t 



small heav^ Bodies in Air, Sec. 249 



vapour from the materials of combustion in ordinary fires. We 

 will now proceed to other phsenomena. 



Some few years past, in a very fine morning in the beginning 

 of October, between the hours of eight and nine, walking on 

 Richmond Green, I observed very long filaments of spiders 

 covering the grass, and advancing to the sun-dial placed on 

 the Green and surrounded with iron bars, I perceived several 

 of these filaments floating in the air from the pointed tops of all 

 the iron bars. On the top of every bar, I found spiders stand- 

 ing, from each of whom a filament passed, and, recollecting 

 Dr. Lister's observations on the flight of spiders by means of 

 their filaments, watched the animals, in expectation of seeing 

 them confirmed. I had not waited long before I saw a spider 

 throw himself from the spike, and ascend into the air, together 

 with, and attached to his filament floating above him. He 

 mounted until I lost sight of him at a height considerably 

 above the lofty elm trees which surrounded the green, and 

 over which he passed, by means of the gentle current of air in 

 which he floated. The pleasure and surprise of seeing this 

 exhibition was scarcely inferior to that with which I first con- 

 templated the ascent of a man in a balloon. In a very short 

 time many others took their departure, and continued to do so 

 whilst I stayed. More than once the floatage power not being 

 sufficient, the filament and its burthen came down again, and 

 the spider being received in my hand ran about upon it for a 

 short time, again took its departure, and was soon elevated 

 out of sight. Thus, the mode of conveyance of spiders was 

 completely confirmed in all its parts, and it only remained to 

 account for the phsenomenon by the first observers ascribed to 

 mechanical causes alone, but to be referred rather to the 

 general cases and causes of the floatage in air of vapours, of 

 particles of water, African sands, and volcanic dust, and intro- 

 duced here with its explanation by way of illustration and 

 confirmation of the doctrines advanced in the preceding pages. 



When water is dissolved in air, its particles are held in 

 solution by the attractions of the parts of the air on all sides 

 surrounding them, which are then strongest on every part of 



