could not be stopped. The tests two and four include all losses in the
service pipes, as well as the mains.

The production of compressed air at the central station is assumed at
30,000 cubic feet per hour (atmospheric pressure), and in all cases
the loss in the mains is taken as a percentage of the total
production.

The losses due to resistance in the mains were also examined with
great care, over independent sections, as well as through the complete
_réseau_. During the early part of these trials, an unusual and
excessive loss was recorded, the cause of which could not be at first
ascertained. At intervals along these mains are placed a number of
water reservoirs which receive the water injected into the mains; in
addition to these the direct flow of the air is interrupted by
numerous siphons, the stop valves to branches, etc. Investigation
showed that the presence of these reservoirs created considerable
resistance on account of an increased and subsequently reduced
section. The exact loss from this cause was, therefore, carefully
measured, as well as the losses existing in the mains not so
interrupted. The results show that the loss by expansion at one
reservoir, when the speed of the air flow was 23 ft. per second, was
equal to 0.15 atmosphere; with a speed of 29 ft. 6 in. per second, it
amounted to 0.2 atmosphere.

Therefore, the presence of five such reservoirs would cause a loss in
pressure equal to one atmosphere. This very undesirable arrangement is
not repeated in the new system, the sumphs being connected in such a
way as not to modify the section of the tube, nor consequently the
pressure of the air. The presence of the siphons and stop valves did