United States Weather Maps for 1872-1874. 3 
Diurnal inequality in the progress of storms. 
In order to ascertain whether the progress of storms is uni- 
form throughout the entire day, I availed myself of the 
monthly maps issued by the Signal Service Bureau. These 
maps show the position of the storm centers for three hours 
of the day, viz: at 7.85 A. M., which is designated by (1); at 
4.35 Pp. M., which is designated by (2); and at 11 P. M., which 
is designated by (3). On each storm track, the distance from 
1 to 2, from 2 to 8, and from 8 to 1 (of the next day), was 
4.35 P. M. to 11 P. M.; and the numbers in column fourth 
represent the velocity from 11 P. M. to 7.85 a. M. of the 
following day. 
ae Se | 1-2 | 2-3 3-1 
Jan. | 26-6! 37:3) 28-2/'July | 25-2| 326) 28-2 
Feb. | 28°6: 37-0 28°9|'Aug. | 24°2| 28°6) 20°8 
March | 27-2! 33°6| 27-2) Sept. | 23°9| 30°2| 24°5 
April | 22°56) 25-9) 22-9) Oct. 22°9| 29-6) 23°5 
May | 19-2) 25-6 19-5) Nov. | 33-6) 40°6| 29°3 
June | 22°5| 25-9| 22-2), Dec. | 33°3) 37-0) 29°9 
‘Year, | 25-9 31-9| 25-4 
From this table it appears that the average velocity of 
storms from 4.85 P. M. to 11 P. M. is about 25 per cent greater 
than it is for the remainder of the day. This excess varies 
for the different months, ranging from 14 to 32 per cent, but 
'n each month the most rapid progress occurs during the same 
portion of the day. . 
ee diurnal inequality is doubtless connected with a diurnal 
'nequality in some one and perhaps several of the other 
meteorological elements. Its maximum value apparently oc- 
curs about 7 Pp. M. Now this is not the hour of the maximum 
force of the wind, nor of the maximum or minimum tempera- 
ture, and hence it may be presumed that the inequality does 
not depend directly upon the velocity of the wind nor upon 
the absolute temperature. This hour (7 P. ‘M.) is, however, the - 
time when the temperature of the day is declining most rapidly, _ 
