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ENGINE MUFFLERS.
A great number of contrivances have been rigged up in England for the muffling of engines.  Bolton and Paul Company has gotten up a partitioned aluminum casting air-cooled exhaust manifold on the outlet extremity of which is fastened a light steel gauge exhaust manifold extension with a closed end.  This pipe is about three inches in diameter and about six feet long.  It is perforated throughout all its length on the outer half, away from the fuselage, with rectangular slots of about one inch by one eighth inch.  This apparently helps to dampen out the noises due to explosion enough to permit communication by word of mouth between pilot and observer.  The aluminum exhaust manifold is partitioned with telescopic joints extending between each pair of cylinders in the bank so as to do away with the possibility of cracking and reduce the strains due to cooling.  It is cooled by projecting aluminum fins so as to obviate the danger of fire which so often occurs from hot manifolds.

SUPERCHARGERS.

A DH-9 has been fitted with a supercharger which is very similar to our General Electric type.  Although results of their

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