History of the Typewriter

— 94 — Before closing the account of this machine, it should be mentioned that the marginal arrangements consisted of a block threaded on an archimedian screw, which could be put out of commission by a touch, and in later models a similar device was used for the escapement. The accompanying illustration will show how this was used. It was an interesting experiment, and greatly improved the touch of the machine, since it took away the strain which otherwise existed between the dogs and the rack. Fig. 73 Group III.—Machines with Two Shift-Keys. The National. This machine, the invention of Mr. H. H. Unz, prints by means of twenty-seven keys and two shifts—eighty- one characters. The dimensions are 9x12 x 7I ins. high, with a weight of about 13 lbs. The keyboard is semi- circular in shape, and the keys, which are of black compo with white inlaid characters, are placed further apart than usual. It is considered that this leads to greater accuracy, inasmuch as it is almost impossible for the finger-tips to touch and depress two keys simultaneously. The carriage is very light, and will travel when raised, thereby assisting in the correction of errors. There is a guide on the carriage which enables envelopes, postcards, or small paper to be fed into the machine with perfect accuracy and freedom ; and the construction is such that folded papers may be passed into the machine and written upon with perfect ease and regularity.