In 1914, Goddard received two U.S. patents, one for a rocket that
used liquid fuel, the other for a two- or three-stage rocket using solid
fuel. At his own expense, he began to make systematic studies about
propulsion provided by various types of gunpowder. This work resulted in
his classic study in 1916 requesting funds from the Smithsonian
Institution to continue his research. This was published along with his
subsequent research in the Smithsonian Miscellaneous Publication No.
2540 (January 1920) entitled "A Method of Reaching Extreme Altitudes."
In this treatise, he detailed a search for methods of raising
weather-recording instruments higher than sounding balloons.