12 Proceedings of the Royal Irish Academy. 



These ions have not been all observed under the same conditions of experi- 

 ment. Some of the more mobile ions have only been obtained with dried 

 air, and a short interval between formation and measurement. Some of the 

 slower ions have only been found with uudried air, and a long time-interval. 



2. These ions are obtained with both positive and negative charges. The 

 numbers of positive and negative ions are always practically equal. 



3. The mobility of any group of ions does not change with time. 



4. With dried air the ions of higher mobilities become more prominent. 

 The values of the mobilities remain unchanged. 



5. Reasons are given for considering that the ions fomied by phosphorus 

 are mainly composed of water. 



