Although it is easy to detect and measure the bursts of cosmic-ray ionization, or Hoffmann St6sse, by means of vacuum tube electrometers 1 or electroscopes/such arrangements are inconvenient to employ in field work since they require quite steady supports and relative freedom from vibration, as well as a degree of constancy of the potential sources not easily attainable. An arrangement which minimizes these difficulties is here described. The change in potential of the collecting electrode of the ionization chamber in which the burst occurs is amplified by a degenerative, directly-coupled vacuum tube amplifier, and the output pulse from this amplifier is applied to a "magic eye" indicator tube. This indicator tube acts as a cathode-ray oscillograph, and is directly photographed on continuously moving sensitive paper to give a record of the burst.
To achieve an amplification of a thousand-fold and at the same time have the action of the amplifier independent of changes in battery potential, temperature, and so forth, a directly coupled amplifier was employed, with a large negative feedback. Suppose we have an amplifier of gain g without feedback working into a resistance R, and suppose that a portion of this resistance is used to feed back the pulse to the input, then it is easy to show that the resultant gain, G, is given by R/r~I + (R + r)/rg~. Now if g is large "compared to R/r, the quantity in brackets in this expression becomes almost unity. The gain G is then determined only by the values of the resistances, and is independent of g. This re-