The average number of volumes of carbonic acid in 100,000 volumes of air is 28.16, the maximum number is 28.98, and the minimum 27.34. These results agree with estimations made within the last ten or fifteen years. Reiset[2] made a great number of estimations from September 9, 1872, to August 20, 1873, the average of which is 29.42. Six years later[3] he made many estimations from June to November, the average of which is 29.78. The average of Schultze's[4] estimations is 29 2. The results of estimations of carbonic acid in the air, made under the supervision of Munz and Aubin[5] in October, November, and December, 1882, at the stations where observations were made of the transit of Venus by astronomers sent out by the French government, yield the average, for all stations north of the equator to latitude 29 deg. 54' in Florida, 28.2 volumes carbonic acid in 100,000 volumes air, and for all stations south of the equator 27.1 volumes. The average of Claesson's[6] estimations is 27.9 volumes, his maximum number is 32.7, and his minimum is 23.7. It is apparent, from the results of estimations of carbonic acid of the air of various parts of the globe, by the employment of apparatus with which errors are avoided, that the quantity of carbonic acid is subject to slight variation, and not, as stated in nearly all text books of science, from 4 to 6 volumes in 10,000 volumes of air; and it is further apparent that the law of Schloesing[7] holds good. By this law the carbonic acid of an atmosphere in contact with water containing calcium or magnesium carbonate in solution is dissolved according to the tension of the carbonic acid; that is, by an increased quantity its tension increases, and more would pass in solution in the form of bicarbonates. On the other hand, by diminishing the quantity of carbonic acid in the atmosphere, some of the bicarbonates would decompose and carbonic acid pass into the atmosphere. [Footnote 2: Comptes Rendus, 88, 1007.] [Footnote 3: Comptes Rendus, 90, 1144.] [Footnote 4: Chem. Centralblatt, 1872 and 1875.] [Footnote 5: Comptes Rendus, 96, 1793.] [Footnote 6: Berichte der deutsch chem. Gesellschaft, 9, 174.] [Footnote 7: Comptes Rendus, 74, 1552, and 75, 70.] Schloesing's law has been verified by R. Engel[8]. [Footnote 8: Comptes Rendus, 101, 949.] The results of estimations of bases and carbonic acid in the water of the English Channel lead Schloesing[9] to conclude that the carbonic acid combined with normal carbonates, forming bicarbonates, dissolved in the water of the globe is ten times greater in quantity than that of the atmosphere, and on account of this available carbonic acid, if the atmosphere should be deprived of some of its carbonic acid, the loss would soon be supplied. [Footnote 9: Comptes Rendus, 90, 1410.]