Observations of the United States Signal Service. 3 
pressure expressed in English miles; column 11th shows the 
direction and force of the wind at the place mentioned in col- 
umn 4th and at the date given in column 2d; and column 10th 
shows the direction and force of the wind at the observatio 
next preceding the date mentioned in the table. : 
For each of the cases named in this table, the curves of equal 
rain-fall have been accurately drawn upon maps of the United 
States, and these curves have been carefully compared. The 
following table shows the geographical extent of some of 
these rain-areas. Column Ist shows the number of reference 
taken from the preceding table; column 2d shows in English 
miles the greatest and least diameters of the area over which the 
rain-fall was at least one inch in eight hours; and column 8rd 
shows the greatest and least diameters of the area over which 
the rain-fall was at least half an inch, in eight hours. 
Dimensions of Rain-areas. 
Area of Area of Area of Area of Area of Area of 
No.{ one inch half inch No, | one inch halfinch || No. |} one inch balf inch 
rain. rain, rain. rain. rain. rain. 
10 | 720-230 | 920-398 443-167 | 714-393 || 20} 338-173 | 890-406 
17 
9 | 605-334 | 668-430 || 36 | 440-160 | 858-356 |} 54 | 338-194 | 458-358 
45 | 546-318 | 724-350 || 27 | 380-296 | 468-390 7 | 320-288 | 394-312 
39 | 490-188 | 514-236 || 32 | 374-150 | 796-340 5 | 312-276 | 394-394 
6 | 360-304 | 440-402 1| 300-174 | 494-300 
55 | 468-162 | 652-312 
446-216 2 
1 
174-33 8 | 354-144 | 436-266 || 18 | 242-162 | 858-224 
The form of these rain-areas is sometimes quite irregular but 
generally it approximates to an ellipse of which the major axis 
is not quite double the minor axis. This elongated form of 
rain-areas is more noticeable in storms whieh prevail near the 
Atlantic coast, than it is in regions remote from the ocean. It 
will be seen that in three cases the area of one inch rain-fall 
exceeded 500 miles in length, and in six cases the area of one 
half inch rain-fall exceeded 750 miles in length. In number 
_ ten, the area of one quarter inch rain-fall was 1,180 miles by 500 
miles ; in number twenty, this area was 1,000 miles by 572 miles, 
and in two or three other cases the dimensions of the rain-areas 
were nearly as great. Frequently the’entire rain-area is an oval 
figure whose length exceeds 1,000 miles, and whose breadth 
exceeds 500 miles. ig 
It was shown in my sixth paper, that south of latitude 36° 
rain-areas are as frequently under the influence of an area of 
high barometer as of an area of low barometer. In columns 7, 
8 and 9, of the table on page 2, I have therefore left blanks for 
the southern stations) The numbers in*column 8th, for the 
northern stations, show that in seventeen cases the rain center 
was north of the center of low pressure, and in sixteen cases it 
was south of this center. In twenty cases the rain center was. 
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