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 not seem to affect the pressure to any measurable extent. The following table contains a list of the more important mains tested, and it may be mentioned that the resistance, due to the reservoirs, was at first partially included. The trials were carried out while the mains were not being drawn upon by subscribers. ----------------------------------------------------------------------- | | Section of Mains Tested. | Length. |No. of | |Tests. | | ---------------------------------------------------+------------+------ | yards. | From the central station to the end of reseau and | | back to central station by return circuit | 18,100 | 7 From the central station to the Rue Fontaine au |\ 14,600 |/ 3 Roi |/ 9,900 |\ 4 From the central station to the Rue de la | | Charonne | 9,490 | 5 From the Rue de la Charonne to Fontaine au | | Roi | 4,770 | 3 From the central station to the Avenue de la | | Republique | 1,860 | 8 Various trials on different lengths of mains |770 to 8,000| 11 ----------------------------------------------------------------------- Over the whole system of 16.5 kilometers, which was also tested when no air was being taken off, there were four reservoirs of considerable size, and which offered a large resistance with a corresponding loss of pressure; on the line there were also 23 siphons and 42 stop valves. These trials were repeated several times to secure accuracy, and the speed of the air was brought to 49 ft. a second. The results obtained in one of these trials may be taken as an example. The main between the Rue St. Fargeau and the Fontaine au Roi, on which there are no collecting reservoirs, but three siphons and eight stop valves, gave, with an average speed of 21 ft. 3 in., a loss in pressure of 0.05 atmosphere for each kilometer of main.