ピリオドのあとにスペース２つ開けてから次の文頭文字を打つ書法は 大文字タイプライターの時代の決め事として誕生したのかな？

いつごろから　大文字小文字混じりタイプ文が　標準とされるようになったのだろうか、

それまでは とりあえず 大文字タイプ文書のほうで 一旦 法廷内部でのタイプ書式が 定まっていた？

For a time the bench and bar were content with the all capital writing, as it was a great step in advance of the pen writing previously in use, but, united with the desire for something better, the reading of this style of print has become too monotonous to the eye to be borne, and the general sentiment is now in favor of the upper and lowercase writing, or caps and small letters. The difficulty with the all capital writing was obviated to some extent by double spacing the lines, but the additional trouble this involved is avoided by the use of capitals and small letters, printed with which the record is no doubt read with less fatigue to the eye than the double spacing with all capitals.

A. J. Henderson.Toronto, Ont., How to prepare a court record., Paper read at the International Congress of Shorthand Writers, Toronto, August l6thand 17th, 1883:, Brown & Holland shorthand news. Vol. II., Nov. 1883. No. 11., p. 227.
Brown & Holland shorthand news. v. 2 (1883). - Full View | HathiTrust Digital Library:

大文字 小文字 混じり文でのタイピング、
大文字だけ機でのタイプと比べて タイムロスは　10パーセント以内だとかも。