Levis & Bhaxke—The Carbonic Anhydride of the Atmosphere. 188 
On the other hand, the cause for this variation no longer exists 
over the ocean, and according to Levy’s observations, not only does 
the variation itself cease, but it is actually reversed. Thorpe also 
found a minute excess in Atlantic air during the day time. This 
may be explained, as Levy supposed, by the evolution of the 
dissolved gases from the surface layers of the sea as they become 
heated by the sun, and a corresponding absorption as the tempera- 
ture falls at night. From Thorpe’s observations of the air over 
the Irish channel it wouid appear that there was practically no 
variation owing to night and day, which is very interesting, as the 
light ship on which his determinations, were made was only seven 
miles distant from land (the Isle of Man), hence the air which he 
examined was subject to both land and sea influences. 
Hyades also, at Cape Horn, found a slight excess in day air. 
This may be explained by the almost complete absence of vegeta- 
tion there, and also by the fact that the Cape is virtually 
surrounded by the ocean, the temperature of which is higher 
during the day than at night. 
v. Fodor, Wollny,' and others explain the increase in the car- 
bonie anhydride of night air over land surfaces as being due, not 
to the cessation of vegetable activity, but to ground air, which is 
very rich in carbonic anhydride. As night approaches, and the 
temperature falls, the ground air, which is then warmer than the 
atmosphere, escapes in considerable quantities, and, mingling with 
the latter, increases the amount of its carbonic anhydride.? 
Considering the difficulty which has been experienced in tracing 
any considerable variation in the amount of atmospheric carbonic 
anhydride caused by vegetation, and also bearing in mind 
v. Fodor’s observations on air at different heights above the 
surface of the ground, showing what an important influence 
ground air exercises on the amount of atmospheric carbonic anhy- 
dride, we are inclined to believe that v. Fodor’s explanation is in 
the main the true one, more especially as the vegetation theory, 
while possibly explaining diminution during the day time, fails 
to account for the increase at night. 
ly. Fodor, ‘‘ Luft, Boden, und Wasser,”’ p. 538, and Wollny, ‘‘ Forschungen a. d.. 
Geb. d. Agrikultur-Physik,’’ 8 [1885], p. 417. 
* See Appendix on Ground Air, p. 214. 
