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XX. An Account oj Three Volcanos in the Moon. By William 
Herfchel, LL.D. F.R.S . ; communicated by Sir Jofeph Banks, 
Bart . P. R. S . 
Read April 26, 1787. 
I T will be necefiary to fay a few words by way of intro- 
du£tion to the account 1 have to give of fome appearances 
upon the moon, which I perceived the 19th and 20th of this 
month. The phenomena of nature, efpecially thofe that fall 
under the infpe&ion of the aftronomer, are to be viewed, not 
only with the ufual attention to facts as they occur, but with 
the eye of reafon and experience. In this we are however not 
allowed to depart from plain appearances ; though their origin 
and fignification fhould be indicated by the moft charadterifing 
fexitures. Thus, when we fee, on the furface of the moon, a 
great number of elevations, from half a mile to a mile and an 
half in height, we are ftri&ly intitled to call them moun- 
tains ; but, when we attend to their particular fhape, in which 
many of them referable the craters of our volcanos, and 
thence argue, that they owe their origin to the fame caufe 
which has modelled many of thefe, we may be faid to fee by 
analogy, or with the eye of reafon. ;Now, in this latter cafe, 
though it may be convenient, in fpeaking of phenomena, to 
ufe expreffions that can only be juftified by reafoning upon the 
fa&s themfelves, it will certainly be the fafeft way not to 
negledt a full defcriptiou of them, that it may appear to others 
K k how 
