[ 4*5 ] 
with Vapours of a certain uniform Denftty, and in- 
tirely proper for feparating an homogeneous Light 
thofe Rays of the heterogeneous Light, which are 
the lead refrangible, or which produce the red Co- 
lour, were accordingly feparated by Reflexion and 
Refra&ion in great Quantities, and coloured the 
whole Sky with a firy Rednefs. And where the 
Light was brighteft, viz. between the North and 
Weft, which is generally the Focus of Aurora Bo - 
reales? there likewife the Rednefs was ftrongeft. 
HI. An Attempt to examine the Barrows in 
Cornwall, by Stephen Williams, M. D . 
F. R. S. 
I T may not be improper to obferve, that thefe 
Barrows? or conical Hillocks, are generally fituated 
on Places of Eminence, on or near the Summit of 
Downs, and fo capable of being feen at a great 
Diftance ? and likewife very often near the moft 
public or greateft Roads, though fometimes in in- 
clofed or fenced Lands, but not often : They lie 
fometimes Two, Three, even Seven, in a ftraitLine, 
now-and-then only One or Two by themfelves : 
Sometimes alfo the fingle ones feem to regard, in 
refpe£t of their Pofition, a greater Number, as is 
obfervable in Tab. I. N° iv. where the Urn was found, 
and N° v. on the fame Down. 
The Height and Dimenfions of the Barrows in 
Cornwall , are various, from Four to Thirty Feet high, 
and from Fifteen to One hundred and Thirty broad ; 
O o o but 
