36 BULLETIN 102, UNITED STATES NATIONAL MUSEUM. 
property value for equipment that is actually used only a very 
short period out of each year. Every natural gas company must 
have considerable equipment that will be used not over four hours 
daily during say 30 of the coldest days of a year of normal tem- 
perature. The smallness of this is evident from the following: 
Total number hours in the year 24 X 365 = 8, 760 = 100 per cent. 
Hours peak load equipment is actually 
used. 4 X 30 = 120 = 1.4 per cent. 
FIG. IS. ANNUAL AVERAGE NATURAL GAS CONSUMPTION PER DOMESTIC CONSUMER. 
Industrial loads ordinarily are very much more uniform than 
domestic loads. This is especially true of the carbon black industry 
in the field, where the load can be made uniform every day of the 
year. The relationship between maximum, minimum, and average 
load conditions is shown on page 37. 
PEAK LOADS INCREASE COST OF SERVICE. 
An increase of volume of business can decrease the cost of produc- 
tion only when the increment of increase is distributed so as to make 
