92 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



in 1S68, 27 inches; in 18G9, 32.G inches; in 1870,62.5 inches. 

 The evaporation from a basin of water, stationed seven feet 

 above ground, amounted, in 1867, to 82.5 inches ; in 1868, to 

 75.6 inches; in 1869, to 75.9 inches; and in 1870, to 60 inches. 

 But the evaporation from a similar basin placed on the 

 ground is about one half of these amounts. The highest 

 average barometric pressures occur in April, May, June, and 

 July, and the lowest average pressures occur in December 

 and January. The highest temperature of the air recorded 

 by the thermometer shaded from the direct rays of the sun oc- 

 cur in December and January, and reached, in 1867, 113 ; in 

 1868,113.6; in 1869, 108; and in 1870, 112.5. The low- 

 est temperatures recorded by the minimum thermometers 

 shaded from the influence of radiation at night occur in July 

 and August, and were, in 1867, 29.7; in 1868, 24.8; in 1869, 

 29.5; and in 1870, 29.6. Meteorolog. Observations by John 

 Tebbuttj Sydn ey, 1874. 



CARBONIC-ACID GAS IN THE AIR. 



According to experiments that have been made by many 

 chemists since the discovery of carbonic-acid gas, a larger per 

 cent, of this substance is found in the atmosphere in the sum- 

 mer than in the winter, in the proportion of 71 to 48. Bous- 

 singault found that, out of ten thousand volumes of air, B-j%- 

 were carbonic-acid gas during the day, and 4 T 2 ir during the 

 night. Peligot having calculated the quantity of carbonic- 

 acid gas that must result from the burning of oil and coal, 

 from various industrial operations as well as natural phe- 

 nomena, shows that there must be a large compensation, such 

 that the gas produced by one class of operations is decom- 

 posed by another; so that it happens that the proportion 

 of the gas in the atmosphere remains nearly constant, at 

 least at the surface of the ground. The recent balloon as- 

 censions in France have undertaken to determine the rate at 

 which the quantity of gas varies with our ascent in the air. 

 According to the experiments that had previously been made 

 upon mountains, the proportion of gas diminishes slightly with 

 the ascent in the air ; but balloon ascensions have the special 

 advantage that the observer is, by the balloon, carried far 

 above the influence of the soil. The results of the first of 

 the recent voyages in the "Zenith" gave, for carbonic-acid 



