86 Lord Kelvin and Mr. M. Maclean. [May 31 r 



prevalence of negative electricity in the air, have been observed, 

 both indoors, in the large Bute Hall, and in many other smaller 

 rooms, and out-of-doors, in the court, which is somewhat similar to 

 the courts of the Old College, but much larger. It is possible that 

 the negative electricity found thirty years ago in the air of the Old 

 College, may have been due to its situation, surrounded by houses 

 with their fires, and smoking factory chimneys. In the New College 

 much of the prevalence of negative electricity in air within doors 

 has, however, been found to be due to electrification by the burning 

 lamp* used with the quadrant electrometer ; and more recent obser- 

 vations, with electrification by flame absolutely excluded, throw doubt 

 on the old conclusion, that both in town and country negative 

 electrification is the prevailing condition of natural atmospheric air 

 in the lower regions of the atmosphere. 



3. The electric ventilation found in the Old College, and de- 

 scribed in 299 of "Electrostatics and Magnetism," according to 

 which air drawn through a chink, less than ^ in. wide, of a slightly 

 open window or door, into a large room, showed the electrification 

 which it had on the other side of the chink, whether that was the 

 natural electrification of the open air, or positive or negative electri- 

 fication produced by aid of a spirit lamp and electric machine in an 

 adjoining room, has been tried again in the new College with quite 

 corresponding results. It has also been extended to the drawing in 

 of electrified air through a tube to the enclosure represented in fig. 1 

 of the present paper ; with the result that the water-dropping test 

 indicated in the sketch, amply sufficed to show the electrification, 

 and verify that it was always the same as that of the air outside. 

 When the tube was filled with loosely packed cotton-wool the electri- 

 fication of the entering air was so nearly annulled as to be insensible 

 to the test. 



4. The object proposed for the experiments described in the 

 present communication was to find if a small unchanged portion of 

 air could be electrified sufficiently to show its electrification by 

 ordinary tests, and could keep its electrification for any considerable 

 time ; and to test whether or not dust in the air is essential to what- 

 ever of electrification might be observed in such circumstances, or is 

 much concerned in it. 



5. The arrangement for the experiments is shown in the dia- 

 gram, Fig. 1. AA is a large sheet-iron vat inverted on a large 

 wooden tray BB, lined with lead. By filling the tray with water the 

 air is confined in the vat. There are two holes in the top of the vat ; 



* ' Electrification of Air by Combustion.' Magnus Maclean, M.A., F.R.S.E., and 

 Makita Goto, Philosophical Society of Glasgow, November 20, 1889 ; ' Electrifica- 

 tion of Air by Water Jet,' Magnus Maclean, M.A., F.R.S.E., and Makita Goto, 

 ' Philosophical Magazine,' August, 18CO. 



