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602 IMPROVEMENT OF

and thofe in the wooden cylinder, which are to correfpond with them, muft be nicely attended to.

Firft, when the tin-cylinder is foldered longitudinally, and one end of it foldered on, as at A, fix holes through it muft be made lonoi- tudinally on four oppofite fides of it, each hole muft be exaétly half an inch wide, and five eighths of an inch long, the length to be parallel to the length of the cylinder.

The centre of the firft of thefe holes muft be five inches diftant from the clofed end A, the centre of the fecond hole muft be eight inches diftant from the centre of the firft, and{o on till fix holes are made longitudinally along the cylinder, Then another{uch line of. fix fimilar holes is to be made on the oppofite fide of the cylinder, and then two other fuch lines between the former, in all twenty-four; and the fize of all thefe holes muft be nicely obferved, as well as their diftances.

Second}y. The wooden cylinder fixed on the axis is now to be in- troduced into the tin cylinder, but not quite to the end ofit, but fo as to leave exa@tly one inch of void fpace at the clofed end A, aud then the fize of all thefe apertures through the tin cylinder, each of which is exa@ly half an inch wide, and five eighths of an inch long, are to be nicely marked with a fine point on the wooden cylinder, which muft not previoufly have any excavations made in it.

Thirdly. The twenty-four holes thus marked on the wooden cy- linder are now to be excavated exa@tly three eighths of an inch deep, but with an addition alfo of three eighths of an inch at that end of every one of them which is next to À; fo that, when the wooden cylinder 1s again replaced in the tin cylinder as before, with one inch of void fpace at the clofed extremity of it, the excavations in the wooden cylinder will be three eights of an inch longer, than the per- forations in the tin cylinder over them. Thefe excavations in the wooden cylinder muft alfo be rather narrower at the bottom than at

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