Because Caligraph have space bars on the both side of keyboard each and placed there for other than thumbs, it's apparent, you see.
The revolutionary participation of thumb(s) might lead to touch.
It' s apparent? No, not for thumbs never. Then for which , finger or side of palm or so?
Some say for little fingers, some might say for side of palm.
It had been getting into the era typing sentences begun with capital letter then been continuing with smalls.
The No.2 Type-Writer has a very simple method of printing the capitals. In the left-hand coner of the key-board, at the bottom, is a key with "Upper Case" on it. To print the capital letters this key must be pressed down and kept there while the desired key or keys are struck. Beside being simple, this method has the advantage over those machines which have two sets of keys, of rapidity. On such machines the keys for the capitals are placed at each side, and the space-bar being still outside of them, much time is lost in carrying the hand over to the side to space between each word, and returning it. But on the Type-Writer the space-bar being in front the spacing is done with the thumb, and no time is lost, the fingers remaining over the key-board in position for striking the next letter. (page. 5, Introductory Explanations.)
Elizabeth Margaret Vater Longley Type-Writer Lessons for the Use of Teachers and Learners Adapted to Remington’s Perfected Type-Writers』(Cincinnati, 1882年)