Springfield, Mass. Printed at National Armory 1873. First Edition. 20 pages. Purple printed wrappers, Previously bound, now loose, disbound with the rear wrapper and spine perished. Purple color faded. Clean internally. Last page now soiled, with penciled notations in the lower margin (likely a bookseller stock number). Good. Wraps. 
Although not stated, the second edition of this pamphlet (the first was issued in 1871, and contained only 11 pages). Both are rare (OCLC noting only one location for the 1871 edition, and two for the one offered here [US Army War Coll and Boston Univ]).
This pamphlet describes modifications of "Benton's Electro-Ballistic Pendulum" removing the electrical activiation and replacing it with the thread velocimeter. The modifications are described, tests performed and reported in detail. "The peculiar advantages found in the use of threads over electricity, are simplicity and cheapness of the apparatus, freedom from acid and water for the batteries, and the certainty and ease with which it can be operated by a single person, and that person the one who fires the gun."