C M) 
River Lluyd, which faHs^ich a rapid Stream into tfe 
Iri/h Sea ; and confequently, is feveraJ Foot above the 
Surface thereof. 
May z6. Between One and Two in the Afternoon, on 
the top of Smwdon, I thrice repeated the Experiment, 
and as often found the height of the Mercury i6 Inches i; 
And being come down ioLlanlerris^ at the Foot of the 
Hilt) about Six that Evening, I as often found it 29 In- 
ches 4. A little above this place, are the principal 
Fountains cf the River, that falls into the Cliannel of 
Anglefey^ at Carnarvon, call'd anciently Segontinm^ whi- 
trher wewent the nest Day ; and about Eight at Even, 
found thQ Mercury, by a triple Experiment, to (land at 
29 Inches 9% very near the Surface of the Sea : When,^ 
at the fame time, at Llanerch, it was not above 29 y\ • 
whence I conclude, that the Difference of the Airs Pref- 
fure on the Sea, and on the top of Snowdon, is rather 
more than 3 Inches, 8 Tenths. I could have wilh'd foTr 
one of Mr. Hunt's portable Barometers ; which will cer* 
tainly be accurate enough for taking the Levels, for 
brrnging of Water from diflant places, and certainly 
much lefs fubjed to Error ; there being a Tenth oPan 
lach for each Thirty Yard^, v^hich may be divided into 
many pam evidently, Sncwdcn was meafiired by Mr. Cap 
voel^ with Adams sltAmmtnts^ to be 1x40 Yards high j 
which abacing the height of the Mercury 3 Inches, 
8 Tenths, may ferve for a Standard, 'fill a better be 
obtatded on a higher place. From hence the Sea dipt 
every-where above a Degree below us, the Vifible 
Horizon being a lefler Circle , and we faw Ireland 
plainly, fron W h S \.o SW hw, and then appear- 
ing in the NN W, and the Mountains of Cumherland or 
Wejimoreland very faintly, but evidently in the North; 
and I think we faw as far as Sc. David's Head into the 
iSctorhi CArnarvonjhire and Anglefey lay under us, like 
