Unfortunately it has been found that this system of communication is not satisfactory even under favorable conditions. This system depends upon direct sunlight; without it is useless. When there is much smoke in the air it is also of uncertain value. The heliograph system has perhaps reached its greatest development upon the California National Forest, but even here experience has shown that it is only a temporary makeshift and the plan is to replace it by a telephone system as soon as possible. The Forest Supervisor, especially in his summer headquarters, depends directly upon the mail service for communication with the District Forester and the outside world. In many cases the fact that the Forest Supervisor has his headquarters in a small mountain community in the summer has made it possible for that community to receive a daily mail service or mail at least three times a week. When the Forest Supervisor becomes satisfied that mail service is desirable in certain mountain communities he investigates local settlers' needs for mail facilities; or he may coöperate with the people in the nearest village who are petitioning for mail service. Often his influence proves the deciding factor in getting it. As I have said before, telephone communication is indispensable to fire protection and to quick and efficient methods of conducting National Forest business. Not only do Forest Service lines enter into the National Forest telephone system but all private lines are also made use of. By coöperative agreements with private companies the National Forest lines are used by private companies, in return for which private lines are used by the Forest Service. In this way a complete network of telephone lines is established connecting not only the Forest Supervisor with all his Rangers and his forest fire lookout stations, but also connecting each one of these with local communities and the large towns at a distance. Thus, when a forest fire occurs and the available local help is not sufficient to control the fire the telephone system is put to use to call help from the nearest villages and towns. [Illustration: Figure 16. Forest Rangers repairing a bridge over a mountain stream. Arapaho National Forest, Colorado]