I just added the below two captions to the Alto Trombone Timeline. This addition brings to 21 the total number of 19th century trade catalogs that clearly label the alto trombone an E-flat instrument (see here). What is the historical significance? This is yet another piece of evidence that runs counter to what some historians have asserted about the alto trombone: 1) That alto trombone was not used (or was rarely used) in the mid-to-late 19th century, and 2) that the alto trombone was just a tenor trombone in B-flat with a smaller mouthpiece. This new evidence is not conclusive by itself; rather, it is part of a large body of evidence (e.g., see the rest of the Alto Timeline, which includes more than 100 primary sources, plus Alto Trombone in 19th Century Trade Catalogs, Alto in Treatises, and Extant Altos). See also this noteworthy recently-published letter by Johannes Brahms from the year 1859, wherein Brahms advocates very strongly for a “genuine little alto trombone.”
c. 1860—New York: John F. Stratton offers two different models of “E-flat Alto Trombone” in his musical instrument catalog, one under the heading of “J. Latour Paris, France,” and another under the heading of “Stratton’s ‘Concerto’ Band Instruments” (University of California, Santa Barbara Romaine Collection).
c. 1860—New York: In a catalog labeled “Appendix to our Musical Merchandise Catalogue,” John F. Stratton offers an “E-flat Alto Trombone” under the category of “Stratton ‘Concerto’ Trombones.” Pictured is an engraving of a valve alto trombone that is shorter than the B-flat tenor pictured (University of California, Santa Barbara Romaine Collection).