PHILOSOPHICAL SOCIETY OF WASHINGTON. 



Ill 



Observations of air-pressure and temperature at Denver and Pike', 

 Peak, Colorado, in November, 1880. 



From these observations we see that, although the air-pressure 

 was at a minimum at Denver, November 15, 3 p. m., yet, owing 

 to the extraordinary cold, the pressure continued to fall at Pike's 

 Peak, (which is 8,840 feet above Denver,) and did not reach its 

 lowest point until forty hours afterward, or November 17, 7 a. m. 

 Extending the same reasoning to the diurnal range of air-pressure 

 we shall find a satisfactory solution of the retardation. From 

 hourly observations at the summit and base of Mount Washington 

 I find that while the morning maximum occurs at 8 : 30 a. m. at 

 the base, it does not occur till noon at the summit, during this part 

 of the day the temperature is rising rapidly ; and hence we may 

 suppose that it produces the continued rise in air-pressure at the 

 summit overbalancing the diurnal range; in like manner the after- 

 noon minimum occurs at 6 p. m. at the summit, or two hours later 

 than at the base, as the temperature begins falling at 2 p. m. This 

 may account for the difference at the two stations. On comparing 



