United States Weather Maps. 13 
measured, and the distance recorded under the corresponding 
velocity found at the top of one of the vertical columns. 
the weather maps for 1872 and 3’ were examined in this manner, 
and the distance between the isobars recorded. The following 
table shows the average results : 
Relation between the velocity of the wind and the distance between the isobars. 
Veloc. | No. of | Mean Ay. | Dist.in || Veloc. | No. of | Mean | Av. | Dist.in 
miles. | Obs. distance|distance| miles. || miles, Obs, distance distance) miles. 
0 69 “79 Subs mee 20 76 *63 61 95 
1 55 90 ae wad ZI 9 56 62 97 
2 81 "90 ‘86 134 22 23 65 62 97 
Z 87 "86 34 23 13 65 62 97 
4 176 83 "84 131 24 40 59 62 97 
5 111 82 82 128 25 13 65 “61 95 
6 168 80 "80 125 26 5 56 *b9 93 
7 76 “19 123 pays 5 9 *b8 0 
8 230 78 “78 122 28 20 56 54 85 
9 17 “16 119 29 4 54 *b4 85 
10 129 V7 “45 117 30 15 46 52 81 
11 6 Th “14 115 St 4 54 50 78 
12 262 72 ay ts 114 32 7 51 ‘48 75 
13 74 “69 109 33 0 io “46 2 
14 93 70 “68 106 34 a “44 69 
15 60 67 104 35 4 39 ox “e 
16 122 64 “64 100 36 4 *39 pug ies 
17 26 | -65 | :62 37 0 af 3 we 
18 66 “60 62 97 38 0 ig wes ae 
19 10 60 61 95 39 0 nN Be oa 
Column first shows the velocity of the wind in miles per 
hour ; column second shows the number of observations corre- 
sponding to each velocity; and column third shows for each 
velocity the average distance between the isobars expressed in 
decimals of an inch. It will be noticed that the numbers in 
column second are very unequal ; the number of observations 
for velocities 4, 8, 12,16, 20, 24 and 28 being much greater 
than for the intermediate velocities. This shows that the 
velocities are not reliable within 1 or 2 miles, and this proba- 
bly explains in part the irregularity of the numbers in column 
third. In order to smooth down these irregularities, I have 
column fourth may, therefore, be regarded as exhibiting the re- 
sults of the observations freed from some of the sources of error 
rawn at intervals of one-tenth of an inch) sede ae to 
the velocities given in column first. The average di 
the stations of observation from the center of low barometer is 
