36 



Composition of the Atmosphere 



pies collected on the 1st and 15th of each month at about the hour of 

 true midday in each place. The samples were then sent to Paris, where 

 they were analyzed by explosion with hydrogen in the apparatus used 

 for analyzing the samples of Paris air. 



About 100 analyses were made of air collected in Paris or its suburbs, 

 the larger number being taken at the observatory of the College of France. 

 A part of the results are given in table 12, showing the variations on the 

 different days and the accuracy of the analyses made on the same sample 

 as indicated by the close agreement of the duplicate determinations. 



The smallest amount of oxygen found was 20.913 per cent, the largest 

 20.999 per cent, and the general average, 20.96 per cent. The extreme 

 difference, 0.086 per cent, is greater than the errors resulting from the 

 experiments themselves, for this rarely exceeds 0.02 per cent. Regnault 

 concludes that the absolute change is so small that one can easily attrib- 

 ute this to local alterations which would be frequently found in the center 

 of large cities. He notes further that the variations found at different 

 hours of the same day are no smaller than the variations between days. 



The results of the analyses of air collected at other points in France are 

 given in table 13. 



Table 13. Regnault's analyses of air collected in France outside of Paris. 



Table 14. Regnault's analyses of air collected in Berlin. 



Samples were also collected at noon in Berlin by Magnus from Feb- 

 ruary 1, 1848, to July 1, 1849; at the Madrid Observatory in 1848; and at 



