The smoking of chimneys is costly, in the first place, because it is due to imperfect combustion and the waste of part of the heating value of the fuel, and, in the second place, on account of the damage wrought by the deposit of the soot. Thus a smoky atmosphere entails big laundry and dry-cleaning bills, frequent repainting of houses, injury to metal work, damage to goods in shops, and excessive artificial lighting in the daytime. Throughout the United States it is said that smoke causes an annual waste and damage amounting to five hundred million dollars. In Pittsburgh alone--before the reform produced by vigorous legislative and scientific measures, following an exhaustive investigation by the Mellon Institute of Industrial Research--the cost of the smoke nuisance was estimated at nearly ten million dollars a year. Means of mitigating this evil include the introduction of improved appliances for burning soft coal, and the use of other kinds of fuel. The electrification of the railway lines entering cities is an important measure of relief. It is estimated that more than one-third of the smoke found in certain American cities comes from locomotives. Systematic measurements of the amount of solid matter contributed to the atmosphere by smoke have been made at various places in this country and abroad, and yield startling figures. Measures of the “sootfall” in Pittsburgh, before the evil there was mitigated, showed an annual average deposit amounting to 1,031 tons per square mile. London’s average is 248 tons per square mile for the whole city and 426 tons in the central districts. In the heart of Glasgow the annual sootfall is 820 tons per square mile. In Great Britain measurements and analyses of soot and the study of its effects have been carried out on a large scale for a number of years by the Advisory Committee on Atmospheric Pollution, attached to the Meteorological Office. The Committee has installed “pollution gauges,” of uniform type, at about twenty-five places in England and Scotland. The soot that falls into these gauges is collected once a month, weighed and analyzed. This organization also makes direct measurements of the purity of the air, and has acquired a unique body of observations that can be used to test the success of efforts made to abate the smoke nuisance, besides providing interesting comparisons between the incidence of respiratory diseases and the amount of solid matter in the air. CHAPTER V WEATHER AND WEATHER INSTRUMENTS