This book presents the results of photometric measurements of the variable stars B Persei and DM 810 25 made at the Harvard College Observatory in the early 20th century. The authors describe the methods used in their research and provide detailed data on the brightness and variability of the stars studied. The book also includes a wealth of illustrations and charts. This work has been selected by scholars as being culturally important, and is part of the knowledge base of civilization as we know it. This work is in the "public domain in the United States of America, and possibly other nations. Within the United States, you may freely copy and distribute this work, as no entity (individual or corporate) has a copyright on the body of the work. Scholars believe, and we concur, that this work is important enough to be preserved, reproduced, and made generally available to the public. We appreciate your support of the preservation process, and thank you for being an important part of keeping this knowledge alive and relevant.