221 
whilst at Manchester , on the same day, the volume of carbonic 
acid was found to he 2‘8 in 10,000 vols. of air. 
The maximum quantity of carbonic acid was found in 
Manchester air on January 7th, 1864, (on which day there 
was a dense fog) when the amount reached 5*6 vols. per 
10,000 of air; the minimum quantity on February 19th, 
1863, being 2.8 vols, per 10,000 of air. The mean of 46 
determinations made in the centre of the town of Manchester, 
gives the volume of carbonic acid as 3'92 in 10,000, and 
that of eight experiments made outside the town gives the 
number 4'02 as the composition of the country air regard- 
ing carbonic acid. These numbers closely agree with a 
determination by weight which I made in London, on 
February 27th, 1857, from which the carbonic acid in 
London air was found to be 3‘7 vols per. 10,000. 
Experiments 47, 48, and 49 prove that continuous rain 
may lower the amount of atmospheric carbonic acid from 
4*8 to 3'3 volumes per 10,000. 
The above results show that the maximum quantity of 
carbonic acid contained in Manchester air, even in a dense 
fog, and when there is no wind, does not exceed 6 volumes 
per 10,000 of air; whilst the mean quantity, 3 9 volumes, 
closely agrees with that (4*0) generally assumed, from Saus- 
sure’s early experiments, to represent the average composition 
of the atmosphere as regards carbonic acid. 
