of Air by Phosphorus. 479 



tubes, b, at each end, fitting over the rod and within the tube, 

 snugly. Thus the cylindrical shell (air-space) is but '141 

 centim. thick and 50 centims. long ; and the condenser is 

 adapted to bring to bear a high-potential gradient (the shell 

 of air being as thin as admissible in consideration of flexure) 

 along a considerable length of air-column conveying phos- 

 phorus nuclei. The outside of the condenser (fig. 1) is per- 

 manently put to earth, while the rod inside is in metallic 

 connexion with the electrometer-needle, as suggested in the 

 figure at E. A suitable key is added in order to conveniently 

 charge the rod. Upwards of 300 volts were applied. Not- 

 withstanding its slender dimensions, no difficulty attends the 

 use of the condenser. 



The air from a gasometer-train, after passing the desiccator 

 D, and the stopcock F, is charged with nuclei by the 

 ionizer, P, containing pellets of phosphorus between strips of 

 wire-gauze. It then traverses the condenser L K, and thence 

 enters the colour-tube- The gasometer has already been 

 described in the preceding papers of the present series. 



3. The method of observation was as follows : — The two 

 sets of data to be obtained, namely the readings at the volume- 

 fia^k and at the electrometer, were taken in consecutive 

 minutes, the stopcock F having been previously adjusted to 

 show any desired colour in the steam-tube. From obser- 

 vations at 15 seconds apart at the gasometer, I obtained two 

 sets of results for the discharge of air per second, the pressure 

 of the jet (p), the temperature of the inflowing air (#, by the 

 thermometer T in the figure), the pressure of the air in the 

 gasometer, and its temperature. 



Meanwhile the condenser had been charged to its full 

 potential, and after breaking the charging- circuit the leakage 

 of the electrometer was observed each 15 seconds. This 

 furnished two sets of data for the initial electric current. 



4. The experiments with the train of apparatus described 

 usually progressed smoothly. The data of two out of four 

 similar series are given in Table I., which is divided into three 

 parts, referring respectively to the steam -jet, the gasometer 

 (volume conveyed per minute, V being the essential datum), 

 and the electrometer. It was thought superfluous to reduce 

 the air-volumes to normal conditions, as the fluctuation of 

 pressure (pressure-excess, p) and temperature [0) are rela- 

 tively insignificant in view of the variability of the ionizer. 

 For the steam-jet the pressure, p, and temperature, #, are also 

 practically constant. Relatively to the electrometer series, 

 the two initial potential-differences, E, are given as obtained 

 immediately alter, and 15 seconds after charging. These are 



