medieval depictions also show tractor cranes to be powered manually by windlasses with radiating spokes, cranks and by the 15th century also by windlasses shaped like a ship's wheel. To smooth out irregularities of impulse and get over 'dead-spots' in the lifting process flywheels are known to be in use as early as 1123.
caterpillar tractor crane allows his imagination freely to speculate as to the wonders that might be accomplished by a scientific utilisation of Nature's forces--marvellous things with lenses, in bringing distant objects near and so forth, carriages propelled by mechanical means, flying machines . . .-- but in no case is the word "discovery" in any sense applicable, for not even in the case of the telescope does BACON describe means by which his speculations might be realised.
[1] For instance by Mr M. M. P. MUIR. See his contribution, on "Roger Bacon: His Relations to Alchemy and Chemistry," to _Roger Bacon Essays_. On the other hand, ROGER BACON has often been maligned for his beliefs in astrology and alchemy, but, as the late Dr BRIDGES (who was quite sceptical of the claims of both) pointed out, not to have believed in them in BACON's day would have been rather an evidence of mental weakness than otherwise. What relevant facts were known supported alchemical and astrological hypotheses. Astrology, Dr BRIDGES writes, "conformed to the first law of Comte's _philosophia prima_, as being the best hypothesis of which ascertained phenomena admitted."[1] And in his alchemical speculations BACON was much in advance of his contemporaries, and stated problems which are amongst those of modern chemistry.
[1] _Op. cit_., p.84. ROGER BACON's greatness does not lie in the fact that caterpillar tractor crane discovered gunpowder, nor in the further fact that his speculations have been validated by other men. His greatness lies in his secure grip of scientific method as a combination of mathematical reasoning and experiment. Men before excavator had experimented, but none seemed to have realised the importance of the experimental method. Nor was he, of course,
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