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ed with smokeless powder is very sharp, and is as loud as when black powder is used, yet the volume of sound is much less, so that the report cannot be heard at so great a distance. The report of a gun using smokeless powder is a sound of much higher pitch than when black powder is used, and consequently cannot be heard at so great a distance as the lower notes given by black powder. As smokeless powder exerts a much greater pressure than common black powder when burned in a gun, one would naturally think that the recoil of the barrel would be greater, owing to the greater pressure exerted by the smokeless powder on the base of the cartridge case and the breech mechanism. However, such is not the fact; for the barrel actually recoils very much less when smokeless powder is used. This is due to the suddenness with which the pressure is exerted by smokeless powder, it acting more like a very sharp blow on the metal, whereby more of the energy is converted into heat instead of being spent in overcoming the inertia of the barrel to give recoil. Similarly when smokeless powder is fired in a gun, the displacement of the air is so sudden that the sound waves do not possess the same amplitude of recoil or vibration as is given by black powder. * * * * * THE CONSTRUCTION AND MAINTENANCE OF UNDERGROUND CIRCUITS. BY S.B. FOWLER. The numerous disastrous storms of the last winter have brought out very vividly the advantages of having all wires placed underground, and many inquiries have been addressed to the companies operating underground circuits as to their success. It is not probable that all of the answers to these inquiries have been of the most favorable character. To many central station managers an underground system means frequent break-downs and interruptions of service, with, perhaps, slow and expensive repairs, which bring in their turn numerous complaints, loss of customers, and reduced profits. In many installations burn-outs both underground and in the station are frequent, with the natural result that the operating of circuits underground is not there considered an unqualified success. The writer has in mind two very different experiences with underground cables. Several miles of cable were bought by a certain company, carefully laid, and up to to-day not a single burn-out or interruption of service can be attributed to failure of cables; at about the same time anot
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