People first began using weather charts in a modern way in the mid-19th century. They began using them to make a theory about storm systems. When a telegraph network developed by 1845, it was possible for people to collect information about the weather. They could get the information from many different places far away quickly enough for the information to be useful. In the 1840s, Joseph Henry took charge. He helped the Smithsonian Institution focus most of its observers on the center and the eastern part of the United States during the 1840s and 1860s. The U.S. Army Signal Corps kept up this network between 1870 and 1874 by an act of Congress. It later expanded to the Western United States.