Studies of the atmosphere first received 13 ______ support in 1912. Equipment to 14 ______ temperature and pressure was invented in Germany. But the question was how to 15 ______ it high into the air. In 1921, Russian engineers suggested using planes. The special equipment was put on planes that made 16 ______ flights. Thanks to this, scientists got a lot of new information about the structure of the atmosphere. Nowadays scientists use modern flying laboratories to 17 ______ the structure of clouds at different levels. Unlike the first planes, these laboratories can work in any weather and are able to 18 ______ climate changes.