Robinson--Pola~-ization of Sound.
201
The one hundred and eighty pieces were of cast iron, were exactly :alike and interchangeable.
Great care was taken in fitting them to keep the metal cool, as it was ibund that holding one of the pieces, which had been fitted to gauge, in the hand for a few seconds would expand the metal so that it would not reach the bottom of gauge by a sixteenth of an inch; ~]so, that inserting a piece of tissue paper, equal in thickness to the thousandth part of an inch, in the side of gauge would have the same effect. When the pieces were first fitted to ~he wheel it was found that they lacked three-sixteenth inch of a perfect circle, which made it necessary to reduce very Slightly the diameter of the.wheel. This was done by revolving the wheel very slowly by hand on a vertical fixed axis, which acettrately fitted the hole in wheel, against a stationary cutter, very hard and very sharp, making necessarily more of a serape than a cut. Then the pieces were again fitted, and it was found all had to be altered, owing to the change in the size of wheel. This operation was repeated many times, and although much time was spent it was deemed advisable in attaining the perfection desired.