TWO:Well may M. Havet say of the Academicians: ce sont eux et non les partisans dEpicure qui sont les libres penseurs de lantiquit ou qui lauraient voulu tre; mais ils ne le pouvaient pas.250 They could not, for their principles were as inconsistent with an absolute negation as with an absolute affirmation; while in practice their rule was, as we have said, conformity to the custom of the country; the consequence of which was that Sceptics and Epicureans were equally assiduous in their attendance at public worship. It is, therefore, with perfect dramatic appropriateness that Cicero puts the arguments of Carneades into the mouth of Cotta, the Pontifex Maximus; and, although himself an augur, takes the negative side in a discussion on divination with his brother Quintus. And our other great authority on the sceptical side, Sextus Empiricus, is not less emphatic than Cotta in protesting his devotion to the traditional religion of the land.251A gravity wheel must have a diameter equal to the fall of water, or, to use the technical name, the height of the head. The speed at the periphery of the wheel cannot well exceed sixteen feet per second without losing a part of the effect by the wheel anticipating or overrunning the water. This, from the large diameter of the wheels, produces a very slow axial speed, and a train of multiplying gearing becomes necessary in order to reach the speed required in most operations where power is applied. This train of gearing, besides being liable to wear [38]and accident, and costing usually a large amount as an investment, consumes a considerable part of the power by frictional resistance, especially when such gearing consists of tooth wheels. Gravity wheels, from their large size and their necessarily exposed situation, are subject to be frozen up in cold climates; and as the parts are liable to be first wet and then dry, or warm and cold by exposure to the air and the water alternately, the tendency to corrosion if constructed of iron, or to decay if of wood, is much greater than in submerged wheels. Gravity wheels, to realise the highest measure of effect from the water, require a diameter so great that they must drag in the water at the bottom or delivering side, and are for this reason especially affected by back-water, to which all wheels are more or less liable from the reflux of tides or by freshets. These disadvantages are among the most notable pertaining to gravity wheels, and have, with other reasonssuch as the inconvenience of construction, greater cost, and so ondriven such wheels out of use by the force of circumstances, rather than by actual tests or theoretical deductions.
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