The Rider-Ericsson Engine Company was the successor of the DeLameter Iron Works and the Rider Engine Company, having bought from both companies their extensive plants and entire stocks of engines and patterns, covering all styles of Rider and Ericsson hot air pumping engines brought out by both of the old companies since 1844, excepting the original Ericsson engine, the patterns of which were burned in the DeLameter fire of 1888.
The company specialized in hot air pumping engines. A hot air engine is an external combustion engine. All hot air engines consist of a hot side and a cold side. Mechanical engergy is derived from a hot air engine as air is repeatedly heated and cooled, expanding and contracting, and imparting pressure upon a reciprocating piston.
In his patent of 1759, Henry Wood was the first to document the powering an engine by the changing volume of air as it changed temperature. George Cayley was the first to build a working model in 1807. The Reverend Robert Stirling is generally credited with the "invention" of the hot air engine in 1816 for his development of a "regenerator" which conserves heat energy as the air moves between the hot and cold sides of the engine. Technically, not all hot air engines utilize regenerators, but the term hot air engine and Stirling engine are sometimes used interchangeably.
What's it worth? Take a look at this Rider Ericsson price guide: sold listings for a value indication.