484 Electrification of Air, Vapour of Water, and other Gases. 



§ 2. The method for testing the electrification of air which was 

 nsed in their earliest experiments was an application of the water- 

 dropper,* long well known in the ordinary observation of atmo- 

 spheric electricity. Its nse by Maclean and Gotof in 1890 led to 

 an interesting discovery, that air in an enclosed vessel, previously 

 non- electrified, becomes electrified by a jet of water falling through 

 it. An investigation of properties of matter concerned in this effect, 

 related as it is to the " development of electricity in the breaking 

 up of a liquid into drops " which had been discovered by Holmgren % 

 as early as 1873, and to the later investigations and discoveries 

 described by Lenard,§ in his paper on the " Electricity of Water- 

 falls," forms the subject of §§ 25 — 37 of the present communication. 



§ 3. The electrification of air by drops of water, breaking from a 

 jet in it, or falling through it, or striking on the ground, or on 

 water, or on metal below it, produces absolutely no practical disturb- 

 ance of the electric potential measured by the water-dropper in its 

 use for the observation of open air atmospheric electricity : but con- 

 stitutes a serious objection to its application for investigating 

 atmospheric electricity within doors, unless in a very large room 

 or hall, and renders it altogether unsuitable for experimental investi- 

 gations, such as those described in the present paper. 



§ 4. The authors were, therefore, early led to abandon it: and, 

 for testing the electrification of air, they used three different 

 methods, one or other of which they found convenient in different 

 cases. 



Method 1. Observation of electrification of the substance receiving 



the electricity equal and opposite to that taken by air in any 



case of electrification of air. 

 Method 2. Observation of the electricity of an insulated metal vessel 



into which electrified air is introduced, or from which electrified 



air is removed. 



" On the Diselectrification of Air," by Loud Kelvin, Magnus Maclean, and Alex- 

 ander Gait, ' Roy. Soc. Proc.,' March, 1895 ; " On the Electrification of Air," by 

 Lord Kelvin, ' Glasgow Phil. Soc. Proc.,' March, 1895 ; " On the Electrification 

 and Diselectrification of Air and other Gases," by Lord Kelvin, Magnus Maclean, 

 and Alexander Gait, ' Brit. Assoc. Report,' 1895, p. 630. 



* Kelvin and Maclean, ; Roy. Soc. Proc.,' 1894, and Kelvin, Maclean, and Gait, 

 ' Roy. Soc. Proc.,' February, 1895 ; ' Electrostatics and Magnetism,' § 262 (from 

 ' Lit. and Phil. Soc. of Manchester Proc.,' October 18, 1859). 



f " Electrification of Air by Water- jet," by Magnus Maclean and Makita Goto, 

 « Phil. Mag.,' August, 1890. 



% " Sur le Developpement d'Electricite a l'occasion de la Dissolution en Gouttes 

 des Liquides," ' Kongl. Sv. Yet. Ak. Handl.,' vol. 11, Jfo. 8, pp. 14—43 (pour l'an 

 1873). 



§ "Ueber die Electricitat der Wasserfalle," by P. Lenard, ' Annalen der Physik 

 und Chemie,' 1892. 



