Observations of the United States Signal Service. 17 



anywhere near the path of the storm, was thirty-eight miles per 

 hour (on Mt. Washington), indicating that the progress of the 

 low center was not due wholly to the transfer of air Irom west to 

 east, but rather to a dimimit<on of the pressure on the east side 

 of the low. and an increase of the pressure on its western side. 



In No. 11 Lynchburg was somewhat nearer to a center of 

 hidi pressure than of low pressure. There are indications that 

 a small local cyclone formed about Lvnchhiirg. but the stations 

 of ohservation'arc too tew to show this conclusively. 



In Nos. 20 and 21 the rain center was much nearer to a center 

 of high pressure than of low pressure. At 4.35 P. U. a distinct 

 local evclone was shown about Baltimore, Washington, and 

 Capo May. but the cyclonic area was of small diameter and its 

 effect upon the barometer was scarcely appreciable. 



We thus see that great rain-falls may occur under the influ- 

 ence of an area of high pressure as well as of low pressure, and 

 when they occur at a great distance from a low center, they are 

 generally accompanied by a distinct local cyclonic movement 

 of the atmosphere. 



Of the thirtv-one cases ineluded in the preceding table, fifteen 

 occurred on the Atlantic coast, and the number of stations of 

 observation upon the coast was eleven ; which shows an average 

 of l - 37 to each station. For the remainder of the United States 

 there were sixteen cases, and the number of stations was tiftv- 

 nine, showing an average of 027 to each station. Thus we see 

 that north of lat, 36° near the Atlantic coast, great rain-falls are 

 fire (.me* as frequent as in other parts of the United States in 

 the same latitude. The frequency of heavy rain-falls in the 

 neighborhood of the great lakes is" not sensibly greater than at 

 inland stations quire distant from the lakes. 



The distribution of these 31 cases by seasons was as follows : 

 Spring 3 ; summer 15 ; autumn 6 and 5 ; winter 2. 

 Showing a predominance of great rain-falls in summer even 

 mure decided than at the southern stations. 



The distribution of these cases according to the hours of the 

 day was as follows: 7 -35 A.M., 1-4 cases; 435 P. M., 9 cases; 11 

 p. k, 8 cases. 



If we correct these numbers for the inequality of the time 

 intervals, there is still an excess of eases for the morning hour 

 of observation. 



The foil- ; 1 the cases in which aoj 



heavv rail - ' < '' by at least one inch of rain 



! eriod of eight hours. 



At. the Boutha) a ' " cases of heavy rain 



there were twelve cases in which heavy rain continued through 

 two periods of eight hours; at the northern stations out of 



