338 ‘Dana on Nitrous Gas® 
this halo intersecting the second on the east and west sides, 
but at that time the intersections on the north side were 
not visible. These appearances were not of long continu- 
ance, nor constant in their arrangement, but, beautiful and 
sublime beyond deseription. _ Unwilling to trust to memo- 
ry as the only memento of such extraordinary phenomena 
| made a sketch at the time, which, imperfect as it Isy 18 
probably the only one taken, and is now respectfully pre- - 
sented you. > loregret that it did: not fall to the lot of some 
person better nalified than meen to describe it. (See 
plate 3. ages . 
halos :tnlbniabve sunin the centre; perhaps the cause 
has been satisfactorily explained, but of those whose peri- 
phery 1 is in-the sun, as respects their locality |. can myself 
form no idea. From what was'seen at that time, | am how- 
ever fully satisfied there is a/possibility of the atmosphere 
being: so charged, as that the whole concave of Heaven 
wou!d be covered with similar appearances. + Ke 
Arr. XVII.—On the Theory of the action of the Hager 
of Azote, or Nitrous Gas in Eudiometry y James 
“reEMAN Dana, Professor of Chemistry Sd pgs 
in Dartmouth College. 
‘Tue deutoxide of azote or nitrous gas appears to be the 
first substance introduced for the express purpose of ana- 
lysing the atmosphere, It_owes its application, in the pro 
cesses — a oaers to Priestley, its discoverer ; iis use 
ded on the facility of its union with oxygene £453 
heal the two gases come in contact, red os ce are pro- 
duced, which Persil fe absorbed by wate 
It appears to be established, by cealipiedd seaierrer 
that the atmosphere contains 21 volumes of oxygene gas ™ 
100; yet the deutoxide of azote has sometimes indicated 
inuch more, at other times much less, and has seldom - 
forded uniform results. Priestley was led to suppose that 
there was a very polo ected difference, as indicated by 
nitrous gas, between the external air, and the air of his 
study after a number of Sersobh had been sitting there 5 3 
= air in the neighborhood of York was not as good 2® 
wear Liveds. Vet there i is not found to be a percept 
f 
