Another recently appearing machine is the “Oliver.” This has type bars which are normally above the work. Each bar is loop shaped, hinged at its lower ends, and bearing the type letter on the bend at the upper end. They are arranged in two series, one on each side of the center, and in printing each loop swings down like the wing of a bird. As the printing is from the top, and the ribbon is moved away from in front of the line immediately after the printing blow, the writing is always visible to the operator. This machine is manufactured under various patents to Thomas Oliver, the first of which was No. 450,107, granted April 7, 1891. Further improvements are covered by subsequent patents, Nos. 528,484, 542,275, 562,337, and 599,863. The Oliver has made many friends for itself by its fine alignment and visible writing, and shares with the other standard machines a considerable patronage. It is not practicable to give a full illustration of the state of the art in typewriters, as it has grown to an industry of large proportions. Nearly 1,700 patents have been granted for such machines, and more than 100 useful and meritorious machines have been devised and put upon the market. Among these may be mentioned the Hall, Underwood, Manhattan, Williams, Jewett, and many others. [Illustration: FIG. 143.--ELLIOTT & HATCH BOOK TYPEWRITER.] Besides the regular typewriters, various modifications have been made to suit special kinds of work. The “Comptometer” used in banks is a species of typewriter, as is also the Dudley adding and subtracting machine, known as the “Numerograph,” and covered by patents Nos. 554,993, 555,038, 555,039, 579,047 and 579,048. Typewriters for short hand characters, and for foreign languages, and for printing on record and blank books, are also among the modern developments of this art. In the latter the whole carriage and system of type levers move over the book. The Elliott & Hatch book typewriter, Fig. 143, is a well-known example. In attachments, holders for the copy have received considerable attention, and simple and practical billing and tabulating attachments have been devised which expedite and facilitate the statements of accounts and other work requiring numeration in columns. The Gorin Tabulator is one of those in practical use.