The mobility‐spectrum of atmospheric ions—principles of measurements and results

Abstract

In the first part of the work, the methods of determining the “ionic spectrum,” that is, the percentage‐distribution of the ions for different mobilities, are discussed. The principle of the measurements consists in obtaining a current‐potential characteristic of a condenser through which air containing ions is passed. The ionic spectrum is obtained by forming a second differential quotient of the characteristic. Three different methods are described and their “resolving‐power” is discussed: The double‐condenser method, the method of the subdivided condenser, and the analysis according to Benndorf. In the second part the ionic spectra as determined to date at twelve different stations are assembled. Since the revolving‐power of the double‐condenser method is limited, only four rather large mobility‐regions are at present differentiated. Apart from very large local differences, which cannot yet be cleared up individually, there appears an annual variation in the composition of the spectra, such that the spectral center of gravity lies at the smaller mobilities in winter and at the larger in summer. Increase of humidity has obviously the effect of enlarging the ions or of diminishing their mobility through the accretion of water‐vapor by them. A consideration of the separate representative mobilities of the various spectra shows that these are related as 1 : 2 : 3 or 1 : 2 : 4. This simple relationship suggests that perhaps the ions are of equal size but with one, two, or more elementary charges.