Doubtless, the public does not realize that the enormous decrease in the cost of lighting during the past century is due largely to the fact that the lighting industry has grown large. Increased production is responsible for some of this decrease and science for much of it. The latter, having been called to the aid of the manufacturers, who are better able by virtue of their magnitude to spend time and resources upon scientific developments, has responded with many improvements which have increased the efficiency of light-production. Some figures of the Census Bureau may be of interest. These are given for 1914 in order that the abnormal conditions due to the recent war may be avoided. The figures pertaining to the manufacture of gas for sale which do not include private plants are as follows for the year 1914 for this country: Number of establishments 1,284 Capital $1,252,421,584 Value of products (gas, coke, tar, etc.) $220,237,790 Cost of materials $76,779,288 Value added by manufacture $143,458,502 Value of gas $175,065,920 Coal used (tons) 6,116,672 Coke used (tons) 964,851 Oil used (gallons) 715,418,623 Length of gas mains (miles) 58,727 Manufactured products sold Total gas (cubic feet) 203,639,260,000 Straight coal gas (cubic feet) 10,509,946,000 Carbureted water gas (cubic feet) 90,017,725,000 Mixed coal- and water-gas (cubic feet) 86,281,339,000 Oil gas (cubic feet) 16,512,274,000 Acetylene (cubic feet) 136,564,000 Other gas, chiefly gasolene (cubic feet) 181,412,000 Coke (bushels) 114,091,753 Tar (gallons) 125,938,607 Ammonia liquors (gallons) 50,737,762 Ammonia, sulphate (pounds) 6,216,618 Of course, only a small fraction of the total gas manufactured is used for lighting. According to the U. S. Geological Survey, the quantities of gas sold in this country in the year 1917 were as follows: Coal-gas 42,927,728,000 cubic feet Water-gas 153,457,318,000 " " Oil-gas 14,739,508,000 " " Byproduct gas 131,026,575,000 " " Natural gas 795,110,376,000 " "