SHOP TOOLS.

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enables the sizes of shop tools to be reduced, and their porta-bility and convenience thereby increased; but in case a lighterdescription of work bas to be done, the pressure ean be reducedby diminishing the weight in the accumulator.

The transmission of power by a pipe (instead of by belting orshafting) for actuating shop tools, is attended with advantages.Less wear and tear arises, and the power can be conveyed roundbends, or to distant points, with great facility. The pipes beingUnderground, the cost of the supports, columns, and bearingsrequisite for shafting is saved.

In the application of water-power to actuate machines thereis a great advantage in employing it at high pressure. Thepower (or foot pounds) transmitted through a high pressurewater main is determined by multiplying the number of poundsof water flowing per second by the pressure. If the same num-ber of pounds of water are delivered at 1500 Ibs. pressure to thesquare inch, double the energy is exerted as would be the casewith a pressure of 750 lbs. per square inch. If the same quantityof water is pumped through two pipes of the same diameter,the water in one being pumped at 750 lbs. per square inch, andin the other at 1500 lbs. per square inch, then every pound ofwater at 750 lbs. pressure contains 1700 foot pounds of energy,and every pound of water at 1500 lbs. per square inch contains3400 foot pounds of energy. In transmitting this volume of highpressure water, whatever number of foot pounds of energy werelost by friction in the water at the lower pressure, no morewould be lost by the water at the higher pressure, as friction isindependent of pressure. But as only half the high pressurewater will be required to do the work in comparison with thelower pressure water, the necessary velocity of the high pressurewater would be half that of the low pressure, and consequentlythe loss by friction would be less.

To Mr. Balph Hart Tweddell is mainly due the successfulsolution of the many practical difficulties which had to be over-come in applying hydraulic power to tools. In 1865 he deviseda small portable hydraulic apparatus for fixing the ends of boiler