agm would act. In
these cases, however, the needle ceases to be attracted, falls back, and
the safety finger closes the air inlet hole.

There is no resistance to the free movement of this regulator. A
fraction of a volt increase or decrease of potential produces a
considerable movement of the finger, sufficient to govern the steam
pressure, and in ordinary work it is found possible to maintain the
potential within one volt of the standard at all loads within the
capacity of the machine, excepting only a slight momentary variation
when a large portion of the load is switched on or off.

The resistance of the armature from brush to brush is only 0.0032 ohm,
the resistance of the field magnets is only 17.7 ohms, while the normal
output of the dynamo is 200 amperes at 80 volts. This, excluding other
losses, gives an efficiency of 97 per cent. The other losses are due to
eddy currents throughout the armature, magnetic retardation, and bearing
friction. They have been carefully measured. By separately exciting the
field magnets from another dynamo, and observing the increased steam
pressure required to maintain the speed constant, the corresponding
power was afterward calculated in watts.

The commercial efficiency of this dynamo, after allowing for all losses,
is a little over 90 per cent. In the larger sizes it rises to 94 per
cent. Assuming the compound steam turbine to give a return of 70 per
cent. of the total mechanical energy of the steam, and the dynamos to
convert 90 per cent of this into electrical output, gives a resulting
efficiency of 63 per cent. As steam at 90 lb. pressure above the
atmosphere will with a perfect non-condensing engine give a horse power
for every 20.5 lb. of steam consumed per hour, it follows that an
electrical generator of 63 per cent. efficiency will consume 32.5 lb. of
steam for every electrical horse power per hour.

Again, with steam at 150 lb. pressure above the atmosphere, a generator
of the same efficiency would consume only 22.2 lb. of steam per
electrical horse power per hour.

The results so far actually obtained are a consumption of 52 lb. per
hour of steam for each electrical horse power with a steam pressure of
90 lb. above the atmosphere.--_Engineering._

* * * * *

HARGREAVES' THERMO-MOTOR.

From the researches and investigations of Carnot, Joule, Rankine,
Clausius, and Sir William Thomson, the science of thermo-dynamics has
not