B. TERRESTRIAL PHYSICS AND METEOROLOGY. m 



proportion diminishes quite rapidly as we ascend in the at- 

 mosphere, a fact not at all remarkable when we reflect that 

 it is at the surface of the earth that carbonic acid is pro- 

 duced, and that it is sensibly heavier than the air itself. The 

 diffusion of the two gases, however, carries the carbonic acid 

 to a considerable elevation, but this is not suflicient to satu- 

 rate the air at a very great height. 6 J3 y 1873, 585. 



THE LAWS OF STORMS IX NORTH AMERICA. 



An important memoir on the laws of American storms 

 w r as recently presented by Professor Loomis, of Yale College, 

 to the National Academy of Science, and has lately been 

 published in a revised edition. The conclusions arrived at by 

 Professor Loomis w T ere derived from an examination of the 

 United States weather-maps, as issued from the Army Signal- 

 office. Among the results attained by him, he states that 

 the greatest daily velocity with which storm centres move 

 alons: the earth's surface is found in Februarv, the lowest in 

 August. The average direction of the storm paths is more 

 northerly in October than in July. Very rarely do storms 

 travel in a west or northwest direction. Among the disturb- 

 ing causes affectinGf the direction of the movement of a storm 

 centre, he states that there must be a connection between it 

 and the fall of rain (as has been established by numerous 

 other investigators), and finds with reference to American 

 storms, as an exact result, the following general law : that 

 the average velocity of the storm progress is about thirty- 

 nine miles per hour when the extent of rain area is 600 miles 

 in advance of the storm, but its velocity is fourteen miles per 

 hour when the rain area extends 350 miles in advance of the 

 storm. The average course of the storm paths coincides 

 very closely with the axis of the area over which rain falls 

 during the preceding eight hours; the stronger the wind on 

 the west side of a storm, the less is the velocity of the storm 

 progress. At the height of 0000 feet, in the western quad- 

 rant of a storm, the velocity of the wind is more than double 

 the rate of the storm's progress. The isobares inclosing the 

 storm's centre in more than half the cases examined by him 

 were elliptical, the major axes being half as long again as the 

 minor axes. In a small number of storms the major axis was 

 at least four times the minor. The longer axis most fre- 



