...To speculate was to wound himself in vain... 
Rafael Sabatini 「Captain Blood」
...It was useless to speculate upon chances...
Samuel White Baker 「In the Heart of Africa」
...He tried to speculate on my Christian character...
Henry Bibb 「Narrative of the Life and Adventures of Henry Bibb, an American Slave, Written by Himself」
...He did not speculate concerning the origin of these injuries...
Henry S. Fitch 「Field Study of Kansas Ant-Eating Frog」
...'Well, then, will you speculate on him yourself for the buss-masters?'asked Mr...
R. S. Surtees 「Mr. Sponge's Sporting Tour」
...He then went on to speculate as to the cause of the planets' motion...
Oliver Lodge 「Pioneers of Science」
...Every work on astronomy tells in a general way of thebelts of Jupiter, and many speculate upon their causes...
Simon Newcomb 「Side-lights on Astronomy and Kindred Fields of Popular Science」
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