"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 reflectively when he had finished his computations. "This darned instrument is still so sensitive that you may have merely focused on a deep shadow or a cold spring or something of that sort, but the magnet kicked clear around and it may mean that we have located what we are looking for. It should be about two miles away and almost due west of here." "There is no spring that I know of, Doc, and I think I know of every water hole in this country," remarked Bill. "There could hardly be a spring at this elevation, anyway," replied the doctor. "Maybe it is what we are seeking. We'll start out in that direction, anyway. Bill, you had better take the lead, for you know the country. Spread out a little so that we won't be too bunched if anything happens." * * * * *