30 E. Loomis — Contributions to Meteorology. 



the date of each observation being shown by the figures 2*1 ; 

 2-2 ; 2-3 ; 3'1, etc. During the progress of this storm, the pres- 

 sure at the center of the low area underwent great changes. 

 The following table shows for each of the dates, the lowest 

 pressure reported at any of the stations. 



Date. 



Station. 



Baron, 



Date. 



MO* 





Date. 



Station. 



Ha,,, 



Dec. 2.1 



Denver, 



Dubuque. 



l 



|Dec.3.2 



Chicago, 

 Escanaba, 



- J -il 



Doc. 4.: 

 5.1 



MS 



2'J-2* 



We see that the pressure at the center of the low area de- 

 creased until Dec. 4, at 7£ a. m., and this was more than eight 

 hours after the time when the rain-fall had reached its maxi- 

 mum ; also the pressure slowly increased as the amount of 

 rain-fall decreased. These facts appear to illustrate the inertia 

 of the atmosphere ; the minimum of pressure having occurred 

 considerably later than the maximum of rain-fall, and the pres- 

 i slowly restored even when the rain-fall had apparently 



this case accord substantially with 

 those found in a large number of other cases. In all of the 

 cases shown in the table on page 17, the rain-fall west of the 

 meridian of 100° was well-nigh inappreciable, and the rain-fall 

 increased rapidly as the low area moved eastward. Whenever 

 there was a heavy rain-fall west of the meridian of 85°, the 

 rain almost invariably declined before reaching the Atlantic 

 coast. The heavy rain-falls near the Atlantic coast generally 

 commence in the south and follow the Atlantic coast towards 

 the northeast. 



The facts here developed confirm the remark made in my 

 7th paper that "the forces which impart that movement to the 

 air which is requisite to an abundant precipitation of its vapor, 

 instead of deriving increased force from a great fall of rain, 

 rapidly expand themselves and become exhausted." In the 

 case of No. 1, the decrease in the rain-fall was apparently 

 caused by a very cold westerly wind which followed the low 

 area and attained in many places a velocity of 40 miles per 

 hour, and in one place a velocity of 49 miles per hour. The 

 following table shows the fall of temperature in 24 hours at 

 various stations during the progress of this storm, and it will 

 be noticed that these changes were independent of the ordinary 

 diurnal variation of temperature. 



