IV PREFACE. 



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. If a be the number of nuclei (ions) gen- 

 erated per second by the radiation, b the number decaying per second, 

 and c the number absorbed per second, the equation dn/dt a + bn^ + cn 

 is suggested. 



My thanks are due to Miss L. B. Joslin, who not only assisted me in 

 many of the experiments requiring two observers, but lent me efficient 

 aid in preparing the manuscripts and drawings for the press. 



CARL BARUS. 



BROWN UNIVERSITY, July, 1907. 



