188 LORD KELVIN, DR. M. MACLEAN, AND MR. A. GALT, ON THE 



described by LKNARD,* in his paper on the " Electricity of Waterfalls," 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 disturbance 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 the experimental investigations with which we are now concerned. 



4. We were, therefore, early led to abandon it ; and, for testing the electrifica- 

 tion of nil-, we have used three different methods, one or other of which we have 

 found convenient in different cases. 



Method (l). 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 a hollow metal vessel into which 

 electrified air is introduced, or from which electrified air is removed. 



Method (3). Observation of the electricity taken out of air by the electric filter ( 9). 



5. Method (l) was used in the experiments described in our communication to 

 the Royal Society of February, 1895, from which we concluded that air, and several 

 other gases tried, became electrified by blowing them in bubbles through water, and 

 through solutions of various salts, a,cids, and alkalies in water. We verified this 

 conclusion, for the case of common air and pure water, by collecting into a large 

 reservoir over water, air which had been bubbled through pure water in a U-tube. 

 We tested the electrification of the air thus collected by a water-dropper taking the 

 same potential as the air at the centre of the reservoir. We thus proved that the 

 electrification of the air was negative, as was to be expected from the positive 

 electrification which we had found on insulated vessels containing water through 

 which air had been bubbled. 



6. Method (2) was used in the first experiments described in the present paper 

 ( 16-24), which were undertaken for the purpose of determining approximately in 

 absolute measure the total quantity of electricity in a given mass of electrified air, 

 and particularly for finding the greatest electrification which we could communicate 

 to a large quantity of air by needle points supplied with electricity from an electric 

 machine. The result thus found in 23 below, 37 X 10~* C.G.S. electrostatic, is 

 the gi-eatest electric density (quantity of electricity per cubic centim.) which we 

 have been able to communicate to air by electrified needle points. But, by an 

 electrified hydrogen flame a density of 22 X 10"* C.G.S. electrostatic unit was 

 obtained ( 65). 



7. In all the experiments described in our paper after 24, method (3) was 

 used ; but, probably, we must return to method (2) if, in future, we undertake 



* " Ueber die Electricitat der Wasserfalle." By P. L.ENAKD, ' Annalen der Physik und Chemie,' 1892, 



