4(» ANSWERS to the OBJECTIONS 



fible. I then fay, That this cafe properly applies to the pheno- 

 mena of breath and fteam, which give a vifible condenfation in 

 mixing with the colder atmofphere ; and it explains the various 

 appearances that may occur in mixing together feveral portions 

 of air more or lefs faturated with humidity, and in different 

 temperatures of heat and cold. For, 



It is not every mixture of the atmofpheric fluid, in different 

 temperatures, that fhould, according to the theory, form a vifi- 

 ble condenfation ; this effecfl requiring, in that atmofphere, a 

 fuiEcient degree offaturation with humidity. Neither is it ne- 

 ceffary for this effed, that the two portions to be mixed (hould 

 each be faturated with humidity up to the temperature in 

 which it then is found ; it is fufficient, that die difference in the 

 temperatures of thofe portions to be mixed fliould more than 

 compenfate the defedl in point of faturation ; but if a mixture 

 fliall be made of two portions of the atmofphere, both fully fa- 

 turated with humidity, then, however fmall may be the differ- 

 ence of their temperatures, there is reafon to believe, that a 

 condenfation proportionate to this difference will take place. 



Here it is to be obferved, that I have made the rule abfo- 

 lute, or generalized the propofition to every fuppofable cafe ; 

 while, at the fame time, I appealed to familiar examples in two 

 cafes, that is, of humid atmofphere and of pure fteam, in gi- 

 ving the breath of animals in the one cafe, and the fteam of a 

 boiling kettle in the other. 



The propofition being thus made perfetflly general, and con- 

 cluded from experience to be a law of nature, M. de Luc has 

 endeavoured to refute this phyfical principle, by attempting to 

 explain, in another manner, the natural appearances upon 

 which it has been founded. It fhall now be my bufinefs to 

 (how, that this explanation which M. de Luc has endeavoured 

 to give of the fubjed, is founded upon nothing but inadverten- 

 icy or mifapprehenfion. 



He 



