FORE:A pressure wheel, like a steam-engine, must include running contact between water-tight surfaces, and like a rotary steam-engine, this contact is between surfaces which move at different rates of speed in the same joint, so that the wear is unequal, and increases as the speed or the distance from the axis. When it is considered that the most careful workmanship has never produced rotary engines that would surmount these difficulties in working steam, it can hardly be expected they can be overcome in using water, which is not only liable to be filled with grit and sediment, but lacks the peculiar lubricating properties [41] of steam. A rotary steam-engine is in effect the same as a pressure water-wheel, and the apprentice in studying one will fully understand the principles of the other.Philosophy was no sooner domiciled at Athens than its professors came in for their full share of the scurrilous personalities which seem to have formed the staple of conversation in that enlightened capital. Aristotle, himself a trenchant and sometimes a bitterly scornful controversialist, did not escape; and some of the censures passed on him were, rightly or wrongly, attributed to Plato. The Stagirite, who had been brought up at or near the Macedonian Court, and had inherited considerable means, was, if report speaks truly, somewhat foppish in his dress, and luxurious, if not dissipated in his habits. It would not be surprising if one who was left his own master at so early an age had at first exceeded the limits of that moderation which he afterwards inculcated as the golden rule of morals; but the charge of extravagance was such a stock accusation at Athens, where the continued influence of country life seems to have bred a prejudice in favour283 of parsimony, that it may be taken almost as an exoneration from graver imputations; and, perhaps, an admonition from Plato, if any was needed, sufficed to check his disciples ambition for figuring as a man of fashion.
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