1888 - 89 .] Sir W. Thomson on Electrification of Air. 
263 
having its nozzle at the centre of the room and about 7 feet above 
the floor, was always found about 2 volts negative at the commence- 
ment of the observations, and always increased to about 9 volts in 
the course of the first twenty minutes of a series of observations last- 
ing generally forty minutes. During the last twenty minutes of the 
series the potential remained somewhat nearly constant at 9 volts. 
Within the room, two quadrant electrometers, each with an ordin- 
ary paraffin lamp and scale, were used ; one of them for the outside 
water-dropper, and the other for the water-dropper within the room. 
Towards ascertaining the cause of this change, an observation was 
made on the 4th July, between 10 and 11 a.m. The lamps were 
both extinguished, and one of them was lighted by a lucifer match 
every five minutes for the purpose of reading the electrometer de- 
flection. It was found that in these circumstances there was not 
the increase of negative potential which had been found in every 
previous series of observations in the same place, and with all other 
circumstances the same, except the burning of the lamp. This 
single observation seemed to prove conclusively that the burning of 
the lamp produced a negative change of the air of the room. Subse- 
quent experiments made by Mr Goto, with the electrometer and its 
lamp and scale outside, and with paraffin lamps burning or not 
burning within the room, have confirmed this result, and are being 
continued to discover whether corresponding effects are produced 
by other kinds of flame, or by the presence of eight or nine people 
in the room. Mr Maclean and Mr Goto will also continue their 
observations on natural atmospheric electricity, in various localities, 
indoors and in the open air, and will, I hope, give a paper to 
the Royal Society of Edinburgh early next session on the 
subject. 
