70 



that multiplicity of ferments, meteors, tempests, and 

 all the other changes in it, which we experience. 

 They were acquainted too with its weight, though 

 the experiments transmitted to us relative to this are 

 but fr-w. Aristotle appears to have observed th:S 

 quality in it, lor he Speaks 6 of a vessel filled with air, 

 as webbing more than one quite empty.' - Flu* 

 tarch and Stubaeus quote him as teaching that the * air 

 in its weight is between that of fire, and of earth ;* 

 arid he himself, treating of respiration, rrpor's the 

 opinion of Empedocles, who ascribes the cause of it 

 * to the weight of the air, which by its pressure in. 

 sinuates itself with force into the lungs. Plutarch ex. 

 presses in the very same terms the sentiments of As- 

 clepiadt-s on this subject, representing him among 

 other things, as saying, that ' the external air by its 

 weight, opered its way with force into the breast** 

 There is stil extant a treatise of Heron of Alexan- 

 dria, wherein heconstantly applies the elasticity of the 

 air, to produce such effects, as cannot but coii?ince 

 us, that he perfectly understood that property of it. 

 And what will appear still more surprising, is, that 

 Ctesibius, * upon tjie principle of the air's elasticity/ 

 invented wind. guns, which we lock upon as a modern 

 contrivance. Fbilo of Byzantium gives us a very full 

 and exact description of that curious machine, planned 

 ii} on the property of the air's being capable of con. 

 densation, and so constructed, as to manage and di- 

 rect the torce o< that element, in such a manner, as 

 to carry stones with rapidity to the greatest distance. 

 Seneca also knew its weight, .spring, and elasticity ; 

 for he describes * the constant effort it makes to ex- 

 pand itself, when it is impressed ;' and * affirms that it 

 has the property of condensing itself, and forcing its 

 way through all obstacles that oppose its passage.' 



6. The notions most generally received respecting 

 fire, and its prupntits, are clearly to be found iu 

 PHI , S < baeos, Aristotle and L cretins ; <he first of 

 wuom bays, thai fire is ^cuuau-u of uiouon, it being 



