During the month of April, 1886, we made eighteen estimations of carbonic acid in the air, employing Van Nuys' apparatus,[1] recently described in this journal. These estimations were made in the University Park, one-half mile from the town of Bloomington. The park is hilly, thinly shaded, and higher than the surrounding country. The formation is sub-carboniferous and altitude 228 meters. There are no lowlands or swamps near. The estimations were made at 10 A.M. [Footnote 1: See SCI. AM. SUPPLEMENT No. 577.] The air was obtained one-half meter from the ground and about 100 meters from any of the university buildings. The number of volumes of carbonic acid is calculated at zero C. and normal pressure 760 mm. --------+----------+--------------+------------------------ | | Vols. CO_{2} | Date. | Bar. | in 100,000 | State of Weather. | Pressure | Vols. Air. | --------+----------+--------------+------------------------ April 2 | 743.5 | 28.86 | Cloudy, snow on ground. " 5 | 743.5 | 28.97 | " " " " " 6 | 735 | 28.61 | Snowing. " 7 | 744.5 | 28.63 | Clear, snow on ground. " 8 | 748 | 27.59 | " thawing. " 9 | 747.5 | 28.10 | " " " 12 | 744 | 28.04 | Cloudy. " 13 | 744 | 28.10 | Clear. " 14 | 743.5 | 28.98 | " " 15 | 750.5 | 28.17 | Raining. " 19 | 748 | 28.09 | Clear. " 20 | 746 | 27.72 | " " 21 | 746 | 28.16 | " " 22 | 741.5 | 27.92 | " " 23 | 740 | 28.12 | " " 24 | 738.5 | 28.15 | " " 25 | 738.5 | 27.46 | " " 28 | 738 | 27.34 | " --------+----------+--------------+------------------------