248 E. Loomis — Contributions to Meteorology. 



supplanting the southerly winds which had preceded. The 

 barometric gradients within the rain areas were small, and the 

 rain-fall in the southwest quadrant had but little influence in 

 determining the general movement of the winds about the low 

 center, because the southerly winds were soon supplanted by 

 the advancing west and northwest winds. 



7. There is generally a marked uniformity in the changes of 

 pressure and temperature accompanying the eastward progress 

 of an area of low pressure. In front of the low area the pres- 

 sure diminishes, and in the rear the pressure increases. For 

 the 106 cases under examination, the average diminution of 

 pressure in eight hours on the front side of the storm was 0*24 

 inch, and the average increase of pressure on the rear side was 

 012 inch. For different storms, however, those numbers were 

 very unequal. In some of the cases the barometer fell more 

 than half an inch in eight hours in front of the storm, and in 

 one case the barometer fell 0"86 in eight hours. On the other 

 hand there were several cases in which the barometer remained 

 nearly stationary during the eight hours preceding the approach 

 of the low center. 



There were four cases in which the rise of the barometer in 

 the rear of the storm exceeded O40 inch in eight hours. There 

 were several cases in which for eight hours the barometer was 

 almost entirely stationary in the rear of the storm ; and there 

 were two cases in which there was an average diminution of 

 pressure amounting to four or five hundredths of an inch dur- 

 ing the eight hours succeeding the passage of the storm's cen- 

 ter. These cases, in which the pressure remained nearly 

 stationary for eight hours preceding or following the low 

 center, generally resulted from the interference of a second 

 area of low pressure. When an area of low pressure is pre- 

 ceded by a second area of low pressure, within a distance of a 

 few hundred miles, the fall of the barometer in front of the 

 first low center is generally very small ; and when an area of 

 low pressure is followed immediately by a second area of low 

 pressure, the rise of the barometer in the rear of the first low 

 center is generally very small. 



8. For the 106 cases under examination, there was an aver- 

 age rise of the thermometer amounting to seven degrees during 

 the twenty-four hours preceding the approach of the low 

 center ; and there was an average fall of eight degrees during 

 the succeeding twenty-four hours. These numbers, however, 

 fluctuated from twenty-eight degrees to zero, over a large 

 geographical area, and in individual cases the fluctuations were 

 considerably greater. In a few cases there was a noticeable 

 correspondence between the magnitude of the barometric and 

 thermometric fluctuations attending the progress of a low 



