he obtained the following values—
| Diameter of Pipe in feet. | α | β | ζ for 100 ft. per second. |
| 1.64 | .00129 | .00483 | .00484 |
| 1.07 | .00972 | .00640 | .00650 |
| .83 | .01525 | .00704 | .00719 |
| .338 | .03604 | .00941 | .00977 |
| .266 | .03790 | .00959 | .00997 |
| .164 | .04518 | .01167 | .01212 |
It is worth while to try if these numbers can be expressed in the form proposed by Darcy for water. For a velocity of 100 ft. per second, and without much error for higher velocities, these numbers agree fairly with the formula
ζ = 0.005 (1 + 3/10d),
(9)
which only differs from Darcy’s value for water in that the second term, which is always small except for very small pipes, is larger.
Some later experiments on a very large scale, by E. Stockalper at the St Gotthard Tunnel, agree better with the value
ζ = 0.0028 (1 + 3/10d).
These pipes were probably less rough than Arson’s.