VOL. XLII.] PHILOSOPHICAL TRANSACTIONS. 547 



a room in the air, and does not attract it a second time, till the feather has 

 touched some other body ; and also shows the reason why the experiment does 

 not succeed in moist weather. 



Pure air, that is dry, may be ranked among the electrics per se, because it 

 repels all bodies in a state of electricity, whether they have been excited to it 

 by wax or glass ; that is, by either of the two sorts of electricity. 



Watery vapours, that float in the air, are non-electric ; from which mixture 

 the air becomes more languid in its electricity, when most impregnated with 

 vapours ; so that dry air is more electric than moist ; but cold air in frosty 

 weather, when vapours rise least of all, is more electric than air in summer, 

 when the heat raises vapours ; which renders that state of the air more fit for 

 making electrical experiments. 



The rubbed tube retains its electricity a long time, because it repels, and is 

 repelled by, the dry air ; and the feather, which has been attracted by the tube, 

 after adhering to it a while, is raised out of its languid state to a strong electri- 

 city ; by which it flies from the tube, repels and is repelled by the air, where 

 meeting with very few vapours, it retains its electricity a long time ; till touch- 

 ing a non-electric, that is brought to it, it loses its own electricity by com- 

 municating it, becomes a non-electric, and is re-attracted by the tube, to which 

 adhering some time, it receives so much virtue from the tube, as to be restored 

 to its electricity, and again repelled. 



In a moist state of the air, the feather, after it has been made electrical, and 

 repelled by the tube, it attracts to it the moist vapours floating in the air ; by 

 which losing its electricity, it is attracted by the tube, without touciiing any 

 other body first. 



Sometimes, when the feather flies off^ from one part of the tube, it immedi- 

 ately returns to another part, generally the top of the tube, because the top of 

 the tube has attracted the moist vapours, and is become a non-electric, and 

 therefore attracts the feather ; which having become electric, flew ofi^ from the 

 electric part of the tube. 



That this is true, appears from an experiment to be made in dry weather. At 

 that time, when every part of the tube repels the feather, strongly, after having 

 attracted it, if you wet 2 or 3 inches of the upper end of the tube, the feather 

 will come to that end. Wetting the silk by which the feather hangs from the 

 cat-gut, the feather will be always attracted, and not repelled. 



When the silk is dry, the feather once made electrical, so as to be repelled 

 by the tube, retained that virtue above 2 hours in frosty weather ; but in moist 

 weather lost it in half a minute. 



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