This is a flow regulator for liquid oxygen, also called a lox [flow] indicator, and was used by Robert H. Goddard for some of his earliest liquid fuel rocket experiments, about 1923-1924.
Mrs. Robert H. Goddard donated this object to the Smithsonian Institution in 1959 as part of a large collection of artifacts from her husband.
This object is not on display at the National Air and Space Museum. It is either on loan or in storage.