Condensation of Vapor As Induced By Nuclei And Ions Third Report

is variable with temperature in the region exam- ined to the extent of about 2 per cent per degree. The fog chamber used in the present research having undergone varied modifications since the coronas were last standardized 1904, it seemed necessary to repeat the work for the present report. This was particularly necessary because the subsequent investigations were to depend essentially on the values of the nucleation observed. These comparisons are shown in Chapters III and IV. In the former the diffractions are obtained from a single source of light and the angular diameter of the coronas is measured by a goniometer in the latter the fiducial annuli of two coronas due to identical sources of light are put in contact and the distance apart of the lamps is measured under known conditions. This contact method has many advantages and above all admits of the use of both eyes. In both cases, moreover, the nucleation of dust-free air, in the presence as well as in the absence of penetrating artificial radiation, is redetermined. All results agree among them- selves and with the older work, as closely as may be expected in work of the present kind, below the middle green-blue-purple corona usually corresponding to io5 nuclei but above this there is much divergence, which will probably not be overcome until some means for keeping the air rigorously homogeneous in nucleation throughout a given experiments has been devised. series of Chapter V contains some remarkable results on the properties of nuclei obtained from the evaporation of fog particles. It will be seen in that such residual water nuclei behave very differently, according as the precipitation takes place on solutional nuclei like those of phos- phorus, or upon the vapor nuclei of dust-free wet air, or upon the ions 80 per cent of the nuclei may vanish in the first evaporation in the latter case, fewer in the second case, and none in the first. In Chapter VI the endeavor is made to standardize the coronas by aid of the decay constants of the ions as found by the electrical method. The curious result follows that in order to make these data agree with those of Chapters III and IV it is necessary to assume an absorption of nuclei varying as the first power of their number as well as a decay by their mutual coalescence... --This text refers to an alternate Paperback edition.