[Illustration:  EFFICIENCY CURVES FOR THREE TYPES OF COMPRESSORS. (Fig. 8, 9, 10)]

Figs. 8, 9 and 10 are diagrams showing the comparative efficiency of the three types of compressors at St. Fargeau—­Fig. 10 being a diagram of the Riedler compressor—­and indicate the gain derived from the intermediate cooling.  The loss is shown to be only 12 per cent., as compared with a loss of 43 per cent. in a large part of the plant, and of 105 per cent. in the earlier compressors of the St. Gothard type.  The table given herewith contains a summary of trials made by Professor Gutermuth, and are intended to show the comparative results of an extended trial with three kinds of compressors at St. Fargeau.

PERFORMANCES OF COMPRESSORS AT THE ST. FARGEAU CENTRAL STATION.

--------------+-------+--------+------+-------+--------

+--------+---------+
| R   p |        |  E   |       |        |        |         |
| e o e | Horse- |  f   |Amount |Quantity| Cubic  |         |
Compressors.  | v f r | Power  |  f   |of Air | of Air |Feet of |Final Air|
| o     |Absorbed|  i   |Passing| Passing|Air per |Pressure.|
| l E m |   by   |  c   |through| through| Horse- |         |
| u n i |Compres-|  i   | Inlet | Valves | Power  |         |
| t g n | sors.  |  e   | Valves| per    | and per|         |
| i i u |        |  n   | each  | Hour.  |  Hour. |         |
| o n t |        |  c   |Revolu-|        |        |         |
| n e e |        |  y   | tion. |        |        |         |
| s   . |        |  .   |       |        |        |         |
--------------+-------+--------+------+-------+--------+----

----+---------+
|       |        |      | cubic |  cubic |        |lb. per  |
1.            |       |        |      | feet  |  feet  |        |sq. in.  |
Sturgeon    |       |        |      |       |        |        |         |
Compressor  |  37   |   302  | .87  | 41.67 |  91,507| 261.3  | 90      |
Diameter of   |  37   |   258  | .87  | 38.13 |  84,650| 276.1  | 90      |
cylinder,     |       |        |      |       |        |        |         |
23.62 in.     |       |        |      |       |        |        |         |
and 21.66 in.;|       |        |      |       |        |        |         |
stroke,       |       |        |      |       |        |        |         |
48.63 in.     |       |        |      |       |        |        |         |
|       |        |      |       |        |        |         |
2.            |       |        |      |       |        |        |         |
Cockerill   | 40    |   337  | .83  | 46.61 | 111,864| 281.83 | 90      |
Compressor. | 45    |   353  | .83  | 46.61 | 125,844| 302.66 | 90      |
Diameter of   | 40    |   342  | .88  | 49.43 | 118,632| 296.65 | 90      |
cylinder,     | 46    |   377  | .85  | 48.02 | 132,534| 298.77 | 90      |
25.98 in.;    | 38.67 |   324  | .89  | 50.14 | 116,434| 306.19 | 90      |
stroke,       | 38.5  |   337  | .89  | 50.14 | 115,818| 294.18 | 90      |