( 214 ) 
thing in it analogous to what we obferve in Fogs and 
Clouds, which at nDiftance have indeed the Appear- 
ance of very thick Bodies, but are found more rare 
as one gets into them. Nor is it improbable, as they 
inufl: be foinething very thin and fubtle, that upon the 
Approach of groller Bodies with their Atmofpheres, 
they are aftually driven away. 
This is the Subftance of what I have been able to 
gather from feveral Accounts relating to the Ignes 
Fatui ; but as to the Caufes of them, I will not pre- 
tend to alTign any : I will only add, that all that ever 
faw any of thefe fiery Appearances agree, and you 
may alTure Mr. Derham of it, that they caft a Light 
quite different from that of the Jhming Flies , and 
if you pleafe to reded: on the feveral Circumftances 
above related, I believe you will find, that they are 
not eafily, if at all, to be folved by that Hypdthelis. 
" intend in another Letter to trouble you with fome 
d:ions, and likewife fome Obfervations of my 
' thefe Flies, mean while, 
I am, 6cc. 
« 
VI. Du^ 
I 
