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XXL On Evaporation. By John Andrew de Luc, Esq. F.R.S . 
Read June 28, 1792. 
In my last papers on hygrometry, I have considered moisture 
in the air as a modification of a particular fluid, produced by 
the evaporation of water, composed of water and fire, mixed 
with the air, but independent of it. However there was a 
more common theory of that phenomenon, in which evapo- 
ration was attributed to a dissolution of water by air : but as 
an inquiry into the cause of evaporation belongs more to 
hygrology than to hygrometer, I made then no remark on 
that subject ; having in view some experiments which were to 
ascertain a particular point fundamental to it. Since that 
time I have made those experiments, which are the object of 
this paper ; but before I relate them, it is necessary to ex- 
plain how they connect hygrometry with hygrology ; which 
will be by stating the principles of those two branches of ex- 
perimental philosophy according to my system. 
From the time I fixed my attention on evaporation, and its 
various consequences, I was led to think, that the kind of dis- 
solution of water, observed in those phenomena, was operated 
by fire, without any interference of air : and among other 
reasons for that opinion, the most decisive for me was, that 
