Observations of the United States Signal Service. 9 
in 1872-3, when the barometer was unusually low at St. Paul, 
it was unusually high in Oregon or Dakota. The following is 
an example: 
Date. St. Paul. 
1872, Nov. 13 29°92 30°52 
; 14 
eter at St. Paul stood at 28°05. 
Form of areas of maximum and minimum pressure. 
In preceding articles (this Jour., vol. viii, p. 11, and vol. x, p. 9) 
T have shown the ave f f the isobars about a storm 
center as derived from observations of three years. I have since 
made a similar comparison of observations of three years (1873-5) 
to determine the form of the isobars about an area of maximum 
oneede The isobar selected has generally been that of 30°20; 
ut when the observations were insufficient to show the complete 
form of this curve, I have taken the isobar 30°30, provided that 
curve was nearly complete. When both of these curves were 
