176 Scientific Proceedings, Royal Dublin Society. 
it and the amount in fresh air is less than 1 in 10,000 (though 
Russell has shown that this is the difference between London air 
and fresh air). 
If we take Miintz and Aubin’s figures for the Plain of Vin- 
cennes and Paris respectively, the mean difference is 0°35, or about 
+ of the amount taken in the above calculation, which would give 
a dilution of the carbonic anhydride thrown into Paris air of 3000 
times. . 
These figures will give some idea, at all events, of the extent 
of the diluting effects occurring in a town by natural agencies. 
In the following table we have collected some typical examples 
of the differences between the air of towns and country. 
Tuer Amount or ATMosPHERIC Carpontic ANHYDRIDE IN Town 
AND CouNTRY. 
CO, in CO, in 
Observer. Town. en Country. tee 
(mean). (mean). 
A. Smith, . , . | Manchester streets, | 4°03 | Manchester (suburbs) | 3°69 
SA AEE 5 . | London, ‘ - |) Beso) | 2mls. from Clapham, | 3°46 
69 inp. wo : . | Perth, : . | 4°14 | Scotland (country), . | 3°36 
Se: x . | Glasgow, . 5s |) OD 4 ss : a 
Mintz & Aubin, =) | Paris; : . | 8:19 | Plain of Vincennes, | 2°84 
Spring & Roland, . | Liége (Belgium), . | 3°35 = == 
Petermann & Graftiau, — — | Gembloux (Belgium), | 2°94 
Carleton Williams, . | Sheffield (town), 3°85 | Sheffield (suburbs), 3°26 
As examples of the effects of purely local conditions the fol- 
lowing may be mentioned. 
The average amount of atmospheric carbonic anhydride found 
by Russell during an investigation of London air extending over 
two and a-half years (January, 1882, to May, 1884), was, excluding 
fogs, 4 in 10,000 volumes, compared with 3 in pure country air. 
“The smallest amount of carbonic acid found in the city air was 
3°0, and this was on a Bank Holiday, August 7th, 1882. In fact 
it appears that the amount is usually low on these holidays, for on 
