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 of the water, and even the nature of the micrometer divisions, so as to observe the different displacements without being able to presuppose the value. In fact, the greatest influence to be feared was that of preoccupation while measuring small quantities which involved a great deal of estimation. I believe that the results I have obtained have been free of this cause of error.

The greater portion of the observations were made at a speed of 7.059 meters per second. A certain number of them were made at a speed of 5.515 meters per second, and some were made at 3.7 meters per second. The observed values were reduced to the maximum speed of 7.059 meters per second, and related to the length of a fringe taken as unity.

By doubling the average value, 0.46 is obtained, which is very close to half a fringe, and which represents the displacement value produced when the flow in the tubes is reversed.