With reference to these mains it may be mentioned that, unlike the 11.81 in. conductors of the St. Fargeau system, of which 17 kilometers are laid in the Paris subways, the new mains are entirely laid in the streets, it having been found impossible to make room for these large pipes in the subways already crowded with telegraph and telephone wires, water mains, etc.

Professor Riedler investigated the two causes of loss in the mains—­leakage and resistance.  It was superficially evident that the mains of the old system were so well laid, and the joints so well designed, that the loss from leakage was never a serious one.  In order, however, to ascertain the amount accurately, a series of careful experiments were carried out by Professor Gutermuth with the 11.81 in. mains of the St. Fargeau system.

  EXPERIMENTS ON LEAKAGE IN MAINS.

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--------------
| |                 |         |               |             | L P A |
| |                 |         | Air Pressure  |   Loss of   | o e i |
| |                 |         |  in Mains.    |  Pressure.  | s r r |
| |                 |         |---------------|-------------| s     |
| |                 |         |  B    |       |      |      |   C D |
| |System of Mains  | Length. |  e   T|       |      |      | o e e |
|N|    Tried.       |         |  g   r|  At   |      |      | f n l |
|u|                 |         |A i o i| End   |During| Per  |   t i |
|m|                 |         |t n f a|  of   |Trials|Hour. | A . v |
|b|                 |         |  n   l|Trials.|      |      | i   e |
|e|                 |         |  i   s|       |      |      | r o r |
|r|                 |         |  n   .|       |      |      |   f e |
| |                 |         |  g    |       |      |      |     d |
--+-----------------+---------+-------+-------+------+------

+-------|
| |                 | yards.  | atm.  |  atm. |      |      |       |
|1|Southern reseau  |         |       |       |      |      |       |
| | to Place de la  |         |       |       |      |      |       |
| | Concorde.       |  9,980  | 6.5   |  6.0  | 0.5  | 1.5  |  3    |
|2| Total reseau    | 18,500  | 6.9   |  5.9  | 1.0  | 1.5  |  6.3  |
|3|To Place de      |         |       |       |      |      |       |
| | la Concorde     |  9,980  | 7.0   |  6.43 | 0.57 | 0.75 |  2.16 |
|4|Total reseau     | 18,500  | 6.7   |  5.28 | 0.88 | 1.32 |  5.5  |
|5|Northern reseau  |         |       |       |      |      |       |
| | to Rue de Belle-|         |       |       |      |      |       |
| | ville.          |  1,530  | 6.0   |  5.0  | 1.0  | 0.6  |  2.3  |
|6|To the Rue des   |         |       |       |      |      |       |
| | Pyrenees.       |    600  | 6.1   |  3.7  | 2.4  | 0.56 |  2.2  |
------------------------------------------------------------

---------

These trials refer to the mains running from the St. Fargeau station to the Place de la Concorde, a length