Cluster in a Gas under Influence of an Electric Field. 919 



produce further ions by collision. This method was previously 

 employed to study the properties of negative and positive 

 elementary ions and clusters *. The same apparatus was 

 used in these experiments, a full description of which will be 

 found in the last paper quoted. A brief description only 

 will be given here. The ionization chamber consisted of a 

 cylindrical chamber, of which a vertical section passing- 

 through its axis is shown in fig. 1. A wire gauze B was in 

 electrical connexion with the chamber and situated at a 



distance of *5 or 1 cm. from the 

 circular plate A. The rod to which 

 the plate is attached was insulated 

 from the chamber in the usual 

 way, and in electrical connexion 

 with an electrometer. The por- 

 tion a of the gas in the chamber 

 on the lower side of the gauze was 

 ionized by the a particles from a 

 suitably arranged layer of ura- 

 nium oxide. On connecting the 

 chamber with a negative or posi- 

 tive potential, negative or positive 

 ions were respectively drawn by 

 the comparatively weak field exist- 

 ing between gauze and chamber- 

 wall into the much stronger field existing between gauze 

 and plate. The field between gauze and plate was usually 

 gradually increased till of such strength that further ions 

 were produced in considerable quantities by the collision 

 of the free ions with neutral molecules. Some of the ion 

 clusters become elementary ions in the way just described on 

 their passage from gauze to plate. These would at once be 

 seized upon by the electric field and assist in the production 

 of further ions by collision. Therefore on measuring the 

 current between gauze and plate for electric fields of different 

 strengths, information on the behaviour of ion clusters under 

 the action of an electric field may be obtained. 



In this paper the results will be described obtained by 

 drawing negative ions through the gauze and measuring the 

 leaks for different fields up to fields of intensity when 

 ionization by collision with positive ions should come in. 

 The investigation is thus a continuation of that described in 



* Proc. Camb. Phil. Soc. vol. xvii. pt. iii. p. 203 ; ibid, vol. xvi. pt. viu 

 p. 621. 



3P2 



