indicated direction. With a sigh he
laid down the glasses.

"I can't see a thing, Carnesy," he said. "We'll have to move over to the
next crest and make a new set-up. Plant a rod on the hill so that we can
get an azimuth bearing and get the airline distance with a range
finder."

On the hilltop which Dr. Bird had pointed out the apparatus was again
set up. For several minutes Carnes swept the hills before an exclamation
from the doctor told him to pause. He read the new azimuth, and the
doctor laid off the two readings on a sheet of paper with a protractor
and made a few calculations.

"I don't know," he said