466 Mr. Wilson’s Account of a mojl 
ter in both cafes pointed to +22°. About 1 1 o’clock the 
fun-fhine broke through the fog, when the temperature' 
of the hoar-froft was as quickly affedted as that of the 
air. The air on this day was quite ft ill, and equally cold 
both at the upper and under ftations. It may alfo be 
here obferved, that no fnow lay on the ground. The 
ninth experiment was alfo repeated, but the thermome- 
ter was not now in the leaft affedted by fwinging it 
round. Neither on this occafion, nor when the experi- 
ment was firft made, did any of the frozen matter ap- 
pear to have parted from the ball. 
If we confider the excefs of cold in the fnow which 
Dr. Irvine and I firft obferved as a phenomenon of the 
fame kind with that defcribed in the feventh experi- 
ment, and proceeding from the fame caufe, it is mani- 
feft that neither the one nor the other can be accounted 
for by any previous cold ftate of the air, according to an 
hypothelis alluded to in the beginning of this letter: for 
in the feventh experiment the air at the balluftrade was 
never colder than + io 9 , and yet the hoar-froft there was 
at the fame time found in feveral inftances as cold as 
+ 2 0 . That both thefe phenomena are of the fame kind 
appears extremely probable from this conlideration, 
namely, that when the fnowmpon the fields was atten- 
tively examined, the furface was found quite covered 
over 
