This is the 1915 Deseret hardcover (7th Printing) of KEY TO THE SCIENCE OF THEOLOGY, by Parley P. Pratt; pocket sized (approx. dimensions 6.25" x 4" x .25"); 159 pp.
The cover has scuffs, edge rubbing and fraying, and chip-offs at the spine head and heel areas; former owner's name on the fep; otherwise still a serviceable copy, with solid binding and clean, unmarked text.