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been recently changed, for the spirit itself has no weight. 

 The departure or emission of spirit is rendered sensible in 

 the rust of metals, and other putrefactions of a like nature, 

 which stop before they arrive at the rudiments of life, which 

 belong to the third species of process. 67 In compact bodies 

 the spirit does not find pores and passages for its escape, 

 and is therefore obliged to force out, and drive before it, 

 the tangible parts also, which consequently protrude, whence 

 arises rust and the like. The contraction of the tangible 

 parts, occasioned by the emission of part of the spirit 

 (whence arises desiccation), is rendered sensible by the in 

 creased hardness of the substance, and still more by the 

 fissures, contractions, shrivelling, and folds of the bodies 

 thus produced. For the parts of wood split and contract, 

 skins become shrivelled, and not only that, but, if the 

 spirit be emitted suddenly by the heat of the fire, be 

 come so hastily contracted as to twist and roll them 

 selves up. 



On the contrary, when the spirit is retained, and yet ex 

 panded and excited by heat or the like (which happens in 

 solid and tenacious bodies), then the bodies are softened, 

 as in hot iron; or flow, as in metals; or melt, as in gums, 

 wax, and the like. The contrary effects of heat, therefore 

 (hardening some substances and melting others), are easily 

 reconciled, 88 because the spirit is emitted in the former, and 



67 Rust is now well known to be a chemical combination of oxygen with 

 the metal, and the metal when rusty acquires additional weight. His theory 

 as to the generation of animals, is deduced from the erroneous notion of the 

 possibility of spontaneous generation (as it was termed). See the next para 

 graph but one. 



68 &quot;Limus ut hie durescit, et hrec ut cera liquescit 

 Uno eodemque igni. &quot; Virg. Eel. viii. 



