Great improvement has been made in the methods of fighting fires and in the character of the apparatus employed, so that the danger from loss by fire has greatly diminished. Furthermore, the more general use of brick and stone for building purposes in the larger cities has made the danger from fire much less than in the old days when most houses were built of wood. Many cities have what are called "fire limits," that is, districts in which it is forbidden to erect wooden buildings. =Municipal Public Utilities.=--People crowded together in cities depend largely upon public service companies for their water supply, for electric light and gas, for telephone service, and for the means of transportation. The furnishing of each of these services, from the very nature of the case, tends to become a natural monopoly. Moreover, such companies must use the city streets in serving their patrons. It follows, therefore, that they must be subject to public control, otherwise the public might be charged exorbitant prices and the use of the streets by the citizens unnecessarily interfered with. Before engaging in a service of this kind, therefore, the street railway company must secure permission from the city to lay tracks on the streets and to operate cars thereon. Likewise a telephone or electric light company must have permission to erect its poles on the streets or alleys, and a gas or water company must have authority to tear up pavements and put its pipes and mains under the streets. [Illustration: MUNICIPAL LIGHTING, DENVER, COLORADO] [Illustration: PART OF THE LOS ANGELES AQUEDUCT, CALIFORNIA This Aqueduct is 11 feet in diameter and carries water from Owens River 246 miles to Los Angeles.] _Franchises._--The permit thus granted is called a "franchise," and is in the nature of a contract between the city and the company. Public service franchises are often of great value to the companies which receive them, for the business of these companies in a large city is apt to be very profitable. Sometimes the dividends which they pay their stockholders are very large, and not infrequently, to deceive the public as to the real amount, the profits are concealed by "watering" the stock, that is, by increasing it beyond the amount of the capital actually invested. Experience has shown that in granting franchises certain restrictions or conditions should be placed on the companies to whom they are granted.