42 



MEMOIES OF THE NATIONAL ACADEMY OF SCIENCES. 



No. 6 was a storm similar to No. 1, witli equally violent winds, and a somewhat greater fall of 

 rain, and tbe greatest rainfall was on the north and northwest sides of the low center. Table 

 XXV shows the rainfall at ten stations during a period of two days. 



Table 'KXY .—Rainfall Septemher 16.2 to 18.1, 1876. 



Charlestoii. . . 

 Wilmington . 



Norfolk 



Washington . 

 Cape May . . . 

 Baltimore . . . 

 Philadelphia 

 New York . . . 

 Pittsburgh . 

 Erie 



16.2 



0.03 

 .57 

 .70 

 .01 

 .01 

 .03 

 .00 



■.00 

 .00 

 .00 



No. 11 was an area of low pressure which traveled eastward near the parallel of 50°, and when 

 it had passed a little beyond Quebec was for a few hours diverted towards the southwest. This 

 westward movement of the low center was accompanied by a considerable fall of snow in the 

 neighborhood of Lakes Erie and Ontario. Table XXVI shows the amount of the precipitation 

 (reduced to water) at live stations during a period of twenty-four hours. 



Table XXVI. — Fall of snow {reduced to water) March 23.3 to 24.2, 1878. 



No. 12. The northerly and westerly movement of this low area on the afternoon of April 

 28 was accompanied by a considerable rainfall on its northwest side, and there was also on the 

 northwest side a second low area, which was traveling eastward, and which coalesced with the 

 former on the evening of April 29. The latter cause may have promoted the westerly movement 

 of No. 12. 



No. 13 was similar to the preceding. The movement of this low center towards the north- 

 west on the afternoon of June 22 was accompanied by considerable rain on the northwest side of 

 the low center, and there was also on the northwest side a second low area which coalesced with 

 the former on the following day. 



No. 14. There was a heavy fall of snow in the neighborhood of the Gulf of Saint Lawrence, 

 in connection with this storm, and there are indications that this snow-fall had some influence upon 

 the movements of this low area, but, as I have no observations except those published in the 

 International Bulletin, and as these are given but once a day, the evidence is not entirely 

 satisfactory. 



No. 24. The diversion of this low center towards the southwest on the afternoon of March 

 25 was aijparently the i-esult of a heavy fall of rain in Texas. 



III. When two centers of high pressure are situated within a few hundred miles of each 

 other a feeble system of circulating winds frequently springs up between them, and if there is a 

 considerable fall of rain or snow a new center of low pressure is usually formed, and this may 

 occasion abnormal movements in a neighboring area of low pressure, in the manner described in 

 Paragraph I. 



No. 20 affords an illustration of this principle. There was a center of low pressure over North 

 Carolina, with a center of high pressure over Newfoundland, and another over Montana. Between 



