210 Scientifie Proceedings, Royal Dublin Society. 
and that when this is the case the weather is fine, with bright 
sun. The diminution of the amount of carbonic acid in bright 
weather in the country has been assumed to arise from the in- 
creased activity of the chlorophyl in vegetation. In the city the 
diminution eee arises from the production of an active eifour 
lation in the air.’ 
Lastly, we may give the figures obtained by Petermann ad 
Graftiau, which do not support the view that sunlight causes a 
diminution :— i 
| 
General mean of 525 determinations, A } 2:94 
“ Temps beaux,” mean of 217 determinations, . 2°95 
“‘' Temps couvert,’’ mean of 103 determinations, 2:92 8) 
Influence of Height. ~ | 
The influence of height per se, and apart from changes of | 
pressure produced by other causes, has been discussed by several | 
observers. | 
The elder De Saussure was, no doubt, the first of these:—“I | 
was anxious,” he says (in 1787), “‘to know if the gas, whose 
weight is nearly double that of ordinary air, can raise itself to the | 
height of Mont Blanc” ; and he satisfied himself that it could do 
so, both by the lime-water test and by the loss in alkalinity of 
caustic potash when exposed to the air at the summit. His son 
Théodore, in his memorable researches on the amount of atmo- 
spheric carbonic anhydride, and on the causes of its variation, 
came to the conclusion that the amount was actually greater on 
mountains than in valleys. 
The brothers Schlagintweit, in 1849, were, however, the first to 
investigate the question of any possible effects produced by consi- 
derable heights. Their experiments were conducted on the Hastern 
Alps, and the conclusions at which they arrived were—(1) That 
the amount increased from 3°2 to 5:8 vols. in 10,000 up to a height 
of 3365°8 metres, when a constant maximum was reached ; (2) at 
great heights the variations were less than in lower places; (3) the 
atmosphere over a glacier is poorer in carbonic anhydride than in 
its neighbourhood. 
