98 ESSAYS AND OBSERVATIONS 



contact. But if this cafe afford not an 

 ihflance of attraclion being converted in- 

 to repulfion, it affords an inflance of a 

 change not lefs extraordinary, 'viz. a repul- 

 fion confined within a very fmall fphere 

 of atftivity, converted into a repulfion ha- 

 ving a very large fphere. It is obferved 

 above, that heat increafes the force ofe- 

 ledive attraction ; and here I have occa- 

 lion to obferve, that it has the fame effect 

 with refpedl to eledlive repulfion. Heat, 

 by increafing the repulfive power of the 

 particles of water, expands it to a great- 

 er bulk, perhaps about ^j, more or lef& 

 in proportion to the degree of heat under 

 that of boiling water. But, as foon as 

 the water begins to boil, the mutual re- 

 pulfion is increafed to fuch a degree as to 

 convert the furface of the water into va- 

 pour, which is water expanded 14,000 

 times beyond its ufual flate. And accor- 

 dingly, tho', during the inferior degrees 

 of heat, there is little evaporation j yet, 

 when water boils, vapour is thrown up 

 in great plenty. 



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