Martin Howard from Antique Typewriter (previously) writes, "In 1881, Thomas Hall, a Brooklyn engineer, invented the first portable typewriter that would enable a person to type with the machine anywhere, even on one's lap. This was also the first index typewriter, a typewriter with no keyboard that requires one to use a selector. In this case, a black handle is depressed to choose the characters when typing. The Hall, despite its unusual design, proved to be quite successful over the next twenty years."
Howard recently redesigned his site, which is a showcase for his impressive collection of 19th century typewriters.
The Hall originally sold for $40, an economical alternative to the $100 keyboard machines; a good horse-drawn carriage could be bought for $70. At a time when few people knew how to type efficiently with both hands, it would have seemed reasonable to the operator of the Hall to pick out the characters using one hand.
To type, the black handle is moved around over the holes (each hole is a different character) to select the characters. Then a stylus, on the underside of the handle, is pushed down into one of the holes to print that character. Inside the typewriter, a rubber plate that has all the characters moulded on its surface, has moved into position allowing for the correct character to be pushed onto the paper.
The rubber type could be quickly changed for different fonts and languages.
Hall 1 Typewriter