52 Proceedings of the Royal Irish Academy. 



The experiments described in this paper were performed with the same 

 method and the same style of apparatus as were used in the work on mercury. 

 Air was forced by a pump through a tine nozzle, placed a few cms. below the 

 surface of the alcohol. Before passing through the nozzle, the air was forced 

 through a cotton-wool plug. In none of the experiments was the air in any 

 way dried. A portion of the ionised air was then drawn off by means of a 

 gasometer through the cylindrical tube designed to measure mobilities. 

 The mobilities were determined by reading the current to the inner insulated 

 terminal fur various voltages on the outer tube, and thus plotting current- 

 voltage curves. These curves were Found to be similar to the curves obtained 

 in the previous work ; they were made up of a number of straight lines, 

 showing that dill'erenl types of ions were present. The mobilities of the 

 different kinds of ions were calculated from the formula 



u = ° a 



:'-n 



where Q is the volume of air passing through the tube per second, b and a 

 the radii of the tube and inner terminal, and / the length of the terminal. 

 T, the saturation voltage of a group of ions, is determined by the intersection 

 of two straight lines on the curve. Examples of these curves were given in 

 the List paper, BO it is not thought necessary to give any examples of the present 

 curves. The positive current is always practically the same as the negative 

 under the Bame conditions. In all the types of ions given below (with one 

 doubtful exception) the values ol the mobilities for the positive and negative 



ions are the - ime. Accordingly, listincti i sign has been made ; about 



half the observations refei to positive and half to negative ions. 



/' diminary • • 



The results of preliminary experiments on the determination of mobilities 

 are given in Table I 



